Mad (Soil) Science
Getting the Low Down on Dirt….
The truth is you don't have to be a biologist, a geologist, or a chemist to be a good gardener but you should pay some attention to a few things early on to assure all your hard work turns into a good harvest later.
One of the simplest things you can do is test the pH of your soil. For just a couple of dollars, you can buy a test kit at most garden centers and in a very few minutes you'll know if your soil is acidic or alkaline.
[image error]I picked up two versions of one manufacturer's pH test. In my photo, the vial in the center and the hangcard on the right are a one-time pH test kit. The container on the left comes from a kit that includes enough material to run the pH test ten times. Both were inexpensive and this is not the only brand out there. I bought this because my favorite garden center had these on display when I was looking to buy. The kits are similar to the chemical tests you might use for pools and spas.
It's so easy. Take a soil sample, mix it with a little distilled water and an additive the kit provides, shake until the additive is completely dissolved, and leave it to "develop" for five or ten minutes.
[image error]I tested two samples: the soil in my vegetable bed and my finished compost. I'm not sure if my photo shows the results well but the soil had a pH of 6.0 and the compost was 6.5. Why test my compost separately? Vanity. I'm new to composting and I'm excessively proud of my efforts. I wanted to prove to myself that my compost was relatively neutral – as it should be. Well-composted materials will always be close to a 7.0 neutral reading and will help the soil approach the same. For that reason, I wanted to test my pre-amended soil to make sure it was also within an acceptable range.
Most vegetables do just fine between 6.0 and 7.0. A notable exception is potatoes. They like the soil a little more acidic and, though they will grow in soil with a higher pH, they will be more susceptible to certain diseases like scab.
Why is pH important? Having properly balanced soil allows the plant to absorb the nutrients it needs. I was reading about how this happens on a molecular level and, honestly, it is so complex that my head hurts.
I'm lucky that I can rest on my laurels and do nothing about my pH but what about you? It totally depends on the results you get. This is when knowing the staff at your local garden center pays off. The pH reading you get is probably typical of your region and they will help you pick a soil amendment to correct your specific problem.
Next comes Geology. Soil ideal for plant growth has mineral matter, organic matter, water and air. The mineral content is divided into three categories – sand, silt, and clay – identified by the size of the mineral particles.
On our property, we have a lot of clay: the soil particles are very, very small – microscopic, in fact. Sandy soil has much larger particles, visible to the naked eye. Silt is somewhere in between. Another term you will hear is "loam," a combination of the three. The type of soil you have will give you information about its texture and (my topic for today) is predictive of drainage.
You can test your soil drainage very easily: dig a hole about a foot deep and a foot wide and fill with water. After it has drained away, fill the hole again. Time how quickly it drains. It should take three or four hours. Faster than that, you could have a lot of sand and will have to amend with something to help hold the moisture. Slower, you may have clay and you need to incorporate amendments to allow water to pass through more quickly.
[image error]How bad is my clay soil? I picked a spot I knew was most undisturbed clay. The second filling was only half gone after twelve hours. For several years now, we have been mulching the soil in our backyard with wood chips. The obvious reason is to keep down the weeds but as the chips decompose, they add organic matter to the soil, improving its structure. When we put in a cactus and succulent garden a few months ago, to make sure those plants had more favorable conditions, we created a raised bed and added lots and lots of sand to improve drainage. I've included a photo to show how granulated the amended soil is.
Why is drainage important? "Vegetables don't like to stand in water." That's what people will say about plants that are sensitive to slow drainage. In reality, waterlogged soils have no room for air – the plants are drowning. Alternatively, if your soil drains too quickly, plants won't have a chance to absorb enough water and nutrients. Either example of poor drainage can also increase susceptibility to disease.
[image error]While you have that cubic foot of soil dug out, you can do another little test: check your earthworm population. In a cubic foot of soil, you should have 15 or 20 worms (even counting little babies). Earthworms will help your soil structure and will increase the available nutrients. Even as they are adding castings to the soil, their little tunnels help drainage. Earthworms cause no damage to a growing plant – they only consume decaying organic material. If you have just a few worms, the population will grow if you have a healthy, active garden.
The last bit of science I want to talk about relates to seeds I'm starting indoors. Because we are experiencing a La Nina weather pattern this winter, summer will come early but I still don't have confidence that nighttime lows won't cause damage. Also, starting them indoors allows me to lavish attention on the seedlings and protect them from pests. When starting seeds, some people use garden soil and/or compost but I prefer a seed starting mix. There are several brands and I don't have a preference except I am looking for a sterile, soilless mix.
Soilless? This is when the biology comes in. There are living things in the soil. Totally necessary to healthy plant life are good fungi, bacteria and nematodes. But then there are the bad fungi, bacteria, nematodes, plus viruses, protozoa, and more – these are called pathogens. There are pathogens in all soils. But a seedling that has been given a chance to grow and develop a little before set out into the garden is stronger and more resistant to disease.
I can't tell you how many times I've lost a seedling to "damping off," a deadly infection by a fungus. Now this is interesting because before I figured out the clay soil issue, poor drainage provided the ideal conditions for fungi to infect my young plants. These are not all separate topics but factors that interact closely in a garden.
As I am starting this year's vegetable garden, these were the things that I found myself thinking about that came from book learning and from more experienced gardeners.
Laurie Gore is the Deputy Heirloom Gardener for Zone 9. She has taken a pH Test and is neutral. She and her husband Frank live in Bonita, California.
