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

Xeriscape: A to X

Welcome, Soon-To-Be Xeriscape Experts

Even if you have never heard of xeriscape before now, this article will provide you with all the info necessary to confidently execute a xeriscape project, whether its for your client or in your own back yard.

For those of you already familiar with the concept of Xersicape, don’t worry! This post covers not just the basics, but also gives great details on elements of xeriscape with which you may not have been familiar.

 

What is Xeriscape?

zeroscape crop

Lets get this out of the way first. It is not ZEROscape! “Xeriscape” is a combination of the Greek word “xeros,” which means dry, and the word “landscape.” “Zeroscape” is a common mispronunciation and misconception that we will discuss more later in the article.

Xeriscape Definition:

Xeriscape is a system of principles to create gardens and landscapes that reduce, or even eliminate, the need for additional irrigation. Xeriscape is not a garden style, and it does not mean just rocks! Xeriscape principles can be applied in any region across the world.

Xeriscape History:

While Coloradans did not invent water-conscious landscaping, we did invent “xeriscape!” Denver Water, Colorado’s oldest and largest water utility, coined the term ‘Xeriscape’ in 1981 as part of an effort to make water-wise landscaping a recognizable concept. At the same time they assigned 7 simple, accessible principles to xeriscaping so that anyone creating or maintaining a landscape could incorporate water-conserving techniques.

Xeriscape Principles:

  1. Plan and design
  2. Plant zones
  3. Alternative turf grasses
  4. Soil amendment
  5. Mulch
  6. Efficient irrigation
  7. Maintenance

What is NOT Xeriscape?

Misconceptions

Xeriscaping has been growing in popularity across the country as a way to utilize water resources more sensibly, and create landscapes than can be beautiful and resilient in periods of drought. But misconceptions consistently stand in the way of many people’s acceptance of the concept.

 Misconception 1: Xeriscape is Just Rocks

Not ROcks

As we mentioned before, xeriscape is NOT “zeroscape”. Xeriscape does not mean replacing your lawn or traditional landscape with rocks or hardscape! A field of pavement or gravel does just about as much for your property value as dead grass, and provides even less environmental benefit.

Instead, xeriscape emphasizes:

  1. choosing plants adapted to the rainfall of your region
  2. grouping plants with like water needs
  3. reducing (not eliminating) turf area
  4. using efficient watering techniques to achieve beautiful landscapes

 Misconception 2: You Can’t Have Lawn

Xeriscape does not mean no lawn.

As the popular saying goes, xeriscape does not mean lawn-less, it just means less lawn.

We LOVE our lawn here in the US. While the total square footage of lawns is decreasing, a study done by a NASA scientist in 2005 suggests there are “three times more acres of lawns in the U.S. than irrigated corn” (approx. 49,000 square miles of lawn), which makes it the largest irrigated “crop” in the US by surface area. The lawn has been soliloquized as an aesthetic expression of Manifest Destiny. Whole collegiate majors are devoted to turf grass. This American love of lawn is one of the most prominent barriers to adopting xeriscape principles in residential landscapes.

But fear not! You can still have that patch of emerald green grass for your kids to play on, or even just for your dog to whizz in, by:

  1. carefully placing turf grass only where it will be used
  2. choosing grass species best suited to your climate
  3. watering efficiently

 Misconception 3: Xeriscape is all cactus and pokey things

Xeriscape is not just cacti

 

Just as xeriscape does not mean replacing your lawn with rocks, it does not mean only planting cacti. (Although check out this article to see how cacti can be beautiful in any landscape!)

Xeriscape entails selecting plants of all kinds that will thrive without requiring much additional irrigation. It is important to remember that this is based on the part of the country in which you are planting. Xeriscape plants for Colorado, which receives an average of 15 inches of precipitation per year, will be different than those for Arizona at 8 inches of precipitation, or Florida at 64 inches!

No matter what part of the country or state you live in, there is a large palette of plants, yes even non-pokey ones, which you can use to create a beautiful xeriscape in any style.

