By Karen Chang, U. C. Master Gardener
May should indeed be a month to enjoy in the Napa Valley this year. April brought moderate temperatures and showers, which allowed blossoms to linger and forestalled the use of irrigation for a bit. Iris and roses should be at their best now, along with the last of the wildflowers and spring blooms.
Just about anything can be planted now that the threat of frost is past. Itís time to think about watering and pay attention to the active insects as we enter the warm, dry season.
Olive Alert: All gardeners with olive trees should take steps to combat the olive fruit fly, a pest that can devastate an olive crop by laying its eggs in the fruit. Untreated residential trees can provide a virtually endless supply of olive flies. The flies move easily from landscape trees to infest commercial groves.
If you do not plan to harvest the olives from your trees, act now to prevent fruit formation. Spray trees with a strong blast of water to knock off the blossoms. Or apply a growth regulator, such as Florel or Fruit Stop, available at nurseries. Remove any fruit that develops after applying the growth regulator. At harvest time, collect and destroy any fruit on the tree or on the ground, or bury it at least four inches deep.
If you plan to harvest your olives, contact the Napa County agricultural commissionerís office at 707-253-4357 for advice about effective sprays and traps. Fruit harvested early, when still hard and green, will have less fruit fly damage.
Planting: Sow annual flower seeds directly in the soil or set out nursery six-packs. Consider cosmos, dahlias, lobelia, marigolds, nasturtiums, nicotiana, petunia, phlox, salvia, sunflowers, sweet alyssum and zinnias.
Long-blooming perennials provide a good source of cut flowers. Try altroemeria, coreopsis, gaillardia, gloriosa daisy, lavender, purple coneflower, scabiosa, Shasta daisy and yarrow.
Sow these vegetable seeds directly: beans, carrots, corn, cucumbers, endive, lettuce, lima beans, melons, peas, pumpkins, radish, summer squash, Swiss chard and turnips. If plants need support systems, install them at planting time. Hammering posts in later could damage root systems.
Plant seedlings of basil, eggplant, peppers and tomatoes.
Fresh-picked herbs add zest to recipes. Good choices to plant now are basil, chives, cilantro, oregano, parsley, rosemary, sage and thyme. Not sure how to care for herbs? Napa County Master Gardeners are hosting a free public workshop on gardening with herbs on May 7 in Napa and May 21 in St Helena. Call 707-253-4221 for details.v
Spring-blooming shrubs such as azaleas, rhododendrons and camellias may be planted in May. You can also plant tender shrubs like bougainvillea, fuchsia, hibiscus, lantana and mandevilla.
Soil management: Apply mulch now to suppress weeds, retain moisture and protect the soil and surface roots from the hot summer sun. Use at least two inches of organic material around shrubs and trees, extending to a foot beyond the drip line and to within six inches of the trunk. Wait until the soil is well warmed before mulching around summer vegetables.
Check your drip-irrigation system to make sure itís operating properly. Clean filters, check emitters and spray heads, inspect lines for leaks, and adjust the automatic controller as the weather gets warmer and drier. Also open the end caps and flush out the lines after making repairs.
Monitor your soil moisture, especially if we have some windy days and no more rain. Probe to a depth of three to six inches. If the soil is dry and crumbly, itís time to start irrigation. Use the following rule of thumb: one inch of water applied to the surface will replace what the plants use a foot deep. Apply three inches before the heat sets in and then every four to six weeks during the summer.
Smaller shrubs, flower beds and vegetable beds should get a good soaking of one to three inches if the soil is dry.
Maintenance: Prune spring-blooming shrubs and vines when they have finished flowering.
Dead-head (remove dead flowers) from flowering shrubs and plants so the plant directs energy to producing new growth rather than seed.
When spring-blooming bulb foliage has turned yellow, cut it off, or wait until it turns brown and pull it off. If bulbs are crowded and didnít bloom well, mark them to divide in summer.
In most years, apple, apricot, nectarine, peach, plum, Asian and European pear trees need fruit thinning so that the remaining fruit can develop to a good size. Gently twist off fruit when it is about one-half to three-quarters inch in diameter, leaving about six inches between each fruit. Excess fruit can also break branches.
Watch for aphids, earwigs, snails and slugs.
Keep weeds in check by pulling seedlings when they are small and easily removed. Try not to let weeds go to seed.
Harvest: Enjoy the vegetables from your winter planting: bok choy, cabbage, chard, cauliflower, fava beans, green onions, lettuce, parsley, peas, radish, beets and other root vegetables.
Napa County Master Gardeners present "Down The Garden Path" on Sunday, June 12, from 10 a.m. to 4 p.m. This self-guided tour of six unique private gardens owned, designed and maintained by Master Gardeners will give home gardeners many useful ideas. Tickets are $20 in advance, $25 on the day of the event. For information call 707-942-1446; or visit the Tour section of our website.