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Soil Basics revisited

Understanding "the basics" of soil is no small matter.  One of the most basic problems with soil is compaction.  For many of my clients, the soil around their homes has been virtually ruined by what took place when their house was built or renovated.  Many (all?!) builders/contractors think of soil as dirt and make no effort to protect it or renovate it after they're finished.  Around here, most of the new development is infill development, so virtually the whole lot is disturbed - by tearing down the old house, by cutting down all the trees, by building an addition, by installing a pool.  Their machines churn across what might have been relatively undisturbed soil, often when the soil is saturated after a hard rain, creating ruts that are virtually impossible to correct.  They dig a new foundation and turn the existing soil-profile upside down in doing so.  What used to be subsoil is now on top.  When they're done, they flatten out the clay-ey subsoil, put back a couple inches of the "topsoil" that they allegedly scraped off at the beginning (is it full of weed seeds now?? has it been tested? what is its texture?  has compost been added?), throw down some "contractor's mix" el-cheapo grass seed and poof - there's your new lawn!  This is what we refer to as "urban soil".

Urban soils are typically inhospitable places for trees, other plants, and their oxygen breathing microorganisms.  Human activities, such as those described above, as well as grading and even foot traffic leave urban soils much more compacted than natural soils.  Typically 40-55% of the volume in a healthy forest soil consists of pore space.  This pore space consists of varying proportions of air and water depending on the weather.  With compaction, soil particles are pushed together and fill up pore spaces, so pore space in urban soils often goes down to 20-30%.

Soil compaction is generally estimated by measuring bulk density, which is the mass of dry soil divided by its volume, expressed in grams per cubic centimeter (gms/cc).  Compacted soil has less pore space and therefore higher bulk density.  Surface bulk density of most undisturbed soils ranges from 1.1 to 1.4 gms/cc, depending on the soil texture (clay, sand and silt fractions).  The bulk density of urban soils often ranges from 1.5 to 2.0 gms/cc, just slightly less than the bulk density of concrete (2.2 gms/cc)!  
The reduced porosity of compacted soils results in a lower water-holding capacity and reduced infiltration rate, so compacted soils produce much more stormwater runoff than undisturbed soils.  In many urban areas, pervious areas, like "lawns", produce almost as much runoff as impervious surfaces because they are so compacted. The reduced water holding capacity of compacted soils also renders plants more prone to drought and results in more extreme summer soil temperatures.
Compaction also drives oxygen out of these soils to suffocatingly low levels and oxygen-dependent soil microorganisms can no longer survive.  Without adequate soil organisms, urban soils generally have a lower organic matter content and lower nutrient retention than natural soils.  Soil compaction also limits root penetration and growth. Once soil bulk density exceeds 1.4-1.7 gms/cc (depending on soil texture), roots are no longer able to penetrate soil, and vegetation growth becomes limited.
That's one of the reasons that the "landscaping" your contractor installed before you bought your new house or moved into your renovated one has declined every year!



Spring 2014

Spring is here and it reminds me again of the rewards of planting spring-flowering bulbs in fall.  I've often said "It's the best hour you'll ever spend".  OK, maybe more than an hour.  If you have a deer problem, there are still plenty of spring-flowering bulbs that you could be admiring right now in your garden - daffodils, alliums, scilla, leucojum, galanthus ...You can also plant bulbs in large containers that are left outoodrs over the winter.  Here's some of what I installed in containers last year:

Narcissus 'Jetfire' flowers early and perks up containers.

Crocus chrysanthus 'Ladykiller'Crocus X vernus 'Vanguard'Tulipa kaufmanniana 'Heart's Delight'Allium X 'Graceful'


2014 Award Winners

The Perennial Plant of the Year is chosen by the Perennial Plant Association for its suitability for a wide range of growing climates, low maintenance, multiple seasons of interest and relative disease/pest resistance.

2014 Panicum virgatum 'Northwind' (Switchgrass) - a native warm-season grass with an upright form, blue-green leaves and gold fall color.  Like all Panicum (but different from some other warm-season grasses, the grass flowers are held just above the leaf blades.  For more details, check out the PPA website - it will tell you some of the great attributes of switchgrass for your garden.