Misconception 4: Xeriscape Yards look Shaggy and Unmaintained

Xeriscape yards can be beautiful

The truth is that you can achieve almost any design aesthetic, from formal to cottage to meadow, using xeriscape principles and a combination of native and regionally adapted plants. There are myriad reasons to want a beautiful yard, from HOA requirements, to property values, to the all-important question “What will the neighbors think?!” When many people envision xeriscape, even if they aren’t thinking cactus and gravel, they think of a tangle of unkempt natives.  But in fact, a well-executed xeriscape project can be the envy of the neighborhood!

 

Why should I consider Xeriscape?

Beautiful Landscapes without the Extra Water

Yard Drought

The EPA estimates that outdoor water use (landscape irrigation, etc) accounts for 30% of our national water consumption. CSU estimates that in the arid west it can be as much as 55% to 60% of household water use, with most of that going on lawns.

Why is this important?

Whether or not you live in an arid region, droughts happen somewhere in the country every year. During droughts outdoor watering can be severely curtailed, and it can take a heavy toll on the beauty and diversity of home and public landscapes. By planting plants that are already adapted to the natural rainfall of your region, and that are also drought tolerant (can maintain their vigor during periods of less than normal rainfall), you can have a landscape that thrives even during water shortages.

A five-year study (YARDX) of 357 residential landscapes conducted by Metro Water Conservation, The Bureau of Reclamation, and 7 Colorado front range municipalities worked to quantify the water savings of xeriscape. It found that homes which utilize xeriscape principles, halve their current lawn, and plant ¼ low water use plants and ¼ medium water use plants reduced their outdoor water usage by an average of 30% and up to 50%.

Time and $$$$$$!

Water Value

Unless you are fortunate enough to be on a ditch or well, reduced water consumption directly results in money savings!

Another financial benefit of xeriscaping is increased home value. A study by the Virginia Cooperative Extension found that a beautiful landscape increased perceived home values among buyers by an average of 11%, and the numbers were highest for landscapes that were not exclusively lawn.

Finally, xeriscape requires less input of time and money (fertilizing, seeding, mowing, aerating, etc) than a lawn of comparable size. Why not free up those weekends for something other than lawn maintenance?

Let’s Get to Xeriscaping!

Now that you have a basic idea of what Xeriscape is and is not, and some idea of the benefit, lets dive deeper into the principles of xeriscape and how to take a xeriscape project from beginning to end!

Principle One: Plan and Design

Understand What You Want

As with any project, you’ll get a better product (and save a bit of money) if you take some time to flesh out the goals first. The initial design process for a xeriscape project is just like the process for any other landscape project:

  1. Create the program.
  2. Pick a style. As mentioned above, xeriscape is not a garden style. You can achieve any landscape style you like using xeriscape principles!
  3. Create a plan of hardscape and other improvements, and block out planting areas.

Principle Two: Plant Zones

Definitions:

Low water use plants – Plants that require no additional irrigation after establishment, based on the region’s rainfall.

Medium Water Use Plants – Plants that require a moderate amount of irrigation after establishment, based on the region’s rainfall. (One deep watering every 4 days in warm weather)

Step 1: Establish your Water Use Zones

Although xeriscape emphasizes plants whose water needs are in line with regional rainfall, this does not mean you can’t have higher water use plants and lawn in your landscape. Xeriscape groups medium- and low-water-use plants together maximize watering efficiency.

Spend your water where you spend your time

  • Focus higher-water-use plants in high-use areas such as decks, patios, paths, etc.
  • Also place higher water use plant in areas where water typically collects such as adjacent to downspouts, in low lying areas, or along ditches or ponds.
  • Concentrate lawn only where feet will be using it, and make it only as big as you need.

A good rule of thumb for many back yards is 1/3 low-water-use plants, 1/3 medium-water-use plants, 1/3 lawn. If feet aren’t using the front lawn then don’t include it! An appropriate front yard is more like 2/3 low-water-use plants, 1/3 medium water use plants. But the more you skew your ratios to low water use plants the more water you will save!

Based on your design, decide where to cluster water uses and where your lawn will be located. This will correlate directly with the irrigation system design, if one is being installed.

Xeriscape water use zones diagram.

Step 2: Pick Some Plants!

After you establish your water use zones, it is time to flesh out the planting design. Appropriate plant selections are not only key to saving water, but also to completing your design vision. This is where criteria-based plant design can really be an asset. Take some time to review this great article on how to make the best plant selections using criteria-based plant design, then use water use as one of your primary plant selection criteria.

