By Susanne von Rosenberg, UC Master Gardener of Napa County
It's a wonderful time of year to be in the garden. Flowers are everywhere and cool-season vegetables are still yielding their bounty. There are too many shades of green to count, and the weather is nearly perfect for enjoying the outdoors. Now is also the time to take action to keep your garden happy and thriving into summer.
The soil has warmed up, so it's a great time to plant warm-season vegetable starts such as tomatoes, peppers, eggplants, melons and cucumbers. You can grow beans, squash, melons, cucumbers and corn from seed. The ideal time to plant melons and squash from seed is mid-May. These plants really prefer warm soil. Wait until the soil warms later in the month to mulch your vegetables. Flowers that you can plant directly from seed now include marigolds, cosmos, zinnias, nasturtiums and sunflowers. Keep the seed bed moist until the seedlings emerge and protect them from insects and birds, if needed.
It also time to replenish the mulch around your trees and perennial shrubs. For trees, extend the mulch one foot past the drip line and keep it at least three inches away from the trunk to avoid fungal diseases. Compost or bark chips make great mulch for trees and other perennials. If you have deciduous fruit trees, thin the fruit. It's best to remove the excess fruit before it reaches the size of a nickel. Your goal is to have enough room between fruits so they won't touch when mature, and of course you also want to make sure that branches aren't overloaded when the fruit is ripe.
We've had to water the garden already this year, but now water demand will increase rapidly. Your plants need about three times as much water from late June through late July as they do in April. Check your irrigation system to make sure all the emitters are working properly. If you're using a sprinkler, the next time you water set out a few cups or soup cans randomly distributed in the irrigated area. That will allow you to see how much water your sprinkler is actually delivering, and if you're getting even coverage.
How much do you need to water? If the soil is dry two inches down in your vegetable bed, then it's time to water. In other areas, depending on the types of plants, you can let the soil dry to a depth of three to six inches between watering. For trees, watch the local hillsides. When they turn golden (when the grasses dry out), it's time to water. Dry grasses mean the soil has dried to a depth of six inches or so.
If you have sandy soil, one inch of water will penetrate about one foot. In clay soil, it will penetrate about six inches. For trees, water should penetrate to a depth of at least two feet (80 percent of a tree's roots are in the top two feet), and no more than three feet. Master Gardeners recommend applying three to four inches of water (depending on your soil) to trees when you water. Then water them again every four to six weeks. Remember to check your soil and consider the temperature, wind and hours of daylight; adjust your watering as needed.
Drought-tolerant native plants do not need irrigation yet. Some of them will appreciate light irrigation in summer. It's important to know which native plants welcome a little water and which ones don't. You can kill a Fremontia (flannel bush) more than three years old by watering it in summer. Our native oaks also only need summer water during drought years.
May is a good time to fertilize annual plants, flowering shrubs, fruit trees and vegetables. Roses should be fertilized after their first big bloom. Place the fertilizer in an area that will receive water. Fertilizer needs moisture to break down and become available to plants. Most trees and shrubs do not need fertilizer unless they are showing signs of a deficiency.
Insects are thriving along with our plants. Insects reproduce more rapidly in warm weather. Keep an eye out for pesky ones. If you can prevent the first generation from reproducing (or at least cut way down on how many make it that far), then you can likely keep numbers down all summer. Also continue to pick slugs and snails (or use a non-toxic bait) and control earwigs and aphids.
Be vigilant about weeding as well. The smaller weeds are, the easier it is to remove them and the less damage uprooting them will cause to the roots of nearby plants. The most important thing is to keep weeds from setting seeds. If you remove weeds when they are flowering, either put the flowers into your yard waste or chop them up. Some weeds can form seeds if they have flowered before you remove them.
The UC Master Gardeners of Napa County are volunteers who provide University of California research-based information on home gardening. To find out more about home gardening or upcoming programs, visit the Master Gardener website (napamg.ucanr.edu). Our office is temporarily closed but we are answering questions remotely and by email. Send your gardening questions to mastergardeners@countyofnapa.org or leave a phone message at 707-253-4143 and a Master Gardener will respond shortly.
