Question: You recently suggested fertilizing lawns in March. Is that also a good time to fertilizer other plants?
Answer: Yes, now is also an excellent time to fertilize all the permanent plants in your garden including trees, shrubs and perennial flowers. Roots are active and will pick up the fertilizer and convert it into usable nutrients for spring leaf growth.
Although there are many specialized fertilizers available, I use two types for almost all my outdoor plants. I use lawn fertilizer for my lawn, trees, and shrubs, and a general purpose fertilizer for flowers and vegetables.
Typical lawn fertilizer formulas have about three to five times as much nitrogen as potassium and no phosphorus. A typical balance of nitrogen-phosphorus-potassium would be 15-0-5 or 25-0-5. Organic fertilizers will have a lower percentage with about half as much fertilizer. It is also important to have a small percentage of iron and sulfur (3 percent or less is enough).
Since nitrogen is the most soluble of nutrients, it is also desirable if at least part of the nitrogen in lawn fertilizers is of the slow release or timed release type. This is often accomplished by coating or encapsulating the nitrogen pellets. This allows the nitrogen to be released over a longer period, reducing the need for frequent applications. Look on the fertilizer label to see if part of the nitrogen has been “polymer coated.”
Although many tree and shrub fertilizers have different nutrient balances, I have found that lawn fertilizer works equally well, and sometimes better. General purpose fertilizers are also suitable for trees and shrubs.
General purpose fertilizers usually contain about a 1-1-1 ratio of nitrogen- phosphorus-potassium. Typical is 12-12-12 or 16-16-16, with organic fertilizers more like 6-6-6. These ratios do not have to be exact, just so there are approximately equal amounts of the three major fertilizer nutrients. Micro-nutrients such as iron, and zinc are also beneficial. I have found that general purpose fertilizers work equally well for flowers and vegetables as special flower and vegetable fertilizers.
General purpose fertilizers are also available in a coated or time-release type. I use them for all my containers and sometimes in flower beds. Osmocote is one commonly available brand. I generally prefer granular over liquid fertilizers because they are cheaper and longer lasting.