Henry Homeyer: Let’s get the dirt, on dirt

By Henry Homeyer
©2019 Telegraph Publishing LLC

As we move from dreaming to planting, we all want to offer our plants the perfect soil. This leads some gardeners to buy a big bag of 10-10-10 and sprinkle it heavily on everything. For others, manure or compost is the answer to increasing soil productivity and plant health. And then there are bagged minerals, organic bagged fertilizers, rock powders and more.

There are many things that plants need. Scientists agree that plants need minerals for health: nitrogen (N) for promoting green growth; phosphorous (P) for better roots and promoting flowers, seeds and fruits; potassium (K) for strong cell walls to survive drought and cold. These three elements are often called “the big three” and listed as percentage by weight on fertilizer bags (5-10-5, for example). Chemical fertilizers have just those three elements, plus inert fillers (which would be 80% in the example cited).

 

Additionally, there are elements that are needed in smaller amounts including magnesium, calcium and sulfur. In very small amounts plants need iron, chlorine, manganese, zinc, copper, boron, molybdenum and nickel. None of those are found in chemical fertilizers, but are present in unlisted amounts in bagged organic fertilizers, and in good compost.

Bagged organic fertilizers are made from natural ingredients, things like ground oyster shells and seaweed, or dehydrated chicken manure, or cotton seed meal and peanut hulls. Added to the mix are minerals such as rock phosphate (a good source of slow-release phosphorus) and green sand (a source of potassium from the sea).

These are slow release fertilizers. Most of the ingredients are not water soluble, but are broken down and utilized in concert with bacteria and fungi in the soil. That is good, as they are not washed away in rainy times the way many chemical fertilizers are.

Here in the Northeast most soils are a bit acidic due to acid rain, so adding limestone is good for getting your soil near neutral. But not all plants need the same things in the soil. Blueberries, for example, need very acidic soil. Instead of lime, they may need sulfur to make the soil more acidic.

A simple soil pH test kit can be purchased for under $10, or you can send a sample to your state Extension Service for testing, Go online and search for soil tests in your state, and you will find how to collect the soil, and where to send it. A basic soil test will tell you much in addition to the soil pH.

I’ve been adding finely ground granite dust to my soil for 20 years or so, and a commercially prepared rock and mineral soil supplement called Azomite for nearly as long. I’ve done side-by-side trials of plants with rock powders and without them, and have seen dramatic differences. Soils with rock powders have helped plants survive drought, and have increased crop yield in my peppers.

The mechanism by which rock powders work is unknown. I interviewed a soil scientist who pointed out that every 10,000 years or so we’ve had glaciers come down and deposit ground rock, distributing obscure minerals in the soil. Maybe the rock powders I add are just mimicking what the glaciers have done – though not recently.

When it comes to compost, it is pure gold, from a soil perspective. It has all the minerals needed by plants and good compost also has literally millions of beneficial bacteria, fungi and other living things in each spoon of goodness.

Beneficial organisms in compost work with your plants, sharing minerals with your plants; they benefit from sugars exuded from the roots each night. That’s right, over eons the plants and microorganisms have developed a mutually beneficial system.

I should explain that compost is not high in nitrogen. But most vegetables and annual flowers don’t need a lot of nitrogen. Nitrogen will make veggies like peppers or tomatoes grow big plants, but often those big plants do not produce a lot of fruit. Most annual flowers do not need much nitrogen.

How much compost you should use can vary. I have been putting an inch or two over my vegetable beds every year, and working it in. If you are buying it by the bag, even half an inch is good – with some extra in the hole with each tomato.

For trees and shrubs, most do not need fertilizer or those tree fertilizer spikes sold at hardware stores. Mother Nature does not provide fertilizer, she adds organic matter to the soil over time as leaves decompose and living beings of all sorts die and add to the soil.

That said, if you live in a new subdivision, your soil may be nothing but sterile subsoil with a thin layer of “topsoil” spread by the contractor. Adding organic matter to the soil in the form of compost will help it become biologically active. It will add minuscule amounts of the less common minerals.

Mulch all your beds with ground leaves, grass clippings, mulch hay or straw. These will break down with time, and add organic matter to the soil. Breakdown of that mulch is done by bacteria and fungi.

Treat your soil to some compost at planting time. And if you use fertilizer, don’t overdo it – more is not better. Read the directions of anything you add to the soil.

Henry Homeyer is a long time UNH Master Gardener and the author of 4 gardening books. He can be reached at henry.homeyer@comcast.net.