If you suspect that your soil may be causing poor plant growth, first check to make sure the cause is not a physical problem such as:
- over or under watering
- disease or pest infestations
- soil compaction (that impedes air, root, and water movement)
- a hard layer (hardpan) that prevents water draining through the root zone. Poor drainage reduces air between soil particles. Without air, roots suffocate, plants can't absorb water and, molds and rots kill plants.
The ability of the soil to hold water is called water holding capacity. Water holding capacity is affected by a variety of factors, most importantly: organic matter, compaction, and texture.
Soils that are well managed help produce healthy plants that are less susceptible to pests and disease. To improve soil and replenish plant nutrients, apply fertilizers, either organic types such as compost and manure or chemical amendments. Compost is the preferred amendment, because it is made of organic matter that has undergone the decomposition process, so nutrients are readily available for plant use.
Compost contains micronutrients, nutrients that are needed in small amounts, yet are essential for plant growth. Compost increases soil biological activity, waterholding capacity, and creates a crumbly, tillable medium for air, root, and water movement. To improve sandy or clay soils, till compost or organic matter into the top 6-8 inches of soil before planting.
Chemical fertilizers dissolve in water easily, so they can flow away in runoff. When using chemical fertilizers, apply the correct amount and at the right time. Consider weather conditions and timing of applications. Apply fertilizers during the plant's growing season, and not during heavy rains.
Additionally, too much fertilizer too fast, leads to excessive plant growth. By applying the correct amount or by using slow release fertilizers, you limit an excess of new plant growth that would invite pests. Because nitrate-N is highly soluble in water, it may leach (drain below the root zone), especially in course-textured sandy soils. Split applications of nitrogen fertilizer help reduce the nitrogen loss to leaching.
Fertilizer Selection and Use
Plants need many chemical elements, but nitrogen (N), phosphorus (P), and potassium (K) are needed in the greatest amounts. Chemical fertilizers are prepared in proportions of N-P-K, and their percentages are labeled on fertilizer bags, for example 16-20-0 is 16% nitrogen, 20% phosphorus, and 0% potassium. To calculate the pounds of actual nitrogen, multiply its percentage by the total weight of the bag of fertilizer.
Learn about soil health here.