Designing with Dog Friendly Plants – Expanded

Note: This article is an elaboration of a quick post we did last year about creating dog friendly landscapes. The topic has only gotten more popular, so we have written a new post with much more information and many more resources!

Dog Friendly Landscapes

Dogs: they’re everywhere! Whether you work in the city or the suburbs, chances are you have had clients with dogs. According to a 2017 survey, 60% of households in the US own a dog, so the desire to create “dog friendly” landscapes is widespread.

But what is a dog friendly landscape?

A dog friendly landscape really means two things:

  • A landscape where dogs can be safe from toxic or harmful plants
  • A landscape that resists the negative effects dogs can have on plants

Dog-Safe Landscape

Choosing non-toxic plants is the easiest part of designing a dog-friendly landscape. The Plantium has a quick toxicity filter to eliminate from your search plants that might harm your client’s cat or dog.

If you are not using The Plantium, do a quick check of your plant list against any one of the toxicity lists widely available on the internet. The ASPCA, for example, has compiled a great list of plants to avoid when considering a yard with a pet.

Dog-Resistant Landscape

This is a much trickier proposition, and probably the reason most of you are reading this article.

Between digging, trampling, and plant-killing urine man’s best friend is far from the best friend of your landscape design. This problem is particularly exacerbated urban situations, where many dogs are concentrated in a small area

But taking fido’s impact on the landscape into consideration from the very beginning of the design will lead to a better long-term product and happier clients in the end.

Design Layout

Although each breed behaves differently, some dog traits are universal: patrolling, bedding down in cool shady areas, and urinating. Designate spaces for all these things in your design, and create barriers with edger, fencing, or very dense plants, to discourage dogs from being in areas where they don’t belong. Check out this article in Sunset Magazine for an example of a dog-friendly garden and dog friendly design layout tips.

Dog damage to fescue lawn.

Dog damage to fescue lawn.

Plant Selection

Dogs are hard on plants! Specifically, dog urine is hard on plants. To understand how we can combat this, we need to first understand what is wrong with the whiz. According to an article published by The Turf Resource Center the nitrogen in dog urine is to blame.

Dog urine is basically liquid fertilizer, and in small doses can actually make plants happier! The problem is that it is usually delivered in large concentrated doses, particularly by female dogs. Male dogs can also overload plants through repeated marking, or marking by multiple dogs.

Just like with any fertilizer, an overload of dog urine will cause “burning.” This is caused by the nitrogen salts in the fertilizer (or urine) drawing water out of the plants. In perennials and shrubs this manifests as yellowing or crunchy brown leaves, and in turf it manifests as a large dead patch.

Fertilizer burn on lawn and shrub.

Including a designated “bathroom” area in your design is one way to minimize the damage doggie damage. But if you know there will be many dogs moving through, such as in a condo or apartment landscape, you should also consider dog urine resistant plants.

Certain species of turf handle dog urine much better than others. Fescues and perennial rye grass handle dog urine much better than Kentucky Bluegrass and Bermuda Grass. In fact there is even a new turfgrass cultivar called Dog Tuff (Cynodon ‘PWIN04S’) bred specifically to resist dog urine!

When choosing perennials, shrubs and trees at risk of heavy exposure to urine, look specifically for plants that can withstand saline soils and/or salt spray. With appropriate irrigation, these plants are much less likely to show the “burn” effect associated with large amounts of dog urine.

Use The Plantium to filter for both of these criteria to quickly find great dog resistant plants!

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Plant of the Month: Lonicera korolkowii ‘Floribunda’

Lonicera korolkowii ‘Floribunda’

BLUE VELVET honeysuckle

When you can combine pollinator attraction and ungulate resistance, this Plant Select® shrub is always a winner. The Blue Velvet honeysuckle gets even better than that, though!

It’s umbrella arching form spreads beautifully in the garden and creates a lovely background filler and focal point that engages throughout the season. In early spring the pinkish, purplish flowers are plentiful and very fragrant. These give way to blue-green foliage in summer and starting in late summer the red berries develop and can become quite plentiful. Bees, butterflies and birds are all attracted to this gem in the garden. There is no fall color to speak of, but the lovely form of the shrub itself makes up for that.

