Spring comes early to Napa Valley
April is always a tricky time for the gardener eager to start summer planting. Remember last year when we had several 90ºF days at the end of April? No one knows what the month has in store for us. Have we seen the last of the rain, or will it turn cool and wet again?
We've already experienced more than a week of warm weather in Napa Valley, with temperatures in the high 70s and low 80s. It even hit 90ºF on a front porch in Calistoga. Such a heat spell can fool gardeners impatient to plant. But there is still the possibility of frost, especially at the northern end of the valley, even into May. And the soil may still be cold and sticky. So keep this in mind before being tempted by the tomato seedlings and summer annuals in the nurseries.
Gardeners need to be especially aware of their environment this month. Before planting any warm-weather crops, make sure the soil is at least 65ºF in the morning at a depth of three inches. Planting in cold soil only increases the probability that the seedlings will pick up diseases.
Plants set out at the correct time will grow rapidly and quickly surpass plants set out weeks earlier, but they still need protection from frosty nights. April may also bring warm, drying winds that rapidly change the soil from wet to dry. Young plants will stress if the soil becomes too dry, so monitor the soil moisture in different parts of your garden.
Water seedlings well when planting; rewet when the soil dries down to one inch. Water established shrubs and trees to a depth of three feet when the top six to 12 inches feel dry. Water lawns so that the top 12 inches of soil is moist. Reapply water when the soil dries down to three inches.
At the beginning of April, you can plant flowering annuals like alyssum, calendula, forget-me-nots, dianthus and pansies. It's also a good time to sow seeds of beets, carrots, chard, chives, endive, parsley, radishes and turnips. Perennials such as delphinium, daisy, penstemon and lavender may be planted now. And if you haven't already done so, get your summer bulbs (amaryllis, caladium, dahlias, gladiolas, and tuberous begonias) in the ground.
When the soil warms sufficiently, begin planting seedlings of tomato, pepper, eggplant, basil, sage and thyme. You can plant beans and corn directly from seed. At the end of the month, you can sow seeds for cosmos, marigold, zinnia and sunflower, but be prepared to protect from frost. It is usually better to wait until May to plant these heat-loving annuals.
Maintenance chores can keep a gardener busy in April. Lawns need mowing, fertilizing and aeration to keep them healthy and extend their lives.
Pull weeds as soon as they appear. Don't let them become too large or set seed.
Fertilize container plants with a diluted solution every two to three weeks, or use a slow-release dry formulation.
Cut off the spent blooms on spring bulbs but leave the foliage to mature naturally. The foliage feeds the bulb for next year's bloom.
Propagate favorite perennials and shrubs this month by planting cuttings taken from the tender growing tips.
Pinch back the growing tips on annuals and perennials to promote bushiness. Pinch back chrysanthemums to 12 inches and they'll produce more flowers in the fall.
Harvest fall and winter plantings of spinach, peas, fava beans, green onions, broccoli, lettuce, root vegetables, chard and parsley.
After the soil warms, spread organic mulch around trees and shrubs to slow down moisture loss. Be careful to keep the mulch away from the trunks. Don't mulch vegetables until the weather is warm every day, which could be this month or not until June.
Patrol for snails and slugs as well as for cutworms in newly seeded areas. Aphids have already been spotted locally on the fresh new growth of roses, so watch for them. Often a strong blast of water from the hose will knock them off.
Check your irrigation system to be sure that plants are getting the necessary water and that there are no leaks or broken emitters.