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Gardening: Plants ready for fertilizer boost to keep on growing

Another week of warm weather is passing, and it doesn’t look like cooler weather is anywhere to be found in the forecast.

That means our gardens are growing like mad and the plants are using up their food reserves quickly. They are probably in need of a good dose of fertilizer about now.

Our roses have been beautiful all summer and some of them will continue to bloom into the fall. However, fall and winter aren’t all that far off, so it’s time to start preparing for the cold.

Roses should be fertilized for the last time by late July to very early August with a 20-20-20 liquid rose food. The numbers represent nitrogen for leaf growth and potassium and phosphorus for root and flower growth. Applying fertilizer now allows the new growth generated from the application to grow and harden off before the hard frosts hit. Liquid fertilizers are better than granular ones this time of year because the liquid nutrients are available immediately to the plants.

Plantings of annuals, especially those in containers, need regular fertilizing. Annuals in containers need to be fed every other week with a half-strength 20-20-20 liquid or granular fertilizer. This keeps fertilizer levels even but won’t generate massive green growth.

Annuals planted in flower beds can be fertilized once a month with a 20-20-20 liquid or granular fertilizer. Liquid fish and kelp, blood meal and alfalfa pellets worked into the soil will release their nutrients slowly.

Heavy-feeding vegetables such as corn, tomatoes, peppers, eggplant, cucumbers, melons, pumpkins, potatoes, squash and celery require a soil rich in organic material and regular feeding through the growing season. Now that most of them are getting ready to set fruit, it is important to make sure they have enough nutrients to produce abundantly.

Apply a 5-10-10 fertilizer as a side dressing to plants and work it into the top inch or so of the soil once a month until production is over. Water in well, especially if it is a dry granular fertilizer. Liquid fertilizers can be applied as a foliar spray that will be absorbed directly by the leaves. Organic fertilizers such as fish, blood and kelp meals and liquid sprays will release their nutrients more slowly than conventional fertilizers and will be of a more long-term benefit to the plant.

Now is a good time to start thinking about your vegetable garden rotations for next year. The heavy feeders listed above should be planted in areas that are growing beans and peas this year, and root crops should be planted where the heavy feeders were this year. Give berry crops a side dressing after they finish producing to build resources for next year.

You should wait until early spring to fertilize shrubs and trees, as they have finished their growth for the year and in another month will start preparing for fall and then winter. Most shrubs can be fertilized from mid-March into May, but rhododendrons should be fertilized just before the buds emerge.

Pat Munts has gardened in the Spokane Valley for more than 35 years. She can be reached at