The original blue leaf honeysuckle is native to the central Asia, Pakistan and Afghanistan mountains which means it adapts well to high arid conditions in the western US. It is very pest resistant and extremely drought tolerant once established making it one of just a handful of mid-sized trees that stand out so buoyantly in the xeric garden.

Blue Velvet prefers full sun to part shade, with a wide range of pH soil, and a wide USDA zone (3-8). It mature height is 12’ and is a moderate grower so you’ll see it fill out in the garden in fairly short order. It’s going to get at least as wide as it is tall and has an irregular, arching form to its branching.

While not listed as noxious in any states, it is important to note that this honeysuckle can escape the garden readily after birds eat and drop the seeds. It should be used with caution, especially in the Northeastern US.

Soil Depth and Plant Selection

Dive into The Shallow End

As designers and installers we are tasked with creating landscapes in all sorts of conditions. Often these conditions are challenging and not necessarily what plants might prefer in their natural environments. Soil depth is one of the most common challenges we face. From containerized plantings on a pool deck, to street trees or green roofs, almost every designer will eventually need to choose plants for a constrained location.  This article will give you some insight into creating successful plant designs in tight places!

The definition of limited soil volume!

Talk about limited soil depth!

Making sure your plants have enough room to root seems like it would be the primary concern when creating a design with restricted root space. However there are really multiple factors you have to consider before you even get to soil depth!

Proper Drainage

Planting areas with restricted soil depth or restricted soil volume are notoriously prone to drying out quickly, but don’t be fooled into thinking you don’t need to address drainage! Whether your planting bed is in the lawn, green roof or a planter, proper drainage is crucial. While certain plants can survive inundation in a natural setting, standing water or improper drainage will quickly de-oxygenate and compact the soil in contained situations and kill your oh-so-carefully selected plants. There are many ways to tackle drainage and all are dependent on the design situation. If you are working on a new install, drainage is first and most important thing to get right, as is can be difficult and costly to fix down the road. If you are working in an area with existing poor drainage, find solutions before considering any next steps!


Soil Health and Longevity of the Design

The anticipated lifespan of landscapes varies considerably. Before you choose plants, consider how long you anticipate your design persisting before a “refresh.” Are you creating a container design that will be replaced every year or even every season? Are you planting trees and shrubs you want to see mature over time?

Planting areas with restricted root space require monitoring of soil health. The more restricted the soil volume, the more quickly that soil will be depleted of nutrients crucial to the plant’s health. However if a refresh of the plant material (and soil) is planned to occur frequently, then shallower soil profiles can be no problem. If the design contemplates trees and shrubs that are intended to grow to maturity over time, then a more significant soil volume should be considered to promote long-term plant health.

Proper Plant Selection

Let’s look at those tough little plants growing in the cracks and crevasses! Plants that grow in these conditions in the natural world tend to be tough, resilient, vigorous, and drought tolerant plants. If you have all the right soil and bed conditions but choose sensitive plants, it is likely your design will still struggle without intensive care. And don’t forget how soil volume can affect plant hardiness. Plants with reduced soil volumes, especially container plantings, are much more susceptible to larger swings in soil temperature. If you are planting long-lived plants in containers it is best to pick plants at least two zones hardier than you normally would.

Don’t forget, The Plantium can help you quickly select plants for even the toughest planting project!

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Soil Depth

And now we finally come to soil depth.

We have all seen the beautiful and resilient plant that appears to be growing happily, in what appears to be almost no soil volume. However, plants grown in-situ from seed are are much more successful establishing themselves in challenging growing areas than transplants.  Imagine going from a pot in a comfortable nursery to being blasted by sun and heat in a roof deck! To have you transplanted plants thrive, follow these basic rules of thumb for soil depth.

Plant Type Plant Height Minimum Soil Depth
Annuals Any 3”
Turf Grass NA 4” (3” in warm climates)
Perennials <8” 4” (3” in warm climates)
Perennials 8”-16” 6”-8”
Perennials/ Ornamental Grasses/ Shrubs 16”-24” 12”-18”
Perennials/ Ornamental Grasses/ Shrubs 2’-6’ 24”
Shrubs/ Small Trees >6’ 3’ Minimum (should consider overall volume as well)
Trees All Should be calculated on overall volume for each tree and not just soil depth

If you are looking for more information on soil depth and bed construction, check out this great article by Proven Winners.


