The Second Principle of Xeriscaping - Soil Amendment




And then the bears ate her.

 

As discussed last week, the second step of creating a low-water garden is to address your soil, possibly adding components that will decrease water usage.  Depending on the quality of your soil, or the type of plants you are incorporating into the landscape, soil amendment may not be necessary.  Check the soil.  Ideally, farmers desired a soil profile called 'Loam'.  Loam falls into the Goldilocks Zone of soil particle size.  It is not too sandy, it is not clay.  Loam is just right.  If you are lucky enough to possess loamy soil, then congratulations!  You can go home early and skip this lecture.

Alternatively, you may decide to use plants that are best suited for the soil profile you have.  (This is part of the 4th principle, and will be addressed later.)  If this is the case, then amendments aren't as crucial.  If you have zoned your garden, consider amending the soil to the zone's water requirements.  The low-water zones won't need nearly as much as the oasis zones. 

The goal of amending soil is to make gardening a more sustainable process.  With that in mind, I shall look at a different strategies, and discuss the pros and cons of each.  Not every amendment is truly sustainable, and it is possible that a balance will have to be reached - one between adding to the ground, and preventing water loss.

Inorganic Amendments

Amending the soil through inorganic amendments is basically just changing the soil profile.  This may take a great volume of material, making it a somewhat impractible, and not the most sustainable practice. The materials have to come from somewhere, so by adding them to your ground, you are merely taking the ground from a different location.  Consider also the carbon footprint created from transportation.

Disregarding fertilizer for the moment, these type of amendments rarely offer any nutrient value.  The main reason to add inorganic material is to improve drainage of the existing soil, and gain a better overall texture.  This can be obtained with Sand, Perlite or Vermiculite.  Large quantities of all are needed to effect a change.  Perlite and Vermiculite are quite expensive, and are only short term solutions in the outdoor environment.  Their best use is in a greenhouse environment.

Hydrogels are a relatively new product for soil amendment.  They are polymers designed to increase the water capacity of the soil.  However, the long term consequences of this addition are unknown, and the effect only lasts a few years before the hydrogels are broken down.  Also, addition of hydrogels won't decrease water requirements, only frequency of irrigation.

Fertilizer can be classified as a soil amendment; you do add it to the ground.  Fertilizer adds macro and micro nutrients alike for the plants to take up.  They tend to be water soluble, which means that the plant can absorb them quickly, but also means that they can be washed away.  Unless slow release fertilizers are used, the plant's growth response may be rapid initially, and then slow when the food runs out.  This can be dangerous is some plants; hasty, stretching growth may leave it weak and vulnerable in critical aras.  Fertilizers need to be added at least once a season (depending on the type), and may increase the salinity of the soil.

Organic Amendments



A Carbon-based Life Form



Organic has become a buzzword over the past two decades.  Agriculture and horticulture has embraced the term to an extent.  So has the film industry, though that is neither here nor there.  Chemically speaking, organic refers to anything with carbon in it.  Biologically, this planet has produced carbon-based lifeforms.  In terms of soil amendments, organic means that it was once alive, but is now dead, and broken down.

Specifically, organic matter is in the process of breaking down, and eventually, its effect will be lost, requiring continuous applications.  Still, organic matter comes from natural sources, so it hasn't lost the sustainable hat just yet.

"Cats have Pos"
 Cations are positive ions

The benefits using organic matter for soil amendments include the nutrients they contain, the aggregate-forming properties that improves the workablity of soil.  Organic material can improve the Cation Exchage Capacity, or the ability of soil to attract and store nutrients.  Adding organic matter may also improve the soil's water capacity.  However, that is not confirmed at this point in time.

A compost pile is an excellent source of organic matter, and is inexpensive, as material can come from your home and garden.  This is also a good way to reduce waste.  The important thing to remember when composting is the proper construction of of the pile.  The breakdown of the organic material is done by organisms, and they require certain conditions to survive. 

Be careful not to put diseased plants in the compost pile, as the disease might be able to survive, and then be spread around your garden.

Manure is one of the traditional organic amendments; however, these days, it is not produced in traditional methods, and this has lessened its value.  Fresh manure can burn a landscape, it should be composted or aged before applying it.  As a nutrient source, manure is better than an equal quantitiy of fertilizer, however, the quality of the product depends on many factors, such as the age, the type of animal, and the animal's food source.



Caution: May Contain Pixies
or Bowser
(Photo by Michael Maggs)



Peat Moss will improve the soil structure, however, it is acidic in nature.  It is useful for plants that thrive in acidic environments, though it can be expensive.  Topsoil can be added to the garden, though not all topsoil is equal, and harvesting topsoil is not sustainable.  There is also the possilbility of herbicide contamination, which should be tested for.

Mushroom compost is the material used to grow mushrooms in.  Adding mushroom compost in the fall, before winterizing the garden will help improve the soil's structure, though the mushrooms will have already taken up most of the nutrients. 

Cultural Practices

Simply tilling the soil can have an effect.  Tilling improves aeration and loosens the soil, allowing roots to spread through the soil more easily.  Be careful not to overwork the soil, however, as this will break down aggregates.  The frequency of tilling may also hasten the break down of organic material, necessitating further amendments.

What Does it all Mean?

By properly amending the soil, it is possible to improve the way water moves through it, hopefully decreasing the amount of water you need to maintain your garden.  It is also possible to improve the health of your plants, and healthy plants are better able to survive whatever conditions nature throws at them.