Each state and region has resources available to help individuals and professionals choose plant material for xeriscape, many of which are easily searchable online. Several states have programs such as Plant Select, EarthKind, and Texas Superstar (part of EarthKind), and that help identify and introduce the best plants for specific regions. Or check out this list of resources from the EPA to get you started.

 

Principle Three: Alternative Turf Grasses

Alternative Turf Grasses vs. Turf Grass Alternatives

There are two distinct ways to treat lawn areas in xeriscape designs, based on your desires and the amount of foot traffic your lawn will receive.

If you want a true lawn for entertaining, playing, etc. explore your best regional alternatives to standard bluegrass. There are many varieties that will provide you a beautiful lawn with 30% to 75% less water.

If you like the idea of a space that you can occasionally walk across or just put a bench in you might consider turf grass alternatives. There are many that work well in each region and that require significantly less water and maintenance than traditional turf.

Xeriscape thyme lawn

Principle Four: Soil Amendment

We all know that the health of the plants in our landscapes largely depends on soil quality. So before you pop those new plants in the ground remember that almost all types of plants will benefit from the use of compost! Organic matter in compost helps sandy soils retain water better, and helps clay soils release water more effectively and drain more freely. In addition, compost will help replenish the nutrients in soil without the need for fertilizer.

The standard recommendation is 1 to 2 inches of compost over the area to be planted, tilled to a depth of 4 to 6 inches.

 

Principle Five: Mulch

Now the plants are in and looking beautiful, but don’t leave that ground between your new plants exposed! Mulch is a crucial part of any landscape or a variety of reasons. First, it looks much better than bare dirt.

Second, and more importantly, mulch:

  • keeps your soil in place
  • keeps your plant roots cool
  • prevents soil from crusting
  • minimizes evaporation
  • reduces weed growth

Organic and inorganic mulch.

Mulches come in two types: organic, such as fiber, bark, pine needles, etc; and inorganic, such as rocks and gravel. Both types serve the same ultimate purpose and have their own advantages, so your ultimate choice should depend on the desired landscape style.

Organic mulch should be applied 4 inches deep, and inorganic mulch should be applied 2 inches deep.

Principle Six: Efficient Irrigation

The purpose of xeriscape is to reduce the amount of water you need to apply to your landscape. In some cases, you can even eliminate watering altogether! But almost no freshly-planted landscape can thrive in its first two years without additional water.

Establishment Irrigation

Because they have not established a mature root system, transplanted plants almost always require supplemental irrigation during for the first two years after planting. This is true for all transplanted plants from trees to groundcovers. If done correctly, providing your landscape with some additional water during these first two years ensures long-term vigor and the growth of a healthy root system.

While your plants will need slightly more water in these first two years, remember not to kill them with kindness! Keep in mind the overall water use requirements of your planting areas (your plant zones) Low water use plants need only small amounts of supplemental water in their establishment phase, whereas your medium-water-use plant areas will need more.

There is a Wrong Way to Water

Whether manual or automatic, the most important things to remember about irrigating any landscape, but especially xeriscape are:

  • Respect your zones
  • Choose the right delivery method
  • Water at the right time

Zones

Your xeriscape will only use less water if you give it less water! Don’t throw your work creating plant zones out the window by watering everything equally. If a new irrigation system is being included in your project make sure it is zoned according to your water use plan.

Water Delivery Method

Xeriscape can be irrigated efficiently by hand or with an automatic sprinkler system. Regardless of how you water, it is important to choose the most efficient water delivery method.

Fundamentally, the best irrigation:

  • Waters deeply and slowly, allowing water to soak in rather than run off.
  • Delivers large drops of water close to the ground, thus reducing water loss due to evaporation.

Avoid watering systems that throw water high in the air or release a fine mist.

Below are common recommendations for each planting area type:

  • Grass: Use gear-driven rotors or rotary/high-efficiency spray nozzles that have larger droplets and low angles to avoid wind drift.
  • Trees, Shrubs and Perennial Beds: Use low sprays, drip lines or bubbler emitters

For much more in-depth information about watering systems and calculations check out this article from the “Water – Use It Wisely” conservation campaign.

Examples of efficient irrigation methods for xeriscape.