Lastly, on-going maintenance is the greatest issue facing these planting designs. In addition to soil replenishing mentioned above, containerized plants can also suffer from large swings in soil moisture. Because they are prone to drying, too much irrigation is often applied, and over-watering is perhaps the most frequent maintenance faux pas committed against plants with restricted root space. Carefully working with the maintenance team is critical to head off this issue early on.

Happy Planting !

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Importance of the Allergy Friendly Landscape

Most of us think summer sneezing just ‘comes with the territory’ but did you know that you can alleviate some of it with an allergy friendly landscape!  As landscape professionals, the concept of an allergy friendly landscape is a crucial one. Regardless of the scale of a project our understanding of high pollen generating plants is critical to making some changes for the better in our cultivated landscapes.

Wind blown pollen

Wind blown pine tree pollen. Makes me sneeze just looking at it!


Most of us suffer from just a little sneezing and sniffling from seasonal allergies but the implications of high pollen rates can be far more serious. “Deaths from asthma continue to climb each year at alarming epidemic rates”.1 While the causes of these increases can be debated it is clear that high pollen rates play a role in many health related issues, especially in the young, old and those with compromised respiratory and circulatory systems.

Studies have shown death rates among high-risk populations increase on days with high pollen and high pollution. Similar to the association of very hot or very cold weather to higher death rates, one cannot attribute it directly to the weather condition but rather see a correlation in high-risk populations.2 Impacts like thunder death outbreaks also bring home shocking impacts of high pollen in urban settings.3

So, how did we arrive at the increases in allergies and asthma? We all know the issue relates to high pollen counts, but what is pollen and has atmospheric pollen been on the rise in recent years? Pollen is the microscopic grain carrying the male gamete of a plant that will pollinate (via transport by insects, birds, wind, etc.) the female ovule of a plant. This microscopic grain is both an irritant and a nasal allergen in humans (and other animals; yup, dogs get allergies). Anemophilous plants generally cause the most allergies because they pollinate primarily by wind. The pollen grains of those plants are light and small, in order to be easily dispersed by the wind (and therefore tend to stay airborne and easily breathed in by humans). The role of female plants in an allergy friendly landscape is critical because they are attractive (for sure 🙂 )! The pistil of female plants is STICKY in order to capture the pollen grain. In an allergy friendly landscape female plants (and flowers) are important because they both do NOT produce pollen, AND they pull pollen out of the air with sticky attractiveness! Two other important aspects of pollen creation are important to understand as well – pollen production is increased dramatically with additional CO2 in the atmosphere (urban settings) and changes to the timing of pollen generation is being sparked by increased climatic temperatures.

Microscopic Helianthus Pollen

Microscopic Helianthus Pollen – it sure looks like it would irritate anybody’s nose!

So what does this have to do with the cultivated landscape and an allergy friendly landscape? This is where the concept of botanical sexism comes into our vocabulary. “Arborists often claim that all-male plants are ‘litter-free’ because they shed no messy seeds, fruits or pods. In the 1949 USDA Yearbook of Agriculture, which focused on trees and forests, this advice was given to readers: ‘When used for street plantings, only male trees should be selected, to avoid the nuisance from the seed.’ In the years following, the USDA produced and released into the market almost 100 new red maple and hybrid-maple-named clones (cultivars), and every single one of them was male.”4 At The Plantium, we believe male cultivars have an important place in the landscape, but it is important to understand that the use of male (and only male) cultivars and overall plant selection play the most important role in developing an allergy friendly landscape.

Scope and Scale

When and where it is important to think about an allergy friendly landscape? There are many projects where understanding the right plants for a low allergy and allergy friendly landscape are important. Being conscious of pollen generation on all your projects can help address the growing issue of high pollen in the cultivated landscape. Our responsibility as landscape professionals should be taken seriously! Consider your client when embarking on a residential design. Just asking the question about any allergy or asthma sufferers in the household (and then designing an allergy friendly landscape) can help make a successful landscape and a happy client. Allergy friendly landscape plant selection is most important around high risk populations, including playgrounds and senior living projects. Finally, projects in urban centers should be addressed carefully as the greatest population of allergy and asthma sufferers per capita reside in cities.

