Soil Depth and Plant Selection

Minimum soil depth for plant growth is a frequent subject of discussion of late and while you cannot search The Plantium based upon soil depth, we thought we’d gather some information to assist in your criteria based plant designs!

Let’s first look at the question at hand. As designers and installers we are asked to create landscapes in all sorts of conditions. Often these conditions are challenging and not necessarily conditions that plants might face in their natural environments. That said, we have all seen these images at some point in our lives…. the beautiful and resilient plant that appears to be growing happily, in what appears to be NO soil depth AT ALL!

 

 

 

 

 

 

 

 

 

For those looking for answers regarding bed construction and just soil depth in general, let’s send you to one of our Plantium brands for some fantastic basic information regarding bed construction in the field.

https://www.provenwinners.com/learn/make-your-bed

Soil depth for OPTIMAL plant growth in more challenging situations such as green roof conditions, large planters, tree wells, etc. is dependent on four main factors. These factors are proper drainage, proper plant selection, plant longevity, and soil depth to plant height ratio. We’ll discuss these factors in this order because the very last issue you should be considering in your plant design is soil depth. If you have not addressed the first three issues in your bed design then regardless of soil depth, plants will not thrive.

Proper Drainage

Whether your planting bed is in the lawn, green roof or contained planters, 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 the plants. There are many ways to tackle drainage and all are dependent on the design situation. Working closely with the horticulture team is the best way to find an effective drainage solution.

Proper Plant Selection

Let’s look at those tough little plants growing in the cracks and crevasses! You need to keep in mind the type of plant you are specifying when dealing with challenging planting situations. 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 more sensitive plants, it is likely that those plants will struggle. Also, remember that as the soil profile for any plant is constrained so will the plant’s natural habit be constrained. Street trees planted in minimum soil volumes will never reach the full mature height or width that they would under optimal growing conditions.

 

 

Plant Longevity

Planting designs are being designed and installed with a maximum 20 year life span. A controversial statement, perhaps, so feel free to challenge it! It appears long gone are the days of an Olmsteadian landscape that appreciates with time and just barely reaches its full glory at 20 years. Here at The Plantium we vehemently disagree with this trend and firmly believe that criteria based plant selection can reverse this trend. Better plant choices! We’d love to hear your comments on this issue!

All that said, green roof and enclosed planter situations pose different challenges. Small planters and shallow green roof systems need very carefully management to maintain soil health and ultimately plant health. The shallower the soil profile the more quickly that soil will be depleted of nutrients and micro-organisms crucial to the plant’s health. If a refresh of the plant material (and soil) is planned over time, then shallower soil profiles can be a great fit. If the design contemplates trees and shrubs that are intended to grow to maturity over time, then a more significant soil depth should be considered.

Soil Depth

On to the question at hand. Let’s simplify the soil depth for optimal plant growth under container type situations into the following categories. Again, exact soil depth is probably debatable by many so we welcome other thoughts from our expert crowd!

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

 

Maintenance

Lastly, on-going maintenance is the greatest issue facing these planting designs. Over-watering is perhaps the most frequent maintenance faux pas committed against our container plants. Carefully working with the maintenance team is critical to head off this issue early on.

Happy Planting Y’all!

 

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!

Background

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.

Conclusion

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!

References:

  1. http://www.academia.edu/4110694/Politics_of_Pollen_Article Copyright 2001, Tom Ogren
  2. http://www.webmd.com/allergies/news/20000427/high-pollen-linked-death#1
  3. http://www.bbc.com/news/world-australia-38121579
  4. https://blogs.scientificamerican.com/guest-blog/botanical-sexism-cultivates-home-grown-allergies/
  5. http://www.healthyschoolyards.org/

Image References

https://commons.wikimedia.org

Designing with Dog Friendly Plants

Ever wonder how we get our yards, parks, and streetscapes to be ‘dog friendly’? As in, how do we design a urine and trample resistance landscape filled with dog friendly plants? Well, let’s start with thinking about some alternative groundcovers that can take a little beating. These are plants that can be used as an alternative to turf. Turf alternatives can save water AND help fight off the brown patches that come with a ‘dog heavy’ landscape. A couple good examples in the attached pdf include Elfin Thyme and Ajuga. These are just two great choices, but you can always use your filter criteria and select low growing plants that can withstand foot traffic. In The Plantium’s filter criteria you’ll find the foot traffic filter under ENVIRONMENT.

The second issue is urine resistance. While this is NOT a filter in The Plantium, the attached pdf has some tried and true choices that can withstand the excessive nitrogen content in dog urine. Again, not an exhaustive list but a good start. Remember to also consider any plants that are TOXIC to pets and avoid those. Sending your little furry friend to the vet would definitely NOT be considered dog friendly plants! For those Plantium users, this is a filter criteria under WILDLIFE. For those of you not yet in The Plantium you can visit the ASPCA site (Plantium’s filter criteria is WAY easier, though!) 🙂

Lastly, and perhaps most obvious would be water. The faster you can wash away any leave behinds from the doggie visitors, the better chance of avoiding the burn spots, so let’s take back those brown patches and get into our dog friendly plants!