Panicum virgatum 'Northwind'



The Cary Award is given to trees, shrubs and vines ("woodies")  with multiple seasons of interest and good disease and pest resistance.  It is administered by the Tower Hill Botanic Garden.  The purpose of the award is:

To inform home gardeners which plants would be good choices in their landscape, to instill confidence in the home gardener's selection, and to increase the diversity of plant material used by gardeners, landscape designers and architects.

The Cary Award has declared 2014 The Year of the Vine, and has selected three vines suitable for trellises, pergolas, porches, walls and anywhere else you need a climber.

Clematis X 'Betty Corning' (C. crispa X C. viticella) is a late, small-flowered clematis that was first discovered  in Albany NY in 1932.  It grows to about 6' tall and has nodding bell-shaped pale lavender flowers with recurved tips.  It flowers freely from June to Sept.  It needs only a little tying to grow well on a trellis, and can also be used as a ground cover if you're feeling adventurous - let it wind through your perennial border.  It should be pruned back in late winter-early spring, and can be cut back all the way to the ground without losing the season's flowers.

Clematis 'Betty Corning'

Actinidia kolomikta (Variegated Hardy Kiwi Vine) - a relatively fast-growing deciduous woody vine which grows to about 15 - 20', is grown mainly for its foliage and its bark.  It has variegated pink and white young leaves, fragrant white flowers in spring and peeling cinnamon-colored bark in winter.  This species has both male and female plants - both are needed for pollination.  The male plant has better leaf variegation - but 1' long greenish-yellow edible fruits are produced on the female plant in early fall.


Hardy Kiwi VineFlowers of the hardy kiwi are obscured by the foliage, but are fragrant

Wisteria frutescens (American wisteria) - a twining woody vine that grows to 40' or more - but the good news is that it is a less aggressive spreader than Wisteria sinensis (Chinese wisteria).  It flowers in April - May with fragrant, pea-like flowers in drooping 6" racemes, and may re-bloom on new wood in the summer.  Flowers give way to flattened smooth seed pods that ripen in summer.  The best flowering occurs in full sun.

Vines can take up to 3 years before flowering after they are planted, and they need regular pruning to control size and shape, as well as to encourage flowering.  Don't choose this vine if you're impatient or prune-o-phobic.  Also, take care where you plant it - it doesn't like to be transplanted very much.  Failure of vines to flower can be caused by death of the flower buds during a harsh winter, too much shade, plants being too young, improper pruning or over-fertilization (which favors leaf growth over flower-bud formation).  The two most common cultivars to be found in the Nursery trade are 'Amethyst Falls', with lavender flowers, and 'Nivea', with white flowers.

Wisteria frutescens 'Amethyst Falls'


All-America Selections honor new plants, including vegetables and annuals.  For 2014, one of their selection is Guara 'Sparkle White', a perennial in Zone 6 and above, that flowers all season.  It is a delicate plant with very clean white flowers that wave in the breeze above the foliage.  A really nice addition to the perennial border - or use it in your containers.  




The Society of Municipal Arborists has chosen Parrotia persica 'Vanessa' (Persian ironwood or Persian witchhazel) as the 2014 Urban Tree of the Year.  The SMA selects trees that are adaptable to a variety of harsh growing conditions with strong ornamental traits.  Their selections are being used as street trees in some towns and cities across the country.  The SMA's mission is to widen the knowledge base of arborists, designers and architects with the goal of adding diversity as well as beauty to the urban streetscape.

The 'Vanessa' cultivar has a number of qualities that make it desirable as a street tree: it is slow-growing, reaching a mature height of about 30'; it has an upright, almost columnar habit but has strong branch unions and is not prone to develop included bark (as some other columnar trees are); it handles reduction pruning fairly well, so its height can be managed by knowledgable municipal arborists if overhead wires are low; it has no major pests; it can tolerate both dry soils and seasonally wet ones.  PLUS it has spectacular fall color and beautiful flakey gray bark.  It flowers in late winter, before it leafs out - like witchhazel - but that can be an unexpected surprise for passers-by.

 Parrotia persica 'Vanessa' fall foliage


Parrotia flowers in late winterParrotia bark becomes more beautiful as it matures


I.C.Y.M.I. Biochar is the New Black

More from the NYS Arborist Meeting in January:

Mr. Hendrickson, the guru from Bartlett Tree Research, mentioned a magic ingedient in passing that I didn't know anything about - biochar.  It turns out that biochar has a rich history (no pun intended) as a soil amendment that "magically" makes plants and trees grow and that even helps soil structure and health.


