Choosing A Main Meal Fertilizer
All plants need, as major nutrients, nitrogen (N), phosphorous (P), and potassium (K). These primary nutrients plus small amounts of other elements called micronutrients--magnesium, calcium, boron, and other chemical elements found naturally in soil--are all present in "general purpose" fertilizers. So these all-purpose or general purpose fertilizers can be used for the main meal for all plants in home landscapes.
There are a number of different types of these general purpose fertilizers. While they all provide essential nutrients for trees, shrubs, lawn grass, flowers and ground covers, they differ in formulation, cost, availability, method of application, and duration of effectiveness.
Granular vs. Liquid - Granular fertilizers (that have slow acting nitrogen) make the best main meal because they release nutrients slowly, maintaining a steady supply over the season. Use liquid fertilizers, packaged as either powders that are to be dissolved in water or in liquid form, for optional snacks for certain plants.
Type of Nitrogen - The nitrogen in fertilizers may be either quick acting or slow release. These terms indicate how quickly the nitrogen is made available to plants. There are advantages to each type. All liquid fertilizers and many granular products have quick acting nitrogen. They take effect rapidly, the plants showing obvious greening and new growth within days. However, the nitrogen is depleted rapidly too, so more fertilization is necessary to maintain the level of nutrition.
Increasingly, granular fertilizers are incorporating a slow release or "slow action" form of nitrogen. These products release the nitrogen slowly, sustaining a uniform supply over many, many weeks. They make the best main meal. Check the small print on the package label to assure that over 50% of the nitrogen will be what is called "insoluble nitrogen" (it dissolves into the soil very slowly). Slow release nitrogen is not wasted through leaching. It does not burn either the plants or the earthworms. Slow release type nitrogen fertilizers are usually more expensive than quick release types of products.
Synthetic vs Natural - While you may wish to use "organic" or natural fertilizers, particularly in the vegetable garden, we feel that the issue of whether the nitrogen is slow release type is more important than whether the product is made of synthetic materials or natural materials. It turns out that most of the slow release products happen to also be made of natural materials however.
Note - A growing number of communities in the United States are processing their sewerage sludge into safe, effective, general purpose fertilizer. There is no danger of heavy metals and this fertilizer is a good as any other commercial product for feeding your landscape. Milorganite is an example of one of these fertilizers.
NPK Numbers - The label on any bag or box of fertilizer indicates the percentages of the primary nutrients--(N)itrogen, (P)hosphorus, (K)potassium--by three numbers, e.g. 5-10-5. Serious gardeners often select fertilizers for specific plant groups, seeking fertilizers very heavy on one nutrient as opposed to another to suit that plant's special circumstances.
Homeowners need not worry about the NPK numbers on their fertilizer bag. Any product sold as "general purpose" fertilizer will benefit all plants, including lawns. For a product suited to a specific plant, choose one labeled for roses, acid loving plants, bulbs, fruit trees, etc.
Main Meal For Lawns
See the file Fertilizing Lawns for more details. The first issue in selecting a lawn fertilizer is whether you leave the clippings on the lawn when you mow it. Grass clippings contain one to two percent nitrogen. When left on the lawn, they can contribute up to 40% of your lawn's seasonal fertilizer needs. Whether you leave the clippings or not controls how much fertilizer you need.
The most effective fertilizing program is two main meals, once in the fall and again in the spring. For a lower maintenance lawn, eliminate the spring fertilizing. While the spring grass will not be quite as green, it will still be very healthy. The fall feeding builds strong roots to sustain it all year. The clippings provide nitrogen throughout the growing season. Lawns growing in shade should get less fertilizer than lawns growing in the sunshine.
If you use a quick acting nitrogen fertilizer (either granular or liquid) on your lawn, make four applications to get the equivalent benefit of the two applications of slow release nitrogen fertilizer. Time them as carefully as possible so that the grass gets a continuing supply of nitrogen and does not suffer sudden or prolonged deprivation of it between feedings.
Main Meal For Flowers & Vegetables
The best time to give flower beds and vegetable gardens their main meal is the early spring before the plants have filled in the bed. One main meal of slow release fertilizer is usually sufficient for low maintenance gardens. For high performance gardens, give two main meals of slow release fertilizer, one in early spring, and another sometime in June. Every plant file in Yardener’s Helper has a section dealing with fertilizer needs for each plant; flowers, foliage, and vegetables.
Main Meal For Trees, Shrubs, Hedges
For more details see the files Fertilizing Shrubs and Fertilizing Trees. Fall is best time to feed main meals to trees, shrubs, and hedges. While you may not wish to feed large trees and well established shrubs, it is very important to fertilize young trees and shrubs for the first two or three years after planting. Spread slow release nitrogen fertilizer on the soil or mulch out to, and a bit beyond, the drip line of the tree or shrub sometime in September or October. A spring feeding in April or May is optional but will definitely help these plants.
As a rule of thumb, fertilize any large tree that has not been fed for three to five years, or that is not growing at a normal rate.
To fertilize trees effectively, it is important to understand how their roots are structured. A tree's root zone spreads over an area about a third again larger than the breadth of its branches. Like the branching pattern of its canopy, the larger roots of a tree are nearest the trunk and the small fibrous hair roots that actually pull in the nutrients are farthest away. So, the roots that actually feed the tree are in a circle beginning about a foot or two from the trunk and continuing to several feet beyond the spread of the branches. It is important to spread fertilizer in this zone. If it is put any closer to the trunk, it is likely to be wasted.
Once ornamental and shade trees reach maturity it is difficult to feed them effectively. It is recommended that professional arborists be hired to evaluate and feed valued specimens and those trees that have health problems.
Tree spikes, designed to be pounded down into the soil around the tree, are not effective in providing a large tree with all the nutrients it needs. Homeowners should use a standard slow release all-purpose granulated fertilizer for more satisfactory results. Sprinkle this on the soil over the root zone for the rain to soak in. The size of the tree trunk determines how much fertilizer is needed. Read and follow package instructions.