inadequate soil aeration, inadequate moisture or waterlogged soil, planting too deeply, adverse climatic conditions, improper soil pH, nutrient toxicity or deficiency
The timing and method of fertilizer application depend on both the target plant species and whether the fertilizer is synthetic or organic.
|Synthetic Fertilizer||Organic Fertilizer|
|refined from natural ingredients or manufactured||natural form or minimally processed|
|known chemical composition||highly variable|
|immediate nutrient availability — an advantage in situations like the vegetable garden where needs are exacting and timing must be precise to supply nutrients during critical periods of growth, bloom, and fruiting||highly variable — must break down in soil before nutrients can be used, rate depends on soil temperature, moisture, pH, and microbial composition|
|improves soil structure|
benefits soil organisms
|ammonium sulfate, potassium chloride, monoammonium phosphate, processed urea||manure, cottonseed meal, cover crops, fish by-products, compost, bone meal, raw minerals|
|Adapted from the Master Gardeners of Grays Harbor & Pacific Counties, WA: Fertilizers|
Synthetic fertilizers usually act quickly and are more susceptible to leaching, so they are incorporated shallowly and applied more frequently, timed to coincide with plant growth, flowering or fruiting.
Organic fertilizers must be broken down by soil microorganisms before they can be absorbed by plants, so they are often incorporated to the depth of the bed prior to planting.
Remember, organic fertilizers are not intrinsically safer than inorganic products. They sometimes contain plant or human toxins:
Because of their relatively low nutrient content, organic fertilizers are applied at much higher rates than inorganic fertilizers. Therefore, even at the highest spreader settings you may have to make two or more passes over an area to apply the required amount of material. Avoid skips and overlap by applying ½ of the fertilizer while traveling in one direction and the remaining half while traveling in a perpendicular direction, or space piles of the material throughout the area and spread the piles out uniformly using a garden or leaf rake. To calibrate your spreader:
You can make an organic version of 10-10-10:
Mother Earth News A Better Way to Fertilize Your Garden: Homemade Organic Fertilizer
There are limits to what fertilizer can do. Your soil, mulch, and plant litter comprise a system that acts as a “bank” for nitrogen. Fertilizers, even organic fertilizers, are too mobile (they are either used, leached or volatilized) to build up the capital in this bank. For a healthy system, fertilizing should be complemented by improving the soil with compost.
Roadside Revegetation: Soil Nitrogen and Carbon
Following best practices when you fertilize both improves results and is kinder to the environment.
Calibrate your spreader to ensure that you are applying the correct amount and clean your spreader over grass, not the driveway. Improper fertilizer application, even when the fertilizer is organic, can contribute to surface and ground water pollution, induce a plant nutrient deficiency or toxicity, or cause salt burn.
Use a fertilizer that contains 30% or more of the nitrogen in slow release forms. Look for words such as: “water insoluble nitrogen (WIN)”, “controlled release nitrogen”, “sulfur coated urea (SCU)”, “IBDU”, “ureaformaldehyde (UF)” or “resin-coated urea”.
Apply needed nutrients only. This also can be less expensive than applying a complete fertilizer, which contains all 3 macronutrients (nitrogen, N; phosphorus, P; and potassium, K). Generally, trees and shrubs need a ratio of 3:1:1 of N:P:K, while flowering plants need a higher amount of P than N or K. Overapplication of nitrogen in particular can be harmful, causing growth that is easily damaged by insects, disease or cold snaps.
Remember that recently transplanted trees and shrubs or those that have experienced root disturbance cannot grow until the roots recover and will not benefit from fertilizer application. Recovery requires ~ 6–12 months per inch of trunk caliper for trees, so it may be several to many years before a larger tree resumes growth.
Nitrogen need depends on the stage of plant growth:
Don’t use products that combine fertilizer with a pesticide or herbicide, including preemergent herbicides like crabgrass preventer. Apply these separately and only if needed. In addition to the environmental benefits, you may prevent unintended damage to your plants. For example, dogwoods, redbuds, apples, forsythia, and roses are extremely sensitive to the herbicide dicamba. Because roots can extend far beyond the drip line, damage can occur even when application is distant from the plant.
Established trees and shrubs usually do not require fertilization yearly — every 3–4 years is recommended. Mature trees and shrubs require even less. Fertilizer need also varies with soil type and rainfall. Plants in well-drained soil, especially if low in organic matter, will require more fertilizer because leaching will be greater and also because root systems will be more extensive, so they can support greater top growth. Similarly, periods of high rainfall can lead to both more leaching and greater growth, both of which increase fertilizer need.
Incorporate fertilizer into the soil where possible and avoid using granular fertilizer if heavy rain is forecast. Digging a wide planting hole and thoroughly tilling the soil results in rapid plant establishment and better root growth. Tilling ensures that physical and chemical amendments are evenly distributed in the root zone. Equally important, tilling improves soil structure so that soil water can effectively dissolve and transport the nutrients you have so carefully added. The goal is to provide the roots with moist, well-drained, well-aerated, and fertile growing environment.
Because plants absorb nutrients best when their root systems are healthy and actively growing (spring and fall), the best time to apply fertilizer is about two weeks before these periods so that the nutrients can move into the root zone in time to be available for plant use. Summer feeding is not mandatory.
Fall fertilization and cold hardiness in landscape trees
Preventing runoff maximizes plant benefit and also saves money.
Fertilizer recommendations and techniques to maintain landscapes and protect water quality