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Cool April weather this year has given our gardens extended spring beauty. Tulips and daffodils bloom on. Their flowers lasting longer than usual. But May will bring the rush of unfolding growth that ends the quiet of early spring and replaces it with the clamor of summer. Now plants grow so quickly we see garden changes from day to day.
During May, planting from nursery containers works well to add new shrubs and trees to the garden. Wandering through nurseries, I enjoy selecting spring shrubs in bloom to add dimension to the garden. Not long ago, my artist aunt did a watercolor of the garden, adding masses of color where she saw gaps. Now I'm planting to carry out her artistic vision.
Is it too late to transplant a tree or shrub? In the case of deciduous plants, wait until all leaves have opened fully. It's tricky because moving or transplanting established plants isn't as successful when done this late in the year, although it can be done with very careful attention to watering. Broadleaf evergreens such as rhododendrons are a little easier to move now, but again summer care and watering helps their survival.
Keep weeding in May. Gardeners fight the remarkable ability of a weed to hide under a plant and emerge full grown with seeds and deep roots. Once soils warm a bit, place or replace mulches around the garden to keep annual weed seeds hiding in the soil from germinating. Neglected weeds now grow to monsters by July.
Garden soils remain cool, even cold in places. If purchasing tender flowers such as marigolds, petunias, or geraniums, be sure to provide protection from chilly temperatures when nights are still down in the 30s and 40s. Think of the difference between a cozy heated greenhouse and the exposed cold garden at night. Plants need help making the transition when they are brought out of nurseries or taken from an indoor growing area.
The process of adjusting plants to cool weather is strangely called "hardening off," and means toughening up the plants. First, set the plants out in a warm, sheltered area during the day. Then take them in at night. Do this for two or three days. Expose the plants during the day to a slightly cooler area, with more wind exposure. Once the plant is outside, cover at night with plastic (like an unfolded plastic garbage bag) for protection. After about a week, the plants will have acclimated. Summer annuals and tender vegetables planted in cold weather won't grow well, and will often develop purplish leaf coloration.
Plan to keep container plants for summer color watered regularly and fertilized every three weeks. The process of watering leaches nutrients away from the roots, so renewal fertilization is vital for summer color spots. Many gardeners incorporate a timed-release fertilizer when planting. This helps, because most potting soils in bags seldom contain plant nutrients.
The bedding plants you buy, looking green and healthy, have received regular doses of fertilizer at the nursery while growing. They need it to sustain healthy growth. What you choose to fertilize with doesn't matter as much as using it regularly. Look for one containing "trace elements"--as well as the nitrogen, phosphorous, and potassium that all fertilizers will have. Do not over fertilize with too much nitrogen, which will lead to leaves rather than flowers and fruit.
Check soaker hoses and irrigation systems now. Water conservation, always vital, will be especially important as stream flows are needed for salmon protection. Be sure to over-ride automatic systems to keep them from wasting water during rainy periods. In May, plants grow quickly. They need both water and nutrients. Rhododendrons and other spring-blooming shrubs require water in May to support bloom and new leaf expansion. If rainfall is less than 1 inch per week in May, be sure to irrigate plants.
When watering, be sure to apply water slowly and gradually, allowing it to seep down into the soil's roots.
Transplants of the warm weather vegetables such as squash, tomatoes, eggplant, and peppers should be growing inside. If they've not been started, plant those seeds indoors immediately. Those warm-weather lovers must stay indoors, or should ideally stay indoors, until soil temperatures have warmed, hopefully into the 50's. Many Washington State University Demonstration Gardens don't set out tomatoes and squash out until the first weekend in June.
Dogwood trees may begin to show signs of the common fungal disease, dogwood anthracnose, as the leaves and blooms open in May. The leaves will show spotting and browning, usually starting at the leaf end tip and moving up along the mid-rib. Pruning out affected branches, if practical, can be helpful. Keep all fallen leaves raked and do not dispose of them in home compost. If you wish to spray, choose a registered fungicide such as fixed copper, and apply it to the leaves every ten days until dry weather sets in, spraying as the buds begin to open and continuing to apply it to expanding leaves.
Actually, many dogwoods can co-exist with the fungal disease and get along without spraying even though they may look less than perfect. Don't let the Eastern dogwood, Cornus florida, get too dry during summer. Be sure it gets deep watering at least once a month. Several attractive dogwoods, Cornus mas (Cornelian cherry) and Cornus kousa (Korean dogwood) are resistant to dogwood anthracnose. These trees make good choices for low-maintenance landscapes.
Allow the joy of May to alter your days. Start the day observing an expanding peony bud or new maple leaves. Winter, long wet and dull, can now become only a memory.
Hortsense: Managing plant problems with Integrated Pest Management
