The soil

by M. Arjoca, vegetalshapes.com

Soil in a bucketThe third important element is the earth because it's the food source for plants. So it's important to know what kind of soil is on your field. The soil is the upper layer of the Earth and is a mixture of minerals and organic materials (decayed plants and animals etc).

Generally it takes into account 3 aspects when you say “good soil” for gardening:

The soil texture refers to the presence in different proportions of sand, silt and clay. These materials have different sized granules which form the soil's structure. The granules of clay are so small and stay so closed together that the water, the air and the roots can just a little bit pass through. If you want to dig a clay field you’ll see that is almost impossible because the clay gets stuck on shovel.

The sand has the biggest granules and the size of silt granules are between the clay and the sand ones. The sand granules can’t stay too closed together and the water just pass through. The roots and the air can move freely. If you rub some sand between your fingers you feel that the granules are rough, but if you rub silt it feels like you have flour on fingers. The clay can be modeled if you mix it with some water.

There are many lab tests which can establish the soil texture, but if you want a simple method and is not important to have a precise result, you can proceed this way. Take a hand of garden soil and squeeze it. If it breaks and flows through your fingers this means it’s a sandy soil, but if it forms a ball this means it’s clay soil. If it forms a ball you can break it when you poke it then it's a silty soil.

Here it's another simple test. Take a sample of soil from garden and let it dry, then put it in a jar. Pour water over, shake it, turn the jar upside down few times and then put it in the normal position on a flat surface. After a minute mark the level of the particles on the bottom of the jar. This is the level of sand (sand is heavier). After few hours mark the level again. This is the silt level. After a day mark the clay level.

These simple tests give you an idea about the relative percentage of the three elements.

A good soil for garden has not too much clay or sand but about 40% sand, 40% silt and 20% clay. It’s a loose, rich in humus soil, retains the nutritional substances, lets the water surplus drain and can be easy worked.

If the soil is not so good there are many methods of improving it. Adding compost is one of them.

The soil fertility refers to it’s capacity to give the nutritional substances that plants need. Generally the plants use most nitrogen, phosphorus and potassium, but they also take from soil other substances like: calcium, iron, magnesium, zinc, sulfur etc. The fertile soil is rich in nutritional substances and has a good drainage of water.

Most nutritional substances are on the surface of earth, where the soil is darker, and they lower to deeper levels. The decayed leaves, stalks, plants, animals and animal feces make the soil fertile.

Nevertheless the excess of any of these substances causes burns on plants.

There are tests which establish the level of the three elements in soil. If the soil is not too fertile you can add organic fertilizers and compost.

The soil pH is a measure of the soil acidity or alkalinity and varies on a scale from 0 to 14. The acidity is between 0 and 7 and the alkalinity is between 7 and 14. So the neutral level is 7.

soil pH

0
7
14
     
Acid
Neutral
Alkaline

The pH of acid soils is situated between 0 and 7, and the pH of alkaline soil is between 7 and 14.

The pH is important for gardening because many plants prefer either an acid soil or an alkaline soil and some diseases proliferate when the soil is acid or alkaline. Also the absorption of some substances from soil depends on pH.

Most vegetables prefer neutral-slightly acid soils, but there are plants which prefer a certain type of pH. For example the strawberries and the potatoes prefer an acid soil, but the cabbage and the cauliflower prefer an alkaline soil. Generally the plants resist in soils with pH closed to the one they prefer.

When the soil is acid (pH is below 6) the nitrogen, phosphorus and the potassium can be absorbed more difficult. When the soil is very alkaline (pH is above 7.5) the absorption of phosphorus, iron and magnesium is more difficult to be done.

In the case when the soil is very acid or very alkaline, the plants can not absorb in a proper way the nutritional substances they need and this can cause nutrient deficiencies (the plants turn yellow or just don’t grow).

If the plants are healthy, they grow and develop as it should be this means it's probably nothing wrong with your soil pH. If the plants don’t grow and have an unhealthy aspect then it may be a problem. There are many commercial tests which you can use to find the soil pH of your garden.

The areas with many rains or covered by woods have acid soil and the desert and arid areas have alkaline soil. Generally the areas with moderate rains and the plains have neutral soil.

What can you do when your garden soil is too acid or too alkaline?

If it’s too acid you can add limestone and if it’s too alkaline you can add coniferous leaves, sawdust, sulfur, dead leaves and other acid materials. Adding compost neutralizes also too acid or too alkaline soils.

Most plants prefer a certain type of pH (neutral-slightly acid), but they can tolerate soils with pH closed to that.

Here is a list with some plants and their preferences.

Name

         pH

Alfalfa

6.2-7.8

Apple

5.0-6.5

Apricot

6.0-7.0

Asparagus

6.0-8.0

Beans

6.0-7.5

Beets

6.0-7.0

Broccoli

6.0-7.5

Brussels sprout

6.0-7.5

Cabbage

6.0-7.5

Calendula

5.5-7.0

Carrots

5.5-7.5

Cauliflower

6.0-7.0

Celery

5.5-6.5

Chrysanthemum

6.0-8.0

Corn

5.5-7.5

Cosmos

6.5-7.0

Cucumber

5.5-7.5

Dahlia

6.5-7.0

Eggplant

5.5-6.0

Foxglove

6.5-7.0

Garlic

5.5-7.5

Horseradish

6.0-7.0

Leek

6.0-8.0

Lettuce

6.0-7.0

Melons

6.0-6.8

Nasturtium

6.0-7.5

Onion

6.0-7.0

Parsnip

5.5-7.0

Pea

6.0-7.5

Peanuts

5.0-6.5

Pelargonium

6.0-8.0

Peppers

5.5-7.0

Petunia

6.5-7.0

Potatoes

4.5-6.5

Pumpkins, squashes

5.5-7.5

Radishes

6.0-7.0

Rhubarb

6.0-6.8

Rose

5.5-7.0

Sage

6.0-7.0

Snapdragon

6.0-7.5

Soy

5.5-6.5

Spinach

6.0-7.5

Strawberries

5.0-6.5

Tagetes

6.0-7.5

Tomatoes

6.0-6.8

Turnip

6.0-7.5

Watermelon

6.0-6.8

Zinnia

5.5-7.5