FERTILIZERS, AMENDMENTS, mulch, 6-10-10, 8-0-0, 20-20-20, — what does it all mean? Confused over what to feed your garden? You're
not alone. Unfortunately, there is no one easy answer to our plant's dietary
The best advice you have probably heard before, but it deserves repeating: feed your soil. We are encouraged to provide our bodies with a healthy, well-balanced diet. Your plants are also looking for a healthy, well-balanced diet, and that diet comes from the soil.
Grow your soil by adding amendments such as compost or well-rotted manure. Your goal is to build a soil that is teeming with life: earthworms, decaying plant material, microbes and fungi, all working in harmony to aerate the soil and provide complex minerals to support healthy plant growth. This won't happen overnight and is an ongoing process in even the
most vibrant garden.
To supplement our human diets, we often take a multivitamin composed of the most essential vitamins for human health. This is not unlike using a "complete" general-purpose fertilizer that contains a balanced dose of the three macronutrients, nitrogen (N), phosphorus (P) and potassium (K). You will find these three numbers on fertilizer plant labels, always listed in this alphabetical order. Nitrogen promotes lush green growth and overall plant health. Phosphorous helps develop healthy roots, fruit and flowers. Potassium is essential for stem growth and plant vigor. The numbers, such as 10-10-10, indicate that there is an equal percentage of these
three elements in the fertilizer. The remaining 70 percent will vary by
manufacturer; some will contain micronutrients and others just filler
When we identify a deficiency in our bodies, we often take additional supplements. Similarly, we can examine our plants to determine their needs. Like our own bodies, plants do not benefit by a surplus of nutrition supplements. As advised for our own health care: read the label and follow the directions. Overfertilizing can burn tender roots, cause spurts of weak growth that attract pests, result in underperforming plants, plant death, and crispy "fried" leaves. Additionally, excessive fertilizer leaches into our groundwater.
You might consider a professional soil analysis to determine the nutritional composition and the acidic or alkaline levels (pH) of your soil. There are home test kits, readily available at your local garden center, and more comprehensive testing available in commercial labs. A number of local labs can be found at http://ucanr.org/sites/SoCo/files/27431.pdf.
I prefer to use all organic fertilizers as they release their nutrients more gradually and help improve the structure of the soil. Synthetic fertilizers are fast-acting, but too rapid growth can attract pests, encourage a flush of bloom and result in a weaker plant.
Nutrition needs vary from plant to plant, species to species, and season to season. Annuals — [hose plants that complete their life cycle in one season, such as marigolds, petunias, impatiens and most vegetables — are the heaviest feeders as they must grow their entire root and plant structure in a very short time frame. They will benefit from being planted in fast-draining soil containing plenty of organic matter, with regular feedings of a balanced fertilizer.
Perennials — plants that come back each year, such as delphiniums, geraniums and chrysanthemums — also like regular feeding, but they have the advantage of starting each growth season with an already sturdy set of roots. They may benefit from a monthly feeding of a complete fertilizer during their growing season. Most established foliage trees and shrubs do not need to be fertilized after their first two or three years.
Camellias, rhododendrons and azaleas not grown in rich, acid soils need an infusion of acidic fertilizer, specifically formulated for their needs.
Notoriously "fussy and demanding" roses can be pampered with a recipe from Gail Trimble, Master Rosarian, on the Marin Rose Society website titled "Fertilizing for the fanatical rosarian (www.marinrose.org/fertilizing2.html).
Cymbidium orchids appreciate year-round feeding with a bimonthly application of a readily available, commercial orchid fertilizer, specifically formulated for growth this time of year, switching to a bloom formula as the label directions indicate.
Mediterranean herbs such as rosemary, lavender and sage are drought tolerant and vigorous growers. Twice yearly mulching seems to provide all the nutrients they need.
Summer is a period of rapid plant growth. With few exceptions, your garden will benefit from a 2- to 4-inch application of organic mulch. Take care not to apply the mulch too close to tender stalks. Once you have established a regular program of feeding your soil with mulch and compost, your days (and dollars) of fertilizing may dramatically diminish.
Always water plants the day before you fertilize and the day after to prevent burning.
Read the directions and follow them; more is not better
Before you invest your time, energy and finances and in a struggling plant, ask yourself: is this the proper plant for this location? Re-examine your garden. Select plants that work in your microclimate and provide them with the nutrition they need. Learn to love what succeeds in your little corner of the world.