Amaryllis Stamen

Up close and personal on the Amaryllis stamen. The sticky pistil of an amaryllis flower gathers up all this pollen for fertilization!

Making Great Plant Choices

All of this background begs the question… what do we do now? Here are a few thoughts.

  1. Understand and educate yourself on the benefits of the allergy friendly landscape.
  2. Familiarize yourself with the OPALS rating system. Thomas Ogren created the first and only known rating system that ranks the allergy potential of plants.
  3. Discuss the need for an allergy friendly landscape with your client.
  4. Educate yourself on types of plants that might fit in an allergy friendly landscape and follow a few best practices such as:
  • Gender balance the landscape.
  • Use fewer wind pollinated species.
  • Encourage sterile cultivars and showy flowers (most plants with big colorful flowers are insect pollinated! Bees welcome?!).
  • Avoid high pollinators: male only willows, poplars, aspens, ash, (fruitless) mulberry, cypress, junipers, yews, myrtles, currants, etc., olive trees, Bermuda grass. Fruit trees are good but nut trees tend to be allergenic.
  • Develop maintenance manuals for your clients that encourages trimming of existing high pollinators and good maintenance of installed plants (e.g. trimming privet before it flowers). The Healthy Schoolyards Initiative5 has a great start at a list of maintenance measures that can be undertaken on existing landscapes.

The Politics of Allergy Friendly Landscapes

While it appears uncertain that low pollen ordinances are having an impact, landscape professionals should be aware that there are a growing number of urban centers enacting pollen control ordinances, including Pima County, AZ, Clark County, NV, Albuquerque, NM, Phoenix and Tucson, AZ, and El Paso, TX, among others. Other cities such as Louisville are embarking on some truly innovative approaches to understanding and addressing the epidemic.


While we can thank pollen for so many wonderful things like solving murders (it’s a plant’s fingerprint!), determining the age and quality of coal seams, and our delicious fruits and vegetables we now need to be stewards of our own air and address the issue of excessive pollen in our cultivated landscapes!


  1. Copyright 2001, Tom Ogren

Image References

The Importance of Tree Root Structure

Whether you’re dealing with a pansy or a ponderosa, everyone understands that healthy roots are crucial for a healthy plant. But nowhere is a healthy root system more important than in trees, the highest value and most long-lived asset in any landscape. Making good species choices for above ground AND below ground conditions is the first step in designing a landscape that will thrive into maturity.

We have all seen the potential damage done by tree roots as they crack sidewalks, clog sewer lines, and penetrate foundation walls. An unfortunate consequence of this destruction is that mature trees are often removed to salvage the surrounding hardscape or infrastructure. This can be avoided with a better understanding of structure and behavior of tree roots.

One Size Doesn’t Fit All

One of the first misconceptions is that each particular species of trees will have a predictable root structure. While this may be generally true in ideal growing conditions, huge variations occur based on underground obstacles, soil quality, and localized availability of nutrients, oxygen and water.

‘Root growth is essentially opportunistic in its timing and its orientation. It takes place whenever and wherever the environment provides the water, oxygen, minerals, support, and warmth necessary for growth.’1

If compacted soil exists below the ground then the tree will typically continue lateral root growth above that layer of compaction. This is very typical in urban situations where compaction and poor drainage is a common issue. Trees will root to similarly shallow depths if placed above rocky shelves or perched/high water tables. However, the roots of  same species may grow to great depths in sandy soils.

Our Roots Don’t Run THAT Deep

A second misconception is related to the overall size and depth of the root structure for a healthy tree. Tree protection requirements in most jurisdictions require only protection of the tree root structure to the dripline but a healthy root system may extend significantly larger than that!