Dog Friendly List

https://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants

 

Understanding the Importance of Tree Root Structure

Perhaps the importance of tree root structure seems obvious but oftentimes our misconceptions related to the root structure can compromise both the health of our trees and the health and integrity of the landscapes around these trees. Making good species choices above ground AND below ground is the first step in having trees that survive and thrive in the landscape. We have all seen the potential damage done by tree roots as they crack sidewalks, clog sewer lines, and penetrate foundation walls. The unfortunate consequence has been that trees are becoming a consumable ingredient in the landscape, living 20 years at best and then being replaced. However, with knowledge of species choice and a great understanding of what root systems need, we can reverse this trend.

One of the first misconceptions is that particular species of trees will have predictable root structures and while this may be generally true in ideal growing conditions, huge variations occur based upon 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 continue root growth above that layer of compaction. This is very typical in urban situations where compaction and poor drainage is a serious issue. Similarly, with a perched or high water table. However, the root structure of trees growing in sandy soils can grow to great depths.

A second misconception is related to the overall size of the required root structure for a healthy tree. Tree protection requirements in most jurisdictions require only protection of the tree root structure to the dripline but as you can see below 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

Again, size of a root structure will be depending on the tree species but more importantly soil conditions and access to resources. If a tree species would normally grow a tap root but runs into heavily compacted soil, it will simply continue the growth out instead of down. When designing for trees in constrained spaces it is important to think about your ‘container’ below ground. Where are the barriers on the container and what will the tree roots do once they encounter those barriers?

Certain species of trees are just considered a ‘no-go’ when designing in constrained spaces such as urban plantings, small backyards, and near sidewalks and utilities. These species are off limits for different reasons. For example, populous, ficus, Silver Maple, and poplar have aggressive flat (meaning they are growing mostly flat and shallow to the ground) primary root structures. Whereas, other populus, salix, American Elm, bamboos and robinia are generally off limits simply because of their love of water and how prolific their root structure is. Remember that roots are going to grow where they are welcome! Oftentimes the issue with sewer lines, water lines, or ditches is that there is a small break in the line already and the nearby roots simply make a beeline for the moisture!

The best defense to damaging tree root structures (in addition to making great tree choices in the first place) is to define and maintain a fantastic ecosystem for the root structure so it need not go far for everything it needs. Because the majority of the root structure is taking up nutrients and water in the top 6-12” of soil, it is imperative to remember that anything done within the dripline and say 2-4 times greater than that is where the tree root structure will get everything it needs (or doesn’t). Herbicide applied in this area can have an immediate effect on a tree.  While this may be up for debate, fertilizer spikes, etc. are unnecessary for most trees and fertilizer, mycorrhizae amendments, water, etc. can all be applied to the surface under the tree.

Using structural soil, Silva Cells, root barrier, etc. are all great tools in constructing the correct ‘container’ for the tree’s root structure. If these are not required in urban settings where you work, consider doing some research and incorporating. This can take the longevity of an urban street tree from 5-8 years to 30+ years!

Lastly, consider covering larger areas of the root system with mulch when there is no snow on the ground but significant cold snaps are anticipated. These large areas of mulch can help with moisture retention and preventing roots from freezing during winters with vast temperature swings.

We’ve written a separate blog about planting under evergreens but really ALL trees will aggressively compete for the resources within the root structure of that tree. Being conscious of the additional resources needed both for the tree and for the plants under it is critically important. If the tree or the plants are failing, consider that one or both need additional resources – light, water, nutrients and oxygen.

  1. http://arnoldia.arboretum.harvard.edu/pdf/articles/1989-49-4-tree-roots-facts-and-fallacies.pdf Thomas O. Perry

 

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 your planting is successful is to use criteria-based plant selection – selecting plants based on specific desirable traits that support the aesthetic and environmental goals of the project.

Follow these 4 steps to OWN your next planting design project.

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!

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!

 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:

https://www.michigan.gov/documents/dnr/Influence_of_Tree_Size_on_Transplant_Establishment_277656_7.pdf

http://www.ncufc.org/uploads/Tree_Establishment_A_Review_of_Some_of_the_Factors_(Struve_2009).pdf

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:

http://aob.oxfordjournals.org/content/94/2/199.full

http://northernwoodlands.org/articles/article/why_is_the_treeline_at_a_higher_elevation_in_the_tetons_than_in_the_white_m

https://www.era.lib.ed.ac.uk/bitstream/handle/1842/283/worre3-4.pdf?sequence=2 (Georgraphical variation in Sitka spruce productivity and its dependence on environmental factors)

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.502.5473&rep=rep1&type=pdf

http://www.life.illinois.edu/ib/514/K%F6rner_2007.pdf

http://www.ext.colostate.edu/mg/gardennotes/143.html

Larimer County Ag Extension