In the Garden – September


Soil is something that crop farmers think about naturally, yet baffles some gardeners. The baffling aspect has to do with the complexity of soil, which is truly amazing.

Healthy soil is richly complex, a matrix of materials that support teeming micro- and macro-organisms. Hydroponic gardening bypasses soil, and container gardening generally uses commercial potting medium. But we dirt gardeners need to understand our soil in order to grow plants successfully.

The first key is soil texture – the coarseness of the soil as determined by the size of the inorganic rock particles in it.

A coarse soil will admit lots of air and water. But it won’t retain the water, which drains too fast, taking a lot of necessary nutriments along with it. Many plants will die from dehydration and malnutrition.

A dense, finely-grained soil won’t let in air or release water, letting a plant suffocate or drown. We call coarsely-textured soils sandy and finely textured ones clay. The ideal midpoint of medium texture is called loam or silt. Any walk along a sandy beach will convince you that some plants do not need an ideal soil texture to grow. But are those the plants you want to grow at home?

Unfortunately, the dominant surface soil in Point Roberts is on the sandy end of the continuum, although there are areas of loam and clay. If you have had a septic system installed in the last 30 years, its application will contain a ‘soil log’ that records the texture of your soil.

If you can’t find your old soil log, it’s easy to do your own test. As a matter of fact, it’s a great project for children because it involves making mud pies. Dig a generous handful of soil. Remove visible stones and organic matter. Squeeze the soil into a ball with your bare hand.

If the ball is crumbly, keep splashing on water and squeezing until you can form a ball of soil that doesn’t fall apart. Then rub the surface of the ball. If it is quite gritty, you have sandy soil. If it is very smooth but sticks to your fingers, you have clay soil, with smooth, non-sticky loam falling between these two extremes.

To get a finer picture, roll the ball into a vertical column and use the pressure of your thumb to start shaping a ribbon that squeezes up out of your grip. If the ribbon reaches more than two inches before it breaks into pieces, you have too much clay for most garden plants. If you get a ribbon of one-to-two inches, your soil is loamy. Sandy soil won’t form a good ribbon before it breaks off.

I know from my soil log and this test that my top soil is loamy sand that drains quickly. That might be great in winter but less than ideal in summer, unless I confine myself to alpine and succulent plants, or do a lot of irrigation. In all likelihood, you are dealing with the same challenge.

The easiest way to amend both clay and sandy soil is to add generous amounts of compost or truck in a load of commercial garden soil. The latter is generally a mix of composted bark mulch and sand. Compost does not amend the basic solid texture of your soil. However, the organic material in compost will retain water in sandy soil and provide much-needed aeration and drainage in clay – sort of a magic cure for a less-than-ideal texture.

If you have previously incorporated compost or commercial mix into your garden, don’t assume that amending once does the trick. Compost breaks down at a fast rate in sandy soil. If it’s been more than a couple of years since you amended your soil, it’s time for another test. 

This time, consider a test that will show how much organic matter is left in your soil. Unfortunately, accurate home testing is difficult and laboratory testing is expensive. So let’s go for the guesstimates. When the soil is cool and moist, dig a six-inch hole and check to see if there is a healthy population of earthworms and other critters busy down there feeding on that compost. An organically-rich soil will also smell like soil, and not like rocks or raw compost.

Now take a handful of soil, remove visible stones and organic matter, put it in a mason jar with water, shake and then walk away. Overnight, the solids will settle, and the band of material floating on top is organic. If the band of organic matter is barely a skim and the water in the middle is paler than a rich brown, you need to add more compost. This is far from a foolproof test, but it sure is easy and cheap.


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