Timing

The following principles apply to frequency and duration of watering your xeriscape to maximize efficiency and create the most robust root systems:

  1. Never water between 10 am and 6 pm, when water loss due to evaporation will be the highest. Watering late at night or early in the morning reduces this loss, and gets the plants ready for the day.
  2. Water more deeply but less often. Frequent shallow irrigation encourages shallow, less vigorous root systems, and leaves the plant more susceptible to drought stress. Conversely, reducing watering frequency and making sure that the water penetrates deep into the soil encourages more vigorous and robust root systems in all your plants, but especially trees and shrubs.
  3. Water-rest-water. As part of allowing water to penetrate more deeply, water each area in intervals. By taking a “water-rest-water” approach, you allow more water to soak into the root zone, and loose less to runoff.

Weather

Don’t forget that you are not the only source of water for your plants! If it has been rainy, cool, or cloudy, your plants will have taken up and lost less moisture, and will therefore need less irrigation. If you have an automated irrigation system, install rain and soil moisture sensors to prevent excess irrigation. If you are watering by hand, you can get tensiometers or use the time-honored “poke a finger in the soil” trick.

Don't be this guy.

Principle Seven: Maintenance

Depending on the design style, xeriscape can be very low maintenance. But we all know there is no such thing as a no-maintenance landscape!

If you have chosen to include it, the lawn will likely still require the most input of time and materials in your xeriscape. Turf requires spring and fall aeration along with regular fertilization every 6 to 8 weeks. To reduce the amount of weeds in your lawn, and reduce its water needs:

  • keep the grass height at 3 inches
  • allow the clippings to fall.

Incidentally, according the NASA study, this also dramatically increases the carbon storage capacity of your lawn!

Aside from the lawn, there are the normal chores of weeding, pruning, trimming, etc that are inherent in any landscape. The intensity of these tasks depends most on your landscape style, but don’t forget to compost the yard waste for reincorporation into your landscapes each fall!

 

Ta Da! You’re an Expert

Now you know: xeriscaping is not mysterious or difficult. With a little bit of forethought, you can have a beautiful landscape and use less water while you’re at it! Go forth and xeriscape.

 

Other Resources

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

 

Using Denitrifying Plants in the Landscape

Turns out we have an addiction in this country. “Call it the nitrogen fix. It is like a drug mainlined into the planet’s ecosystems, suffusing every cell, every pore — including our own bodies.”1 In response, some jurisdictions (apparently finding dealing with addiction at the source – i.e. agriculture, wastewater, feed lots, poor landscape practices, etc. too difficult) are requiring the end user of non-potable reclaimed effluent to utilize only denitrifying plants in the landscape. Their theory being that if the ornamental plants can take up the nitrogen, then problem solved.

This discussion of overabundance of nitrogen in our water and soil could get really scientific, really fast (and unfortunately make for very dry reading) so instead I’m going to keep things pretty simple and straightforward and provide some great resources for seeking additional information.

The nitrogen problem. “Over the last century, the intensive use of chemical fertilizers has saturated the Earth’s soils and waters with nitrogen. Now scientists are warning that we must move quickly to revolutionize agricultural systems and greatly reduce the amount of nitrogen we put into the planet’s ecosystems.”1 Excessive nitrogen leaches into waterways, feeds algal blooms and contributes to eutrophication of water systems….. effectively starving plant and aquatic life of oxygen. It can even starve our children of oxygen, known as Blue Baby Syndrome, as a result of nitrogen contaminated drinking water.

The good news. Nitrogen is an inorganic compound which, unlike other macronutrients, can be turned to gas and released into the atmosphere. More good news. This means that the use of denitrifying plants can be addressed via phytometabolism in a relatively short period of time and presents good opportunities for field application.2 “Since all plants use nitrogen and support denitrifying bacteria, any kind of plant can provide some form of nitrogen remediation from soils and water. However, the method that provides the quickest remediation tends to be a system that includes plants with very high growth rates and evapotranspiration rates. Nitrogen is used up quickly, or the plant acts like a large reactor, priming the soil bacteria for speedy conversion of the nitrogen into a gas. Plants species that produce a lot of biomass have been those most successfully used in studies to remove high levels of nitrogen in soils and groundwater.”3 Some would then argue for the use of bluegrass and other fast growing turf, but studies have shown that a mixed species landscape will produce a more diverse microbial soil, and therefore denitrify faster via plants AND bacteria.

