Sunday, June 17, 2012

It's All About the Soil

Dirt...What is it?  Well, it doesn't come out of our kids clothes very easily, it rides on their cleats until it enters the house and lets go on the bathroom floor or in front of the couch, and it will accumulate under their fingernails until properly scrubbed away.

Soil, as we gardeners call it, is composed of minerals and organic matter.  The minerals are the indigenous rock that has broken down over time into small particles, and the size and mixture of the particles determines the type of soil.  Sand is typically the largest particle in soil and leads to a sandy soil that is loose.  Clay is the finest mineral particle and it tends to bind together into a very compact and heavy soil.  Silt is in between in both its size and binding ability.

The other components in a spade-full of soil are air and water.  When you combine the mineral types, organic matter, air and water you can have thousands of different types of soil.  On the left is a triangle that helps to determine the type of soil based upon the mineral components.  Red clay soils in the South are heavy because the particles are compact and they hold onto water and nutrients, hence they do not drain very well.  A childhood friend of mine owns a nursery outside of Charlotteville, VA, and his soil is a combination of red clay that provides an excellent balance for growing.  Many of our trees and shrubs in New England come from nurseries like this in the south.   Soils close to the ocean on Cape Cod tend to be very sandy and loose, and they do not hold onto water or nutrients.  The result is a plant palette of grasses and smaller shrubs that can exist in less fertile conditions unless you have good soil brought onto your property.

The 'ideal' soil has a mixture of particle sizes so that it can hold onto water, organic matter and nutrients, while not holding onto too much water and keeping air out of the root zone.  Balance, it works for humans too.

Plants won't just grow in minerals, they need other food and nutrients, and these come from the organic matter in the soil as well as the other natural elements that are in the minerals, air, water.

Why do we need this information? Along with sun and water, good soil is critical to the success of  plants in your garden.  If your plants are getting the right amount of sun, proper moisture and are failing to thrive, then the soil is the culprit.

This next part is going to get technical, but is important to understand how to best take care of your plants.  For Example:

If you fertilize your lawn but don't know the pH, you could be throwing hundreds of $s away every year.  If the pH is not right in the soil, the grass is not able to take up the nutrients supplied in the fertilizer.

If you fertilize your plant beds without knowing the pH, CEC or % of organic matter, you are also wasting money since the nutrient may not stay in the soil or be available to the plants.

The results of a simple test will help you determine the best course of action with regard to your plants and lawn.

How do we know what type of soil we have in our garden and whether we have enough organic material?  Test your soil at UMass.  I do this with most clients, and especially in beds where plants are not thriving and flowering.  For $15 (basic test + organic matter content) you can get a tremendous amount of information that will allow you to solve most any problem.  Three or four tests can cover an average property.  On a Brookline property I manages we did upwards of 30 tests one year.  When filling out the application, it is critical to let them know what the soil is being used for if you want to get the proper advice.  Complete instructions are on the site for how to gather and prepare the sample.  It is very simple and can be a fun project.  It is best to do in the off-season since they can get very busy.

So what will the results tell you?  I will only geek out on you a little, and it will take you back to high school chemistry.  For a couple of you who know far more than I do with regard to chemistry, I apologize in advance.

pH - It literally means potential Hydrogen.  A high pH (>7.5) means an alkaline soil and is good for certain plants like Lillac, Daphne, Spirea, Boxwood and many others.  Your lawn likes a slightly alkaline soil, which explains why you often need to add lime (Calcium) to your lawn with some regularity in New England. A low pH (<6.5) is an acid soil, typical in New England, which explains why we are often fighting with our lawns to keep them happy.  Plants typical to the New England garden love a slightly acid soil:  Rhododendron, Azalea, Dogwood (Cornus), Magnolia, Holly (Ilex), Coniferous Evergreens (Pine, Spruce, Fir, Chamaecyparis, etc.) and many others.  Mostly, a pH between 6.5 and 7.5 is fine.  However a bed full of Rhodendrons, Mountain Laurels, Azaleas would definitely do better with a pH in the 5s.  pH can be manipulated easiest with two basic elements.  Sulphur will make the soil more acid, while Lime (Calcium) will make it more alkaline.  Unfortunately, it is not always that easy.

% Organic Matter - This literally is a measurement of the organic matter in the soil.  It is important when collecting your soil to dig down 4+ inches so you don't include a bunch of compost or mulch that may be on the surface.  This is a measurement of organic matter that is available in the root zone for plants to utilize.

CEC - Cation Exchange Capacity - Very simply tells you the ability of your soil to retain nutrients.  Click the link for some crazy science if you like.  Sandy soils with low organic matter will hold few nutrients, while heavy clay soils have a high capacity.  This has to do with positively charged ions being held in the soil by the negatively charged clay particles.  This means that if you have a low CEC, adding fertilizer, lime or sulphur will do very little since the soil can not hold it.  The best way to improve a low CEC is to add organic matter, but the basic ability of soil to hold nutrients is determined by the amount of sand vs clay.  More silt and clay leads to a higher CEC.

Nitrogen - Is one of the big three macronutrients.  It is responsible for enabling the process of making Chlorophyll which makes the plants green and grow quickly.  Careful if you do add nitrogen, since improper application can burn the plants.

Phosphorus - Is responsible for flowering, fruiting and root growth.  Triple Super Phosphate is a quick remedy to plants that seem to be lagging in the flowering department, but if the pH is wrong for the plant, the nutrient will do nothing.

Potassium - Is responsible for plant metabolism and general vigor.  Just like with humans, a banana a day will keep an active body working well.

Calcium and Magnesium are also critical nutrients that being positively charged take up much of the Cation capacity.

Manganese, Copper, Zinc, Iron, Sulphur, Molybdenum, Nickel, Sodium and Boron are all micronutrients that rarely are a major problem, but each have a unique signature if they are deficient in the soil.

So What?

 A simple soil test will help you to learn about your garden beds and how to efficiently make them the best environment for your plants.  I suggest you perform several tests from several different beds.  Beds against the house may be quite different from those away in the back yard.  Always test vegetable gardens for the main purpose of determining the lead content.  Lead is easily taken up in vegetables and herbs.  Old houses or around old foundations can be quite dangerous.

I have used products from Espoma for years and trust in there organic practices and products.  Click the previous link and learn more about 'plant feeding basics'  and 'garden projects'.

Don't curse anymore over your plants not performing.  Learn why they are not doing well and help them do better.

Next week will be something a little lighter...some perennial flower eye candy.

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