Fertilizing plants can be a bit bewildering, but to get the most out of your plants, especially container plants, it is essential. Have you ever wondered why some people and places seem to have larger, fuller plants? The likely answer is regular fertilization and correct watering. While many plants will do OK with little or no fertilizer, they will reach their full potential only with the correct nutrition.
If you are planting into the landscape add the appropriate amount of fertilizer into the hole before placing the plant (consult the package for specific amounts). Be sure to mix the fertilizer into the soil at the bottom of the hole. Roots can be burned by direct contact with slow release fertilizer. If you are applying to an already established planting, top dress according to the directions on the package.
So should you use a water soluble or controlled/slow release fertilizer? In general I think most people are best served using a controlled or slow release fertilizer. You apply it once or in some cases twice a growing season and then just water as necessary. You don’t have to mix up fertilizer every week or two and your plants should be perfectly happy.
There are times when it makes sense to supplement your controlled release fertilizer with an application or two of water soluble fertilizer.
If you have plants in pots that are “heavy” feeders (those that need a lot of nutrition), such as Supertunias®, you may want to use a water soluble fertilizer every couple of weeks to boost the nutrition level. Heavy feeders planted in the soil are taking advantage of the native fertility of your soil and shouldn’t need the extra fertilizer.
If you have gone through a long rainy period or had a very heavy rainfall, an application of water soluble fertilizer will return some nutrition to your potting mix (what was there has likely washed away in the rain) and help your plants rebound.
If your plants have grown very large supplemental water soluble fertilizer may help them maintain lush growth.
Plants will only need fertilizer during active growth periods. So if the plants are dormant don’t bother feeding. If the plants are actively growing you should be fertilizing. Be careful not to over fertilize in early spring (only a problem with water soluble fertilizers) when cooler temperatures mean plants aren’t growing as much.