Dry Organic Fertilizers
Dry organic fertilizers can consist of a single material, such as rock phosphate or kelp (a type of nutrient-rich seaweed), or they can be a blend of many ingredients. Almost all organic fertilizers provide a broad array of nutrients, but blends are specially formulated to provide balanced amounts of nitrogen
, potassium, and phosphorus, as well as micronutrients. There are several commercial blends, but you can make your own general-purpose fertilizer by mixing individual amendments.
Applying dry fertilizers
The most common way to apply dry fertilizer is to broadcast it and then hoe or rake it into the top 4 to 6 inches of soil. You can add small amounts to planting holes or rows as you plant seeds or transplants. Unlike dry synthetic fertilizers, most organic fertilizers are nonburning and will not harm delicate seedling roots.
During the growing season, boost plant growth by side-dressing dry fertilizers in crop rows or around the drip line of trees or shrubs. It’s best to work side-dressings into the top inch of the soil.
Liquid Organic Fertilizers
Use liquid fertilizers to give your plants a light nutrient boost or snack every month or even every 2 weeks during the growing season. Simply mix the foliar spray in the tank of a backpack sprayer, and spray all your plants at the same time.
Plants can absorb liquid fertilizers through both their roots and through leaf pores. Foliar feeding can supply nutrients when they are lacking or unavailable in the soil, or when roots are stressed. It is especially effective for giving fast-growing plants like vegetables an extra boost during the growing season. Some foliar fertilizers, such as liquid seaweed (kelp), are rich in micronutrients and growth hormones. These foliar sprays also appear to act as catalysts, increasing nutrient uptake by plants. Compost tea
and seaweed extract are two common examples of organic foliar fertilizers.
Applying liquid fertilizers
With flowering and fruiting plants, foliar sprays are most useful during critical periods (such as after transplanting or during fruit set) or periods of drought or extreme temperatures. For leaf crops, some suppliers recommend biweekly spraying.
When using liquid fertilizers, always follow label instructions for proper dilution and application methods. You can use a surfactant, such as coconut oil or a mild soap (¼ teaspoon per gallon of spray), to ensure better coverage of the leaves. Otherwise, the spray may bead up on the foliage and you won’t get maximum benefit. Measure the surfactant carefully; if you use too much, it may damage plants. A slightly acid spray mixture is most effective, so check your spray’s pH. Use small amounts of vinegar to lower pH and baking soda to raise it. Aim for a pH
of 6.0 to 6.5.
Any sprayer or mister will work, from hand-trigger units to knapsack sprayers. Set your sprayer to emit as fine a spray as possible. Never use a sprayer that has been used to apply herbicides.
The best times to spray are early morning and early evening, when the liquids will be absorbed most quickly and won’t burn foliage. Choose a day when no rain is forecast and temperatures aren’t extreme.
Spray until the liquid drips off the leaves. Concentrate the spray on leaf undersides, where leaf pores are more likely to be open. You can also water in liquid fertilizers around the root zone. A drip irrigation
system can carry liquid fertilizers to your plants. Kelp is a better product for this use, as fish emulsion can clog the irrigation emitters.
Using Growth Enhancers
Growth enhancers are materials that help plants absorb nutrients more effectively from the soil. The most common growth enhancer is kelp (a type of seaweed), which has been used by farmers for centuries.
Kelp is sold as a dried meal or as an extract of the meal in liquid or powdered form. It is totally safe and provides some 60 trace elements that plants need in very small quantities. It also contains growth-promoting hormones and enzymes. These compounds are still not fully understood, but are involved in improving a plant’s growing conditions.
Applying growth enhancers
Follow the directions for spraying liquid fertilizers when applying growth enhancers as a foliar spray.
You can also apply kelp extract or meal directly to the soil; soil application will stimulate soil bacteria. This in turn increases fertility through humus formation, aeration, and moisture retention.
Apply 1 to 2 pounds of kelp meal per 100 square feet of garden each spring. Apply kelp extract once a month for the first 4 or 5 months of the growing season.
If fresh seaweed is available, rinse it to remove the sea salt and spread it over the soil surface in your garden as a mulch, or compost it. Seaweed decays readily because it contains little cellulose.