‘The major roots and their primary branches are woody and perennial, usually with annual growth rings, and constitute the framework of a tree’s root system. The general direction of the framework system of roots is radial and horizontal. In typical clay-loam soils, these roots are usually located less than 20 to 30 centimeters (8 to 12 in) below the surface and grow outward far beyond the branch tips of the tree. This system of framework roots, often called “transport” roots, frequently extends to encompass a roughly circular area four to seven times the area delineated by an imaginary downward projection of the branch tips (the so-called drip line).’1

The size of the root infrastructure is affected by the tree species, but more significantly impacted by soil conditions and access to resources. If a tree species that would normally grow a tap root but runs into heavily compacted soil, it will simply continue the lateral growth out instead of down. When designing for trees in any conditions, think about your ‘container’ below ground. Where are the barriers at and below the surface, and what might the roots do once they encounter those barriers?

Rascally Roots

Certain species of trees are traditionally considered a ‘no-go’ when designing in constrained spaces such as urban areas, small backyards, and near sidewalks and utilities. These species are off limits for different reasons. For example ficus, some poplars, and silver maples, have aggressive flat (meaning lateral and shallow) primary root structures. Trees of this type are known for creating knobs in lawns and heaving adjacent paved surfaces. Other trees such as willows, American elms, and robinia are generally off limits because of their love of water and their extremely extensive root systems. Trees of this type are often responsible for invading leaky water or sewer pipes, or sending up problematic shoots a great distance from the mother tree.


Problematic roots.

Stop Problems Before they Start

Solving for problem roots is difficult and frequently results in significant damage to mature trees. It is better to avoid problem roots altogether. The best way to do this, no matter the tree type, is to prepare and maintain a fantastic habitat for the root system so it doesn’t need to travel far to provide everything the tree needs.  If possible, minimize compaction and provide sufficient water and nutrients within an area approximately 2 – 4 times larger than the tree’s dripline. And remember, anything you apply to the ground in this area, including herbicides. can have an immediate impact on the tree. If you are planting small trees take into account the mature width of the tree when planning for its root system. Try to keep tree trunks at least 4′ off of pavements or obstacles to allow for root spread.

When this is not possible (for example if you are working in urban or constrained areas) structural soil, Silva Cells, etc. are all great tools in constructing the correct ‘container’ for the tree’s root structure. These types of systems prevent compaction which can encourage roots to grow at the surface causing heaved pavements, etc. Even if these elements are not required in urban settings where you work, consider doing some research and incorporating them anyway. This can take the longevity of an urban street tree from 5-8 years to 30+ years!

If there is an area you do not wish tree roots to invade, consider including a vertical root barrier. But be aware that if a tree’s root develop too lopsided the tree is more prone to blowing over. Lastly, make sure the root zone is protected with an appropriate depth of mulch or vegetative cover to maintain soil temperature and prevent drying. With a few simple precautions your trees AND the surrounding hardscape can all enjoy a long happy life!


  1. Thomas O. Perry


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Win at Planting Design with Criteria-Based Plant Selection

We’ve all been there: You have poured effort into creating a strong design concept that is carried through your forms, your hardscape, and even your site furnishings. Your project is shaping up to be a wonder of landscape architecture. Then you get to 50% CDs and 100% budget, and now it’s time to do the planting design…

It can all fall apart when it comes to planting.

Plants make a very powerful contribution to the aesthetic of a project. But selecting plants can be an arduous process that you don’t always have the time or budget for. In my landscape architecture firm we used to often find ourselves recycling plant lists from previous projects to save time. However each project has its own style, and try though you might you are not going to achieve new and unique aesthetics by using the same old plant list!

The most effective way to make sure every planting design is unique AND successful is to use a combination of criteria-based plant selection – selecting plants based on specific desirable traits that support the aesthetic and environmental goals of the project – and modern tools such as Pinterest and The Plantium.

Try The Plantium to quickly find great new plant selections for every project, or read on to learn 4 quick steps to compile your criteria and OWN your next planting design project.

Expand Your Plant Palette

Step 1: Growing Conditions

Each plant requires specific conditions to thrive, so you must understand your growing conditions before you start choosing plants. Often your design will be subdivided into discrete planting areas with different environmental conditions. Start by documenting at least the most basic environmental conditions for each area:

  1. Hardiness zone
  2. Exposure
  3. Water use

Some projects may also require more in-depth consideration of factors such as reflected heat, extensive heavy clay, highly saline soils, potential foot traffic, etc.

