Soil and Soil Types – The Foundation of a Vegetable Garden

soil types

Soil Types

soil typesIn gardening, soils are generally considered in three types: sand, silt and clay.  These types refer to the size of the majority of the mineral elements making up the soil. Sand is the largest and clay, microscopic, is the smallest.

Soils are generally defined based on their composition of these three ingredients (sand, silt, and clay.) Sandy soil is mostly sand. Clay soils are mostly clay. However, the best soil for farming and cultivating around the world is known as loam, which is a relatively even composition of all three soil types. Specifically, optimal loam is defined as approximately 40% sand, 40% silt, and 20% clay. It is this, loam, which comprises the most fertile growing areas around the world.

If you are asking yourself now “Which soil type do I have?”, there are some simple ways to know the answer. Sand is easy to tell: it’s coarse and light (think beach). Silt, with a particle size between clay and sand, floats in water as a suspension, and when it’s dry, it turns to dust. Clay, in its wet form, is a workable mud or slip, and when it’s dry it turns hard as adobe.

Loamy soils have good body and generally good moisture retention and drainage capacity.  Both are extremely important. The number one cause of plant failure in a vegetable garden is bad water management. Either the plant dries out, causing the tiny hair-like root extensions to die, or these hair-like feeder roots are literally drowned by soil which fails to drain properly. In either case, this causes major stress to the plant. A soil which allows a plant to remain moist rather than dry or wet produces optimal growth.

Soil is the foundation of a healthy garden, and the healthy microorganisms in soil actually aid the plants in obtaining their nutrients, healthy soil is essential to a vegetable gardener.  Chemical fertilizers may yield quick and visually impressive results in the short term, but long term they not only destroy the health of the soil, they also deliver only visually appealing food with no nutritive value to speak of in comparison to vegetables grown in healthy soil.

It is a pretty good rule of thumb that no matter which of the soil types you have when you start a garden, there is lots of room for improvement, and improvement is not difficult to accomplish. It is also true that the longer you garden in one place and really take care of the soil, the healthier the soil, and thus the garden will become.

Vegetable gardens do best in loose loamy soil with lots of organic matter and a slightly acidic pH. Most locations are not blessed with ready-made vegetable garden soil, so you’ll need to do a little investigating of the soil you have and build according to what you find.

Get a Soil Test to Determine What Your Soil Needs

You will want an accurate soil test to determine the pH and nutrient levels of the soil so that you can make amendments as needed to provide the plants with all they need to thrive.

Many new gardeners skip this step to their great detriment. Don’t skip it! It will give you the essential information you need to succeed in vegetable gardening and without it you are just throwing seeds, plants and your time and effort into the wind.

What to Test

A simple pH and NPK soil test kit will do the job of informing you of the acidity of your soil as well as the levels of Nitrogen, Phosphorus, and Potassium. The test result will help you to determine if you have to add any of these three major nutrients to your soil.

Preparing a Soil Sample for Testing

To collect soil samples for testing, use a clean spade or trowel and take slices from the garden area down to six inches in depth. Note: There are two ways to approach the testing. Either test all of the soil in one test for overall results, or test different locations around the garden individually. So decide which way you want to test and then either mix the samples or not, based on your choice.

Place the sample(s) in a dry clean plastic, glass or ceramic container (a bucket or recycled plastic container or even a cereal bowl will work fine.) Let the samples dry thoroughly for 24 hours before testing.

Avoid taking samples where amendments have been added, such as fertilizers or manures as these will skew the results and fail to provide a true reading of the soil condition.

Where to Get Your Soil Test

Most county and/or university extension offices provide a simple soil test kit and charge a very modest fee for the test. Otherwise you can purchase a simple soil test kit at the local hardware, garden supply store or online.

The pH Factor

The pH test is measuring the acidity or alkalinity of the soil. This measure is based on a scale of 1 to 14. A pH of 7.0 is neutral. Any values below 7.0 are acidic, and any values above 7.0 are alkaline.

The ideal pH range for growing vegetables is 5.8 to 6.5, which is a slightly acidic soil. PH ranges below 5.8 will tend to be too acidic, and anything over 7.5 will be too alkaline. Once you’ve determined the pH values of your soil, there are several ways to either increase or reduce the acidity of the soil.

Lowering or Increasing Acidity in the Garden

Tip:  The introduction of peat moss or elemental sulfur can be used to increase acidity in the soil.

For most gardeners a 2 inch layer of peat moss over the garden surface and worked in to a depth of 6 to 8 inches will provide enough increase in acidity to reach the slightly acidic levels vegetables require.

For those needing additional acidity, the application of elemental sulfur is the first choice for quick and plant-safe action. Read the Oregon University Soil Acidification Guide for more information.

Tip: Increase alkalinity with wood ash or lime stone.

To increase soil alkalinity in overly acidic soils, additions of limestone (finely ground or granules) or wood ash may be used.

These additions to increase acidity or alkalinity must be made based on the results of your soil testing. If you are new to these practices, talk to a local nursery or university or county extension office to get advice on local materials available and best practices in your area.

Rototilling: Quick Fix Nutrient Release or Soil Destroyer?

While many modern vegetable gardeners start each season by dragging out the rototiller and churning up the whole garden, this is actually damaging to the soil and while it may provide a good crop the first year, as the nutrients are released, it also destroys the structure of the soil and disrupts the many living organisms which make up healthy soil.

One disadvantage of rototilling is that each successive year it is less effective at giving that ‘nutrient boost’ as the microorganisms cannot replenish and re-develop quickly enough to keep up with the soil depletion by the garden and tilling method without significant amendments.

Raised Beds: No-Till Soil Building

More recently as the popularity of raised-bed gardening has taken hold, the benefits of minimal digging to create the raised bed and then applying generous amounts of organic matter and never walking on the beds themselves has demonstrated to many gardeners the power of truly healthy and living soil.

Unlike rototilling, a raised bed will tend to become more productive and healthy over time, as the micro-organisms are left undisturbed and can continue to multiply and work the garden soil for you, year after year.

Permaculture: Sheet / Straw Mulching

Permaculture has introduced yet another and even less strenuous, less invasive and simpler method of soil preparation for a garden by simply using sheet or straw mulching. In this method, which varies only by how the mulching is laid down, the ground is left undisturbed, except for taking a garden fork and piercing it at regular intervals to open it up and allow air and water in.  The plot is mowed or cut short and all the matter cut is left in place, weeds and all.  Next, depending on the method you choose you either lay down manure and compost and then straw or start with manure and a thick layer of newspaper or cardboard, then add a layer of manure and then the compost and then top with the straw, leaves or whatever is available that is seed free and can act as a thick mulch.  The top mulch layer should be at least 8 inches thick and do not be afraid to go higher.

Straw or sheet mulched beds can be set up in fall and left over winter or set up just prior to planting. The longer they have to set up and build the more productive the first year’s garden will be; however, a good garden can be had in the first year with use of compost and amendments as needed to balance pH and mineral needs. You should still do a soil test prior to laying down the mulches to get an idea of the soil underneath, as the garden will grow down into that soil from above.

Learn more about amendments and soil improvement for increased yields and healthier gardens.


Further Discussion of Soil Types:

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