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Gardening: Enjoying May in Northwest gardens

May in Northwest gardens by Mary Robson, Area Horticulture Agent, WSU Extension
May! Finally! After a dark, intermittently rainy April, gardens and gardeners are ready for the sunny season. Even with cloudy days, western Washington is alive in May with blooming shrubs and the unfolding rush of perennial flowers like peonies.
   Warm-season annual flower plants like marigolds, geraniums, and petunias can go out into garden containers and flower beds after about mid-Month. The traditional "flower basket" day is usually Mother's Day, when nurseries overflow with color and people hang flowering baskets. Annuals set out earlier may not grow much until the soil begins to warm.
   Remember to "harden off" flower and vegetable nursery plants that have come out of warm sheltered greenhouses. Expose the baby plants to cooler air and wind gradually; set them outdoors during the daytime only, in a sheltered warm place for the first two days, bringing them in at night. Gradually extend the exposure over a week until they are ready to spend the night outdoors and be planted out. If plants go directly from protected growing areas into outdoor planting, they may grow slowly and may also exhibit "cold symptoms" like reddening of the leaves. Remember that many annual flowers are natives of warmer climates like Central America and South Africa, and don't thrive in cool regions unless carefully handled.
   When selecting nursery plants, choose sturdy, stocky deep green ones. Smaller annuals will catch up with taller plants easily, because their root systems adapt well to transplanting. The largest flowering annual isn't always the best purchase for garden color and flower baskets. Look for well-branched plants with good bud set. Flowering annuals will come into full bloom and production about six weeks after they are set out.
   Tomato plants will be ready for outdoor life between mid-May and the first of June. The King County Master Gardeners usually set their transplants out in their Demonstration Garden in Bellevue the first weekend in June. If tomatoes are set out earlier, it will help to provide some shelter to keep temperatures warmer at night. A simple method is to place a wire "tomato cage" over the plant and then drop a plastic bag over the plant at night, removing it in the morning until night temperatures really warm.
   Incidentally, a wire cage may provide enough support for the smaller tomato cultivars, but if the tomato is going to be a scrambling monster, consider constructing a sturdier wooden support.
   Choose tomatoes that are willing to ripen in local cool summers. Some that have good productive possibilities are "Early Girl," "Stupice," "Oregon Spring," Fantastic," and "Celebrity." For gardeners who grew up in the Midwest (as I did), munching "Big Boy" tomatoes the size of basketballs and with the sweetness of brown sugar, eating tomatoes grown in the maritime Pacific Northwest can require a serious attitude adjustment. Use the appropriate tomato cultivars and give them as much shelter and sun as possible. Consider taking them to tanning parlors. (Just kidding.)
   Squash, cucumbers, melons and other warm-weather crops can also be set out in late May. Exact timing will vary depending on how sheltered an individual garden micro-climate is. Using plastic covers over tender crops for the first three weeks they are out is a beneficial assist to their growth.
   Incidentally, during a visit to northern Scotland in July, I noticed that all the warm-weather crops in that cool-weather area are grown INSIDE greenhouses. I didn't see a single tomato out in the open fighting cool temperatures.
   May still offers time to fertilize perennials, trees, and shrubs if they haven't been putting on enough growth. A general purpose 5-10-10, applied at the rate suggested on the package, will provide a good boost for most maritime Northwest plants. Do not over-fertilize, especially with high-nitrogen formulas like 20-20-20 (20% nitrogen, 20$ phosphorus, 20% potassium). Too much nitrogen fertilizer can lead to a lot of soft, weak tip growth that is then subject to aphid attacks and may also be more susceptible to some disease organisms. Spread compost as a mulch after fertilizing, and do not fertilize dry soil without watering it in well. A good time to fertilize is between rainy days!
   You may observe "spittle bugs," the unattractively but accurately named critters that hunker down on plants under a coating of frothy spit-like bubbles and often show up in May. They aren't generally harmful, but they are an aesthetic nuisance. Under the bubble there is a little greenish-yellow insect which is easy to squish by hand (wearing, of course, rubber gloves). A firm spray of water will also wash them off. Insecticides don't penetrate the froth well, so squish, squeeze, or spray these off. Or ignore them. This is a transient pest that will move into the next life stage and be unnoticeable by mid-June.
   Aphids--well, there's a real insect problem. Check tender new growth on roses, perennials, and vegetables for thick infestations of aphids. Aphids are sucking pests, and they weaken plants by drawing out plant juices. They may also cause deformed leaves by injecting toxins into the plant, or by carrying viral infections.
   The aphid has a lot of natural enemies that will help reduce their populations. Birds, ladybugs, lacewings, wasps, and other beneficial predators thrive on aphids. My opinion is that having some in the garden helps encourage beneficial predators to stick around. If they are multiplying faster than the beneficials are controlling them, wash them off every other day with a spray of water. Or use insecticidal soap, but don't use it in the hot sun. It can damage new growth. Insecticidal soap is effective against aphids but has to be used often; check every four or five days.
   Fertilize rhododendrons and azaleas again after bloom with an acid-based fertilizer formulated for these shrubs. If you can, removing the spent flowers may help in both tidying up the plant and preventing seed from forming. Sometimes this also helps with new blooms for the following year, but it's really more an effort to improve the plant's appearance.
   The most definite need of rhododendrons and azaleas is sufficient water during summer dry spells. Next year's buds will be set on the plant during late July and August, and if the plant dries out, bloom will be scarce. Prune spring-flowering shrubs immediately AFTER bloom.
   The rush of growth in May also invigorates gardeners; even with lots of garden chores at hand, take time to sit outside in the longer evening light appreciating the flowering of life again.

Visit WSU's Agriculture Site on the World-Wide Web at http://www.cahe.wsu.edu.