And don’t forget: it is the height of embarrassing to specify invasive plants, so make sure to avoid plants categorized as noxious or invasive in your project area!


Step 2: Aesthetics

Now it’s time for the fun part!

Before you select even one plant, refresh yourself on your project’s design concept. Harken back to the fundamentals of your design and consider how the planting should work to promote the concept, style, forms and focal points you have created.

Plant Selections Varies Greatly with Design Style

Is your design rustic? Tropical? Modern? No matter where your project is located, the texture, scale, density, and variety of plants you select can make all the difference in achieving your design aesthetic. Ask design questions such as: What should the scale of the plants be in relationship to people and other elements such as the architecture? How dense should the planting be to achieve your style? How complex should the palette be?

Make simple statements in answer to your design questions, and use these to then flesh out your criteria in increasing detail.

Looking at example imagery can be highly useful in this phase!

Example of plant imagery board.

Let Pinterest be your guide, and make note in each image of how the aesthetic is achieved using plants as design elements.

Now focus on your individual planting areas. Use sketches in perspective view and bubble diagrams in plan view to create the bones of a planting design that reflect your design statements. Create your design as if you were blocking out a painting; thinking not about specific plants, but about what elements would make the most beautiful composition. 3D models are extremely helpful in this process, if your perspective-sketching skills are as tragic as mine!


Sketches to determine aesthetic criteria.

Your sketches don’t have to be pretty or time consuming! But they are an invaluable way to visualize your planting design in concept before choosing plants.

Step 3: Pick Some Plants – Finally

By this point you have created a (possibly extensive) list of environmental and aesthetic criteria that you can use as a guide when selecting plants. If you like plant selection the old-fashioned way, you can download our spreadsheet template to help document your criteria/plants, and build a plant list from your library of books, catalogs, and websites.

Example Plant Criteria Spreadsheet

But wait! Fortunately designers are increasingly able to put aside the manually created spreadsheet and pile of books for a more efficient process! Planting designers can now turn to the ever-useful internet and tools such as The Plantium that feature faceted searching and list building capabilities to make quick work of compiling your plant list using all the criteria you identified.


Planitum Search Page

Online programs like The Plantium make searching for plants using your criteria a cinch, and even let you create and evaluate plant lists automatically.


Step 4: OWN that Planting Design

No more “shrubbing it up,” and no more feeling less than confident about a design that is being presented to a client or (even worse!) about to be put in the ground. Use the tips above to make every planting design a great one, starting with great plant selection!


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Understanding Nursery Stock Sizes

It’s time to build your plant lists…. And there’s one thing to remember. Size matters! But understanding and deciphering standard nursery stock sizes can be like trying to find your way out of an Iowa cornfield. You’re bound to get lost a few times. Everyone calls out nursery stock sizes differently. Gallons, flat size, tree height, or caliper have all appeared in our plant lists. But depending on your familiarity with the nursery industry, you may not know that there is a continuously updated national standard on how to spec nursery stock sizes!

When writing this blog, I set out to include a nice handy, dandy all-purpose cheat sheet for our landscape professionals but it turns out that is easier said than done! Instead, this article provides a brief overview of the standard and can get you started on the right path to learning more for the next time you specify plants. We cannot promise that your suppliers will be following this standard to the number and letter, but if you stay familiar with the standards you will be much more likely to specify the nursery stock sizes that are available.

Specifying the Right Sizes Takes Knowledge

Specifying the Right Sizes Takes Knowledge

Called the American Standard for Nursery Stock, this national standard is published and maintained by AmericanHort, which is a somewhat recently formed consolidation of the American Nursery & Landscape Association and OFA—The Association of Horticultural Professionals.

According to AmericanHort, “The purpose of the American Standard for Nursery Stock … is to provide buyers and sellers of nursery stock with a common terminology, a ‘single language,’ in order to facilitate commercial transactions involving nursery stock. For instance, the Standard establishes common techniques for (a) measuring plants, (b) specifying and stating the size of plants, (c) determining the proper relationship between height and caliper, or height and width, and (d) determining whether a root ball or container is large enough for a particular size plant.”

