COLORADO SOIL
How To Identify + Amend Various Soil Types
For Healthy Vegetable + Plant Growth
If you’re planning to get serious about gardening it’s crucial you get to know your soil type. No matter how much work you do in your yard and garden, all that careful sowing, weeding and tending could be in vain if the quality of your soil is not up to scratch.
Soil provides your plants with the vital nutrients, water and air that they require for healthy growth and development. But each plot of ground has its own blend of minerals, organic and inorganic matter which largely determines what crops, shrubs or trees can be grown successfully.
Ideal soil conditions for specific crops can be created in contained plots such as raised beds or planters, but for larger gardens and landscapes it helps to understand the characteristics of the soil you have to work with.
The Six Types of Soil
There are six main soil groups: clay, sandy, silty, peaty, chalky and loamy. They each have different properties and it is important to know these to make the best choices and get the most from your garden.
1. Clay Soil
Colorado has a lot of clay. Clay soil feels lumpy and is sticky when wet and rock hard when dry. Clay soil is poor at draining and has few air spaces. The soil will warm up slowly in spring and it is heavy to cultivate. If the drainage for the soil is enhanced, then plants will develop and grow well as clay soil can be rich in nutrients.
Great for: Perennials and shrubs such as Aster, Bergamot, or Flowering quince. Early vegetable crops and soft berry crops can be difficult to grow in clay soil because of its cool, compact nature. Summer crop vegetables, however, can be high yielding vigorous plants. Fruit trees, ornamental trees and shrubs thrive on clay soils.
If necessary, amend with a mix of materials that can aerate and break up the clay, creating a lighter structure, depending on the size of the area:
• A small amount of Pea Gravel or Sand if necessary (with other materials) to aerate and assist water flow
• Compost, or Soil Pep (Light Flaky Mulch with clay-busting action)
• Planting Mix or Lighter Soil from another area
3. Silty Soil
Silty soil feels soft and soapy, it holds moisture, is usually very rich in nutrients. The soil is easily cultivated and can be compacted with little effort. This is a great soil for your garden if drainage is provided and managed. Mixing in composted organic matter is usually needed to improve drainage and structure while adding nutrients.
Great for: Shrubs, climbers, grasses and perennials such as Mahonia, New Zealand flax. Moisture-loving trees such as Willow, Birch, Dogwood and Cypress do well in silty soils. Most vegetable and fruit crops thrive in silty soils which have adequate adequate drainage.
5. Chalky Soil
Chalky soil is larger grained and generally stonier compared to other soils. It is free draining and usually overlays chalk or limestone bedrock. The soil is alkaline in nature which sometimes leads to stunted growth and yellowish leaves – this can be resolved by using appropriate fertilizers and balancing the pH. Adding humus is recommended to improve water retention and workability.
Great for: Trees, bulbs and shrubs such as Lilac, Weigela, Madonna lilies, Pinks, Mock Oranges. Vegetables such as spinach, beets, sweet corn, and cabbage do well in chalky soils.
2. Sandy Soil
Sandy soil feels gritty. It drains easily, dries out fast and is easy to cultivate. Sandy soil warms up fast in spring and tends to hold fewer nutrients as these are often washed away during wetter spells. Sandy soil requires organic amendments such as glacial rock dust, greensand, kelp meal, or other organic fertilizer blends. It also benefits from mulching to help retain moisture.
Great for: Shrubs and bulbs such as Tulips, Tree mallow, Sun roses, Hibiscus. Vegetable root crops like carrots, parsnips and potatoes favour sandy soils. Lettuce, strawberries, peppers, corn, squash, zucchini, collard greens and tomatoes are grown commercially in sandy soils.
4. Peaty Soil
Peaty soil is a darker soil and feels damp and spongy due to its higher levels of peat. It is an acidic soil which slows down decomposition and leads to the soil having fewer nutrients. The soil heats up quickly during spring and can retain a lot of water which usually requires drainage. Drainage channels may need to be dug for soils with high peat content. Peat soil is great for growth when blended with rich organic matter, compost and lime to reduce the acidity. You can also use soil amendments such as glacial rock dust to raise pH in acidic soils.
Great for: Shrubs such as Heather, Lantern Trees, Witch Hazel, Camellia, Rhododendron. Vegetable crops such as Brassicas, legumes, root crops and salad crops do well in well-drained peaty soils.
6. Loamy Soil
Loamy soil, a relatively even mix of sand, silt and clay, feels fine-textured and slightly damp. It has ideal characteristics for gardening, lawns and shrubs. Loamy soil has great structure, adequate drainage, is moisture retaining, full of nutrients, easily cultivated and it warms up quickly in spring, but doesn’t dry out quickly in summer. Loamy soils require replenishing with organic matter regularly, and tend to be acidic.
