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News / Life / Clark County Life

Gardening with Allen: When and how often to fertilize

By Allen Wilson, Columbian freelance writer
Published: May 11, 2024, 6:08am

Last week I described the basic fertilizers that I use. This week I will add information about when and how often to fertilize different kinds of plants.

Lawns: Frequent fertilization is needed to keep lawns looking nice for the whole growing season. Lawn fertilization companies make applications at six-week intervals. If you apply fertilizer in September or October it will not only keep the lawn green through the winter but will carry over in the early spring so you can wait until May for a spring application. If you use a lawn fertilizer in which part of the nitrogen is coated for slow release, the May application will last through the summer. Without slow release nitrogen a third light application should be made in mid-summer.

Trees and shrubs: One fertilizer application in the spring is normally adequate for trees and shrubs. I usually apply lawn fertilizer at the same time I fertilize the lawn. Newly planted trees and shrubs should be fertilized with a general purpose fertilizer at the time they are planted.

Vegetables: I fertilize with a general purpose fertilizer at the time they are planted. Most root and leaf vegetables only need one application. Vegetables that are harvested over a longer period, like tomatoes, peppers, squash and cucumbers may need a second application about six weeks after planting. One application of Osmocote is usually enough. Osmocote is a timed release fertilizer that lasts three to four months.

Flowers: Unless I use Osmocote, I make a second application to annual flowers about six weeks after planting. I sometimes make a second application to late blooming perennial flowers. I make 2 applications to flowers in containers. If I use Osmocote, I make a second application about three months after planting.

Reducing Acidity: Soils and water in Western Washington and Oregon are naturally acid. Most plants will grow better if soil pH is brought back to a more neutral level. Lime will make natural occurring iron more available to plants and will reverse yellowing caused by iron deficiency. I like to apply lime at the rate of 3 to 5 pounds per 1,000 square feet every year or two to flowers and vegetables. Even vegetable beds with artificial soil mix can benefit from a light lime application because of our acid water. Trees, shrubs and lawns would benefit from applications every second or third year. Wherever possible, lime should be mixed into the soil with a hoe or rake. I mix a liberal amount of lime with the soil around newly planted plants.

Columbian freelance writer