The organization has been publishing this nursery standard since 1923, and it was adopted as a national standard in 1949 (ANSI Z60.1-2014). The most recent revision to the standard was published in 2014, and is available free from AmericanHort HERE. Use of this standard when growing and specifying plants is voluntary, but it is widely accepted and often referenced in standard specification sections. Using the standard has many benefits for designers and contractors, not the least of which is simplifying the procurement and acceptance processes by relying on clear pre-defined standards for quality and size of nursery stock.

The complete standard may be a daunting 109 pages but it is a surprisingly easy read, and provides in-depth, but digestible information. Below are a few key points from the American Standard for Nursery Stock you may find helpful (along with a cheat sheet to get you to the appropriate tables in the larger document). However, we would HIGHLY recommend reading through the whole standard and having a copy handy. It truly provides an amazing wealth of info (there’s a great section on identifying unacceptable co-dominant leaders – a problem I’ve had first hand issues with!). This resource also provides all the information necessary when accepting or rejecting plant material that shows up at your site!

Read on below for a summary of what you will find in the standard. Or, if you’re looking for other ways to make specifying plants easier check out The Plantium!

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 General Standards for Nursery Stock Sizes:

  • Specifications must include plant size by caliper, height or width appropriate to the plant type.
  • Certain plants may be specified by container size (see below). ALL others should be specified with caliper, height or width.
  • Typically, plant size specifications should include only the minimum allowable plant size in that interval. In other words, if you specify a 2.5 in. caliper Type 1 shade tree you may get a tree anywhere up to a 3 in caliper because it references the 2.5 to 3 inch range for that type of tree. As long as you specify the minimum, you know you will not get a SMALLER tree.
  • Caliper is always measured six inches above ground or soil level for trees less than 4.5” caliper, and 12 inches above the ground for 4.5” or larger.

General Standards for Containers:

  • These are generally the only plants to specify by container size
    • Herbaceous perennials
    • Non-winter-hardy shrubs
    • Ornamental grasses
    • Groundcovers
    • Vines
  • Containers marketed and sold with a # designation must have volumes within the ranges shown in the ANSI standard in order to comply
  • Container classes #1 through #100 include the volume of a container that, if such a container were manufactured, would hold the equivalent number of gallons as the container class number. #1 = one gallon; #5 = five gallon and so on.
  • Nursery stock specifications that reference only an imperial volume measurement, such as “quarts” or “gallons,” are not in accordance with the Standard. I can tell you that our plant lists have gotten that WRONG for years!!
  • The SP designation refers to ‘small plant’ containers. #SP4, for example, is a 4 inch container, or “quart” container. This designation goes from #SP1 – #SP5 and should reference square or round.
  • Container grown nursery stock shall have a well-established root system reaching the sides of the container to maintain a firm ball, but shall not have excessive root growth encircling the inside of the container (the same holds true for roots in ball and burlap!).


Root Bound

Container Growth Gone Wrong – Root Bound Tree

Tree B&B

When Done Right – A Thing of Beauty


Shade and Flowering Trees:

  • There are FOUR types of shade and flowering trees identified in the standard with the following associated specifications tables
    • Type 1 – Page 15-16
    • Type 2 – Page 17
    • Type 3 – Page 19
    • Type 4 – Page 21
    • Multi-stem and Shrub Form Trees – Page 24
  • Multi-stem tree specifications should include a minimum number of stems. If none is specified, 3 will be assumed.

Deciduous Shrubs:

  • There are THREE types of deciduous shrubs identified in the standard with associated specifications
    • Type 0 – Page 28
    • Type 1 – Page 28
    • Type 2 – Page 29
    • Type 3 – Page 30
  • Plants may not meet plant size specification or minimum number of canes at time of shipment at certain times of the year, but would be expected to reach the plant size specification and minimum number of canes during the first growing season after shipment.

Coniferous Evergreens:

  • There are SIX types of Coniferous Evergreens identified in the standard with associated specifications
    • Type 1 – Page 32
    • Type 2 – Page 33
    • Type 3 – Page 34
    • Type 4 – Page 36
    • Type 5 – Page 38
    • Type 6 – Page 40
  • Coniferous evergreens will also be described by their shearing:
    • Natural: (showing the form natural for the species)
    • Semi Sheared (sheared when plant is young to maintain symmetrical shape)
    • Sheared (pruned regularly to retain a symmetrical shape)
    • Altered Form (Can you say POODLED!!)

