The quality of your garden soil is an important consideration in growing heirloom fruits, vegetables and flowers as soils come in a wide variety of textures and materials. Soil texture describes the size of the mineral particles in your soil. Soil particles in order of size, from smallest to largest, are: clay, silt, fine sand, medium sand and coarse sand. The ideal garden soil (for most plants) is a loam soil, which carries particles of clay, silt and sand, plus organic matter.
Soil structure refers to the way soil particles bind together to form clumps. In soils with good structure the spaces between particles are large enough to ensure good drainage but do not dry too quickly. The best garden soil, loam soil, drains fast enough for root health but retains enough moisture for continued satisfactory growth. Adding amendments to soils will improve its structure and provide food for beneficial microbes.
Another consideration to address before you add amendments to the soil is to test the pH— the measure of acidity to alkalinity in your native soil. A pH of 7 is considered neutral and many plants are adapted to this condition. A pH above 7 is considered alkaline while a pH below 7 is considered acid. A pH test can serve as a guide to which plants you might be able to grow with ease and others that might be more difficult. It is easier to make soils more alkaline, but difficult to acidify them. Even though you may add sulfur or aluminum to your soil to acidify it, the subsoils beneath will remain alkaline and eventually the alkalinity will return, especially if your water is alkaline. This makes it difficult to grow plants such as camellias, rhododendrons and azaleas (which prefer acid soil) in regions with alkaline soil and water. Adding lime or crushed shells to acid soils will increase soil alkalinity.
One consideration in growing heirloom plants is to research soil amendment ingredients and practices used in the 19th century, as most of the plants still in existence from that era and before were selected under those soil conditions. I am an organic gardener using these time-tested methods and believe that building your soil is crucial to long term success. By amending your soil with such things as greensand, sulfur, bone meal, kelp meal and manure, you will enrich it and create a productive environment for soil bacteria. You can choose from composted cow, hog or horse manure, alfalfa meal, cottonseed meal and guano or chicken manure to add significant nitrogen to your garden soil. These all contain small levels of potassium and potash. Bone meal, hoof and horn meal are excellent sources of potassium. Kelp meal, wood ashes and greensand are significant sources of potash. Greensand also contains many trace minerals. Keep in mind that bone meal is somewhat alkaline and wood ashes are quite alkaline. Home made compost is always valuable and usually contains a fair amount of nitrogen with smaller mount of potassium, potash and trace minerals. Another option to improve soil is to plant cover crops and till them under. Clover, rye, lentils, field peas, vetch and buckwheat are some examples.
This is the time of year to plan for improving your soil. As soon as the ground thaws you can test the pH and as soon as soil becomes workable (not too wet to dig) you can add amendments. It is important to learn as much as you can about what type of soil each plant you plan to grow prefers, for long term success. For example, brassicas (cole crops like cabbage) have fewer pest problems and greater production in slightly alkaline soils.