Here are some facts:

Biochar is formed from organic material (otherwise know as garden waste) by pyrolysis: a thermochemical decomposition of organic material at high temperatures (390 - 570 degrees F) in the absence of oxygen.  It involves the simultaneous change of chemical composition and physical phase, and is irreversible. The word is coined from the Greek-derived elements pyro "fire" and lysis "separating".  In general, pyrolysis of organic substances produces gas and liquid products and leaves a solid residue richer in carbon content, char - aka biochar.  Pyrolysis differs from other high-temperature processes like combustion and hydrolysis in that it doesn't involve reactions with oxygen or water.

Biochar as a soil amendment has an ancient precedent - "terra preta", discovered in the 1950s by Dutch soil scientist Wim Sombroek in the Amazon rainforest.  It still covers 10 percent of the Amazon Basin.  As the nonprofit U.S. Biochar Initiative explains, “biochar has been created and used by humans in traditional agricultural practices in the Amazon Basin of South America for more than 2,500 years.  Dark, charcoal-rich soil (known as terra preta, or black earth) supported productive farms in areas that previously had poor and, in some places, toxic soils".  

Over the past 10 years, researchers have been investigating terra preta, now called biochar, as an agricultural resource. Typically when biomass decomposes or burns, virtually all of the carbon stored in the plant is released into the atmosphere as carbon dioxide, a greenhouse gas that contributes to global warming.  But when biochar is produced, roughly half of the plant’s carbon is retained as stable carbon in the biochar.  The other half is released as wood gases, which can be used as an energy source. This biochar cycle puts carbon from the atmosphere back into the earth, puts it to positive use in the soil and increases the amount of time it stays there.



Here's why biochar is "magic":

  • It provides a combination of moisture management and a way to store microbial food and plant fertilizer.  When there is an excess of water, food and fertilizer, biochar stores them.  When there is a deficiency, it slowly releases them back into the soil, where the plant or microbes can take advantage of them.
  •  It persists in the soil for years, greatly reducing(eliminating?) the need for re-application.  It is much more persistent in soil than any other form of organic matter that's applied to soil.  This is referred to as "stability" by the soil scientists.
  •  It is highly adsorbent.  It sops up humic acid, a food for soil microorganisms, and humic acid itself binds to fertilizers, keeping them from leaching out of the soil.


"What is special about biochar is that it is much more effective in retaining most nutrients and keeping them available to plants than other organic matter such as for example leaf litter, compost or manures. Interestingly, this is also true for phosphorus which is not at all retained by 'normal' soil organic matter". (Lehmann, 2007) 

from Cornell webpage; references as cited on that page

  • It is also highly adsorbent of water.  In conditions with greater than 60% relative humidity, it absorbs water.  And in conditions less than 40% relative humidity, it releases water.  So it is an enormous stabilizer of relative humidity in soil, which means less watering.
  • It is a way to "recycle" organic waste, and the off-gas can be used as fuel.
  • You only need a little, and it can be added as a soil amendment to existing planting beds, like tree wells.


But there are caveats as well:
  • The vast majority of research has been into biochar's effects on agricultural soils and crop yields.  Until very recently, there has been little research on biochar in urban and suburban soils, trees and shrubs.  Agricultural crop research goes a lot faster than urban tree growth research - that will take years.
  • All biochar is not created equal - it matters what organic matter was used to make it and whether it has been tested for contaminants and properly de-watered.
  • This is not a plug - but Bartlett uses biochar as part of their soil improvement and root invigoration treatments.  Bartlett Tree Research Laboratories is collaborating with the Morton Arboretum to look at the effects of adding biochar to existing tree wells in Chicago.
  • Mr. Hendrickson said that Bartlett has a supplier that they have vetted extensively.  


Here are some of the initial findings that Bartlett Tree Research Laboratories and the Morton Arboretum have publicized for biochar:


  • Biochar can have a measurable positive impact on both soil quality and plant growth.
  • Biochar works best in combination with compost.  Biochar itself doesn't provide nutrients, but compost does.  So when you mix them together, you're "charging up" the biochar with nutrients.  Their research also suggests that biochar improves the performance of compost - i.e. when the two are blended, trees and shrubs show better growth than with either of the two alone.
  • More is not necessarily better - in fact it can be deleterious.  (like anything!) Their research is trying to determine the optimal amount, but they already know that a little bit goes a long way.
  • Biochar may also promote disease resistance - this is only preliminary greenhouse-based research but will be looked at in future studies.

