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

 

Designing with Bulbs

We’ve all read some great articles about designing with bulbs (and corms) so why not keep the discussion going? Designing with bulbs can be daunting. Visiting the botanic gardens in spring nearly blinds us with the glory of huge swaths of spring bulbs. Vast beds of daffodils, crocus and tulips are the sure sign that spring has sprung. A bed of crocus dusted with snow is an iconic image of early spring. Now let’s focus our attention on some other aspects of designing with bulbs, year-round interest and designing to specific bloom heights.

5177_WPFL_Eremurus-himalaicus-WMC_001Dahlia 'XXL Veracruz' AZTEC

The opportunities presented by designing with bulbs can be taken advantage of year-round with a little planning and great execution. Gladiolus and Dahlias can bring in a huge color punch during the mid-summer to late summer in warmer climates and similarly Allium and Autumn Crocus in colder climates. Similarly, lilies can provide a tremendous amount of foliar interest in the early summer months and then finish the season off with splendid color in late summer and even through the fall. The first step is to sort through the vast array of choices in bulbs and corms and remember what you are trying to achieve. Here a sampling of a season-long list for a garden in zone 6a, that’s scented, and attracts bees, hummingbirds, and butterflies. This short list from The Plantium yields plenty of choices to keep you thinking about designing with bulbs all season long! There are so many more to choose from!

Bulb Flowering Season

The next consideration is careful planning around bloom height. This same list now includes plant (foliar) height vs. actual bloom height. Not planning for the bloom height of late blooming bulbs is a common mistake. Some height variations will be minimal but some can be more than a foot or even up to 4’! Check out the Foxtail Lily. Many of these bulbs are not known for lush foliage so you can place them further back in the garden (than you might normally based solely on foliar height) with other perennials or shrubs around them. This leaves their bloom to surprise us when the time is right!

Bulb Flower Heights

Find Your Inspiration

Find Your Inspiration

Where do I find my inspiration for designing beautiful gardens year after year? Ten years ago I first witnessed a living wall at the Chelsea Flower show in England and after lots of dreams and drawing boards I finally got to create my first living wall last summer 2015 right here in downtown Aspen, Colorado.

in·spi·ra·tion

  1. Noun: the process of being mentally stimulated to do or feel something, especially to do something creative.

Inspiration and trends in gardening can start from an article in a magazine, a student’s concept while studying at University or at the array of garden shows that are held all over the world.  This is where I find my best inspiration.

A particular favorite garden show of mine is the Chelsea Flower Show in London, England – where all of the best and greatest designers in the world all gather over ten days and meet to show off their latest creations. It was here at the Chelsea Show I first saw a living wall and marveled at this enormous structure covered in plants.  Without seeing the vision of the designers before me – I would never have been inspired to cover a concrete wall in flowers!!!

These shows provide not just single inspiration (i.e. living walls) but everything from solar paneled irrigation, new types of plants (cross pollinating a rose and a daisy!) and even animal habitats. Creative urban wildlife habitats are another huge trend that I first saw at Chelsea as well as water features created from household gray water. Show and display gardens are designed to impress at garden shows so if you really want to see what’s at the cutting edge of gardening then you’d better hit the show road.

Garden shows are featured all over the world – Holland, Japan, England and America and feature world class innovators and designers who create show gardens that win awards and prizes and wow us all. Depending on the size of the show local, national and international celebrity gardeners such as Piet Oudolf (a particular favorite of mine) will unleash new planting schemes and plant combinations that are created in an environmentally conscious way to thrill and tantalize us all. By witnessing world class designers and their incredible ideas we can all take small parts of this back to our own backyards. Not that you have to build a living wall in your own back garden but rather maybe, just maybe someone else’s genius idea displayed at your local gardening show might just be the inspiration for your own garden designs!  After all we are all inspired by others.

Here is a selection of inspirational gardens that have moved me over the years.

Happy Planting!

Arabella Beavers, Busy Beavers Gardening

https://www.facebook.com/Busy-Beavers-Gardening-LLC-201131763257382/?fref=ts

Aspen, Colorado

All photos Copyright 2016 Arabella Beavers

Garden Inspiration

Beautifully designed stone wall also serves as urban wildlife habitat.

Garden Inspiration

A living wall seen in indoor and outdoor applications.

Garden Inspiration

This greenhouse should blow your mind!

Garden Inspiration

A living tower gives entirely new meaning to vertical planting.

Garden Inspiration

Xeric Mediterranean style in any climate.

Garden Inspiration

The beauty of hundreds of Clematis!

Garden Inspiration

A ‘plethora’ of lavender from many different growers!