Finding the right plants. While in no way an exhaustive list, the book Phyto: Principles and resources for site remediation and landscape design, suggests a brief list of high biomass plants such as Bambuseae, Brassica juncea, Brassica napas, Cannabis sativa, Linum usitatissimum, Panicum virgatum, Populus, Salix and Sorghum. Additionally, some high evapotranspiration-rate plants include Alnus, Betula, Eucalyptus, Fraxinus, Populus, Salix, Sarcobatus vermiculatus and Taxodium distichum. Again, while not an exhaustive list one thing to note is that these tend to be high water use species. In a large scale remediation setting this is desirable (because you are purposefully applying large amounts of contaminated water), however, it tends to fly in the face of end user goals in the ornamental landscape that are working hard to reduce overall water consumption.

Unfortunately, it would seem that municipalities, especially in drought plagued areas trying to encourage water reuse, may end up further discouraging effluent reuse with these unnecessary regulations and may find themselves dealing with unintended consequences, such as forcing the use of plants that require even more water to both thrive and denitrify the soil. It is clearly a discussion worth continuing.

 

I’d like to thank Kate Kennen for the amazing information gathered from her book for this article. Kate is always an inspiration and this book is an INCREDIBLE resource for all practical applications, large or small, for phytoremediation and productive landscapes. It is a must read!

Find Kate here….  http://offshootsinc.com/

Find her book here…. https://www.amazon.com/Phyto-Principles-Resources-Remediation-Landscape/dp/0415814154

  1. Fred Pearce. Copyright 2009. http://e360.yale.edu/mobile/feature.msp?id=2207
  2. Kate Kennen and Niall Kirkwood, Phyto: Principles and resources for site remediation and landscape design. Routledge, 2015. Figure 3.1, Page 63
  3. Page 128

Pick Plants with Emotional Intelligence

Selecting the right plants for a design regularly becomes one of the most time consuming portions of a design project for me.  Like all designers, I have my list of go-to plants; the tried-and-true plants that thrive and provide a lot of visual interest.  But every landscape calls for unique plants, whether for a unique function or to highlight a specific spot.  When you are trying to pick plants…. those few perfect plants, from the thousands of possibilities, it is easy to have time fly by and, before you know it, you have skipped lunch (maybe even dinner) and still have to select more plants.

Of course, the more conditions you add to a specific selection, potentially the more amount of time it takes to make the right choice.  This is especially true when you are working in less familiar territory.  If you need a Mediterranean garden, I can rattle off a list of plants a mile long that would fit.  But what about when that garden is going to be located adjacent to a disused rail line, and I need plants that will help detoxify the soil in addition to looking great?

This is where The Plantium will step in.  For the last couple of months I have been speaking with landscape architects and designers, environmental planners, urban planners, conservationists, and many others, asking the question: What environmental factors impacting plants do you regularly consider?  All of these responses are being used by The Plantium to improve their database of plants so that the selection process will be easier, no matter the situation.  So when you need to know what plants will thrive along a disused railroad track, you can search for plants that are tolerant to copper, arsenic, and petroleum products, three of the most common pollutants along rail lines.

What are some of the most common environmental factors design professionals consider when selecting plants?  There are the apparent ones (and ones that The Plantium already supports) such as sun exposure, water requirements, and soil conditions.  Some of the other commonly mentioned factors were:

  • High wind conditions
  • Heavy metal tolerance
  • Pollution remediation
  • Intermittent water inundation
  • Nitrogen and phosphorous uptake
  • Air pollution tolerance
  • Early establishers in disturbed landscapes
  • High UV radiation tolerance
  • Pine needle and leaf-litter tolerance
  • And many others

Some of these factors are certainly specialized to specific design sectors, but others are ones that designers need to deal with on a regular basis.  For instance, in Northern Utah we receive approximately 15% more UV radiation than at lower altitudes.  Several plants have foliage damage at our elevation if they are planted in the direct sun.  This is just one example of why I am excited to see these factors added to The Plantium’s database.  Look for that in future updates!  Until then, happy planting!

Check out the entire white paper. CLICK HERE

Guest Author:

Benjamin George, Ph.D.
Assistant Professor
Landscape Architecture & Environmental Planning
Utah State University