Great for: Climbers. bamboos, perennials, shrubs and tubers such as Wisteria, Dog’s-tooth violets, Black Bamboo, Rubus, Delphinium. Most vegetable crops and berry crops will do well since loamy soil can be the most productive of soil types. However, loamy soil requires careful management to prevent depletion and drying out. Rotating crops, planting green manure crops, using mulches and adding compost and organic nutrients is essential to retain soil vitality.
Simple Tests to Help Determine Your Soil Type
The water test
Pour water onto your soil. If it drains quickly it is likely to be a sandy or gravelly soil. On clay soils the water will take longer to sink in.
Squeeze test
Grab a handful of soil and softly compress it in your fist.
If the soil is sticky and slick to the touch and remains intact and in the same shape when you let go it will be clay soil.
If the soil feels spongy it’s peaty soil; sandy soil will feel gritty and crumble apart.
Loamy and silty soils will feel smooth textured and hold their shape for a short period of time.
Settle test
Add a handful of soil to a transparent container, add water, shake well and then leave to settle for 12 hours.
Clay & silty soils will leave cloudy water with a layer of particles at the bottom.
Sandy soils will leave the water mostly clear and most of the particles will fall, forming a layer on the base of the container.
Peaty soils will see many particles floating on the surface; the water will be slightly cloudy with a thin layer at the bottom.
Soils that are chalky will leave a layer of whitish, grit-like fragments on the bottom of the container and the water will be a shade of pale grey.
If the water is quite clear with layered particles on the bottom of the container with the finest particle at the top – this soil is likely to be a loamy one.
Acid test
The standard pH for soils usually ranges between 4.0 and 8.5. Plants favor soil which has a pH between 6.5 and 7 because this is the level where nutrients and minerals naturally thrive. You can buy a simple pH test kit here, or from a local garden center. As a general rule, in areas with soft water you will have acid soil and hard water areas will tend to have alkaline soil.
Soil test kit
Use a soil test kit to assess primary nutrients (N-P-K), essential minerals, pH levels, and the presence of other chemicals. By testing your soil, you determine its exact condition so you can fertilize more effectively and economically. Soil should be tested periodically throughout the growing season.
BOULDER AREA SOIL TEST KIT: The University of Colorado (CU) campus at Fort Collins has a mail in soil analysis test available for $35. You can get the plastic containers at McGuckins Hardware to put your soil sample in, fill out the form, include a check, and mail it in. Your detailed soil analysis results will be returned within weeks showing where you can amend it to your needs.
How to make the most of your soil, whatever the type
Plants generally prefer neutral soil but it’s worth bearing in mind that some favor slightly acid or alkaline soils. Regardless of the pH of your soil it is possible to adjust the level slightly to make it more hospitable to the type of plants you want to grow. Remember this is only temporary, so it’s advised to make the most from the soil type you have.
Adding ground lime to your soil will make it more alkaline and aluminium sulfate or sulfur will help to make your soil more acidic.
If your soil is low in nutrients (like sandy soil), try supply it with organic matter such as compost and manure to enrich the soil and improve its texture. Use organic mulches such as straw, dried grass clippings and deciduous leaves. These mulches break down and incorporate into the soil, building a new supply of organic nutrients while improving the soil structure.
Clay soil is often not aerated enough and is deficient in good structure which makes it more difficult for successful growing. To get the most out of clay soil it’s best to add large quantities of well-rotted organic matter in the fall and peat a few weeks before planting. Greensand can also be used to loosen heavy clay soils or bind sandy soils.
It is often difficult to cultivate in chalky soil due to its alkaline nature. To help rectify this add bulky organic matter which breaks down over time, adding nutrients and minerals to the soil.
Make sure your soil is healthy.
It’s a good idea to regard your soil as living as well as your plants – it too needs food and water. Make sure it contains the three main nutrients: Nitrogen, Phosphorus and Potassium (NPK) which are vital to growing plants effectively. Organic matter and fertilizers are rich in these.
After a crop is harvested the soil needs to be renewed before planting a successive crop. Many gardeners plant ‘green manure’ crops such as legumes, buckwheat, vetch and clover which fix nitrogen into the soil while building texture, improving aeration and drainage and adding organic matter. These cover crops are tilled in before they go to seed, and break down quickly so a new harvestable crop can be planted without much delay.
Crop rotation, green manures and cover crops, the use of mulch and the periodic addition of organic materials like compost and fertilizer are standard ways of restoring soil health after crop harvests. Rock phosphate, or rock dust, is also a valued amendment to restore phosphorus levels needed for vigorous plant growth.
If you can, introduce and encourage living organisms to your soil. The fungus Mycorrhize will aid your plants in the absorption of water and nutrients and worms will help speed up the composting process and help spread fertilizer through the soil.
When you first start out this can all seem very complicated but by identifying your soil type it will make the growing and maintaining of a healthy garden a lot easier. Remember, it’s well worth the trouble as your soil type is never going to change!