To find out more:

soils.org is an interesting website - this link will lead you to a story about the Morton Arboretum work on tree growth using biochar

And, of course, Cornell has a lot of expertise - this link will provide you with both information and lots of references




Sustainability in 2014



It's a word that everyone uses.  But what does it mean?  To me, for a long time it was the classic definition from the 1987 WECD conference - sustainable developments are those that "meet present needs without compromising the ability of future generations to meet their needs".  www.un-documents.net/wced-ocf.htm

In the Sustainable Sites Intiative, their mission statement started with "First, do no harm."

But at this year's NYS Arborists meeting, I heard a different perspective from one of the speakers, Neil Hendrickson of Bartlett Tree Research, who made me start to "think differently".

He said - "do no harm" is not good enough at this point - so much "harm" has already been done that now we need to be active - we need to sequester carbon, clean the air and water and manage the soil.  

Here are some of the points he made:

  • 2012 was the hottest year on record in the US
  • 2013 was the 4th warmest year in the world
  • Temperature rise is associated with increases in both the minimum and maxiumum temperatures - both of these affect plants
  • In 2012, 90% of the "record temps" were HIGH temperatures and the Plant Zone Heat Map shows more nights above 70 degrees F
  • We are seeing warmer winters and warmer autumns - and fewer frigid nights 
  • Spring is arriving earlier
  • There is a longer frost-free season
  • There's been a 74% increase in heavy downpours
  • Models say: expect more days above 95 degrees F in August


Climatologists predict that future climate shifts will include more frequent extreme heat and more frequent extreme cold, as well as more extreme hydrologic events like searing drought and flooding rains.  High pressure systems are tending to intensify because dark water replaces white ice as the polar ice melts.  Dark water absorbs more energy rather than reflecting it, and this energy evaporates more water into the atmosphere.  Increased energy in the atmosphere leads to an unstable jet stream and unpredictable variability.  Of course, the system is extremely complicated with tons of feedback loops and this is a gross over-simplification.  But certain climate changes are irreversible on a time scale of 1000 years, even if no more CO2 is put into the atmosphere - we need to be aware of some of the changes and their consequences.  And try to actively counteract them.


  • When we disrupt ecosystems, we decrease species diversity.  With less diversity there are fewer possibilities for adaptation - plants that can't adapt fast enough are likely to die off.
  • Increases in the frequency of heat waves and drought increases stress on plants, which increases their susceptibility to pests and diseases.
  • An increase in warm nights means that respiration goes up but photosythesis does not.
  • Longer frost-free seasons mean that plants may not go through acclimitization to extreme cold events and may not be cold tolerant.
  • Invasives can adapt more quickly (that's part of what makes them invasive) so they can out-compete natives.


Here are some of the effects of climate change on pests:


  • allow northward expansion of warm-weather insects
  • increase the number of generations per year in multi-generation insects
  • favor pests over predators
  • disrupt the timing between flowering and pollinators
  • beneficial insects might "miss" their pest host, allowing a pest population to increase
  • the polar vortex could kill the beneficial predator but not the invasive pest
  • invasion of new habitats by pests - because insects can adapt faster than trees
  • warmer winters and less snow can contribute to increased deer populations


His take home message : change is inevitable and unpredictable.  His suggestions about what we should be doing above and beyond "do no harm" are a practical and practiceable definition of sustainability for 2014:

1. Take care of the soil.

2.  Don't get hung up on native plants - that's looking backward and the environment is changing forward.

3.  Look for plants that are better-adapted if your aren't doing well.

4.  Increase diversity.

5.  Capture rainwater

6.  Preserve beneficial insects.


The next day, I attended a seminar at NYBG given by Jane Didona, a Landscape Architect, talking about LEED guidelines as they relate to Landscape Design.  She had another perspective on the definition of sustainability, one that looks at the overall site, including the buildings - She showed three overlapping circles - Social Equitability, Economic Feasibility and Environmental Soundness - Sustainability is the intersection of all three of these qualities.

 Ancient Native American Proverb:

Treat the Earth well.  It was not given to you by your parents, it was loaned to you by your children.  We do not inherit the Earth from our ancestors, we borrow it from our children.

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