Q: My garden didn’t flourish last summer. Does it need a lot of fertilizer this spring?
—Marv and Pet Daniels, Pismo Beach
A: It’s hard to judge why plants don’t perform as we hope. Lack of nutrients could be a problem. Sandy soils contain few nutrients and require more feeding as rain and irrigation water leaches fertilizers away quickly. Clay soils usually retain many nutrients, but they may not be available to plants when the soil is wet or cold, or compacted.
Amending soil with organic matter not only increases the soil’s potential for holding nutrients but also improves soil aeration, water infiltration, and water retention.
Vegetables planted in well amended soil (as well as annual flowers and roses) will probably need supplemental feeding every six to eight weeks. Perennials would be happy with a dose of nutrients now and another later in the summer, depending on soil texture and organic matter content. Healthy established trees and shrubs probably need no additional feeding, Native plants also do better without fertilization.
Plants cannot distinguish between nourishment provided by inorganic or organic (such as compost and manures) fertilizer.
Inorganic fertilizers provide nutrients quickly but may rapidly leach from soil. Of the ingredients in inorganic fertilizer, nitrogen is the most commonly needed for growth. Inorganic fertilizers usually offer three primary nutrients (nitrogen, phosphorus and potassium). Some gardeners will apply just nitrogen (such as ammonium nitrate and ammonium sulfate) for a quick, inexpensive fix.
Any fertilizer may burn plants if misapplied, especially those high in nitrogen. Follow packaging directions as to quantities and avoid over-fertilizing to prevent leaching of nitrogen into water supplies.
Slower-acting organic fertilizers may provide other needed micronutrients and will improve soils when dug in. Most gardeners find that it is appropriate to use both organic and inorganic fertilizers depending on garden conditions.
The best advice for feeding your garden: Know your plants, watch for signs of nutrient depletion— and ask your local Master Gardeners for advice or go online: http://groups.ucanr.org/cagardenweb/general.Click on ‘Gardening Basics,’ and then ‘Managing Soil and Fertilizer.’