Broadleaf Evergreens:

  • There are SIX types of Coniferous Evergreens identified in the standard with associated specifications
    • Type 1 – Page 42
    • Type 2 – Page 44
    • Type 3 – Page 46
    • Type 4 – Page 48
    • Type 5 – Page 50
    • Type 6 – Page 52

Additional information in the standard provides specs for young plants, roses, palms (and other bare root stock), fruit trees, bulbs, corms/ tubers, and understock/seedling trees and shrubs.

Now, armed with this great information, you can confidently go forth and specify!

Also, check out these other great articles regarding considerations on transplant size:


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Fun Facts: Planting Design ‘at Altitude’

This short article attempts to bring some clarity to the complicated discussion of “designing at altitude.”

Everyone acknowledges that elevation plays a role in plant growth. The most widely known and visible example of this is the phenomenon known as Treeline. (Check out this article for a great explanation). But there is significant confusion among landscape professionals as to how and why elevation affects the plants you can grow in a cultivated setting. In fact, many commonly held beliefs are misconceptions or generalizations applied erroneously to all high elevation areas.

What truly changes as altitude increases, and how do these changes affect plants?

There are four factors that are universally tied to increased elevation:

  • Decreased temperature (generally)
  • Decreased atmospheric pressure
  • Increased exposure to overall solar radiation (on clear days)
  • Increased UV-B Radiation

All of these affect plant growth to varying extents. Decreased atmospheric pressure can translate to increased transpiration rates (the loss of water through plant leaves), however the lower air temperatures at high altitudes often negate this. Increased exposure to solar radiation can result in higher photosynthetic rates. Conversely, increased exposure to UV-B radiation impairs photosynthesis in many species of plants. And while exposure to both types of radiation increases with elevation, this is only on clear days, the number of which varies significantly by location, regardless of altitude.

Of the above elements, decreased temperature is the most universal change, and most likely the one that has the biggest impact on ornamental plant survival. Temperatures decrease by about 3.5 deg. F for every 1,000 feet in elevation gain. These cooler air and soil temperatures can affect many facets of a plant’s growth including seed germination, bud break, photosynthesis rate, flower season, and even pollen formation.

What isn’t a factor of elevation change?

Many other things attributed to increased altitude are not actually direct factors of elevation change, but rather location-specific environmental characteristics, such as:

  • Increased exposure to wind
  • Decreased available moisture
  • Shallow or poor soils

These are often applied generally to all high elevation settings, but in fact are highly dependent on the individual location.

Other environmental characteristics are actually a combination of latitude and altitude together, such as the perception of a shorter growing season. In central latitudes there is very little difference between the growing season at sea level and the growing season at a higher elevation. However, the closer you get to the poles, the more pronounced the difference becomes.

Sourcing plants from outside your elevation: Does it matter?

It is not a surprise that the same plant grown in a different area may appear different. Distinct temperature ranges, soil types, humidity, etc. will cause a plant to display different characteristics as it adapts to its environment. Species sourced from alternate regions may even have divergent genetics. An example provided by the Larimer County Ag Extension is Redbud (Cercis canadensis). Trees from seeds collected in northern areas (Wisconsin, Minnesota) are much more hardy than seeds collected from warmer climates like Oklahoma or Texas.

Regardless of elevation, it is always a good idea to source your large material from a climate comprable to that of your project. The years the plant has spent adapting to a similar climate will prepare it for successful establishment when you transplant it at your site. Compounding the stress of transplant with the stress of a wholesale change in growing environment will only increase the chance of death or failure to thrive.

The Takeaway:

At its core, successful establishment of ornamental plants depends on day length, season length, high and low temperature tolerance, and moisture/nutrient availability. The environmental factors that your site experiences must be taken into account when creating a design and selecting plant material, but elevation does not need to be added as a mysterious compounding factor.

If you think a plant can withstand your temperatures, moisture level, water, and exposure: give it a try, and let others know what you find out!

References: (Georgraphical variation in Sitka spruce productivity and its dependence on environmental factors)

Larimer County Ag Extension