Flowers in the spring make me happy. When my grandmother was alive, she often had cut flowers from her garden on the piano, arranged in a vase that belonged to my great-grandmother. I have wanted to recreate the serenity of that picture in my mind. So when I get seed magazines early in February, I dutifully look over the vegetables and herbs that make up the majority of my garden, but it's the flower varieties that are my true delight.
The dictionary defines an ornamental as a plant grown for its beauty rather than for use. But ornamental flowers do have an important use. They attract pollinators. Ornamental plants and flowers, especially native plants, have evolved over time with the pollinators that visit them as they transfer pollen from one flower to another. And, of course, the pollinators get energizing nectar at the same time.
So while my husband may consider my ornamental plants an indulgence, I justify my effort to help them grow and succeed since they serve a critical purpose. I even tuck the occasional ornamental plant among my edibles.
Ornamentals thrive in the same conditions that most vegetables need. They like loamy soil, sufficient water to keep the soil from drying out, and sun for at least six hours a day. Good drainage helps—a sloped site is great—and they welcome a yearly application of compost. Some ornamentals need staking or trellising to support their growth.
So-called native ornamentals are the ones that thrive in our Mediterranean-type climate of rainy winters and dry summers. They may have originated in western Africa, Australia or around the Mediterranean Sea. They have had a long time to interact with pollinators such as bees, butterflies, hummingbirds, moths or bats. This long association creates the symbiosis that secures the continued presence of that species. The California Native Plant Society has a good selection of these native ornamental plants and flowers and conducts a plant sale twice a year in Napa.
One of my favorite native plants that blooms as early as February and continues through summer is the Ceanothus ‘Dark Star' (California wild lilac). It is an evergreen perennial shrub. This plant is extremely drought tolerant and thrives with little watering after the first year. This species can be seen on the east side of Highway 29 south of Trancas Street in Napa. The blooms are blue and blue-purple, and some varieties reach eight feet tall by eight feet wide.
Another favorite native of mine is Ribes sanguineum (red-flowering currant), which is a deciduous perennial shrub. It ranges from 5 to 12 feet tall and wide. It grows well in partial to deep shade, and it tolerates clay soil. It blooms from January to March, providing food for bees early in the year. Birds are attracted to the blue-black berries in the fall. The flowers are deep pink to red, and the leaves resemble maple leaves.
A third ornamental that I enjoy is the dahlia in its many varieties. It is a perennial grown from tuberous roots. About a month before planting dahlia tubers in spring, add a generous amount of compost to the bed. Dahlias are wonderfully diverse. Blooms may be single or double and in shapes such as pompom, ball and orchid. Height ranges from one foot to more than seven feet, with blossoms ranging from two to twelve inches across and un all colors but true blue. Dahlias prefer full sun and do best with staking or caging and moderate watering. Their strong stems can hold the flowers erect even after cutting.
Zinnias are another long-time favorite of mine. They have colorful round flowers; the “elegans” species is the most common. Zinnias may be annuals or perennials. They like full sun and need regular watering. You can grow them from seed or nursery starts, but they don't benefit from being planted too early. The plants bloom until October or the first frost. They are prone to powdery mildew if subjected to cool, foggy or damp weather. These warm-weather plants have strong stems and long-lasting blooms. Cut flowers can last up to a week.
Now, where did I put my great grandmother's vase last fall?
Workshop: The U.C. Master Gardeners of Napa County will host a workshop on “Garden Basics 2: Ornamentals & Flowers” on SATURDAY, April 22, from 9 a.m. to 2 p.m., at the University of California Cooperative Extension office, 1710 Soscol Avenue, Napa. The workshop will showcase dozens of blooming ornamentals. Tips for grouping plants with similar growing requirements, good selections for our Mediterranean climate, flowers for pollinators, growing flowers from seed, best-performing perennials for Napa County and the use of structural plants to define your garden will complete the morning discussion. In the afternoon, visit a local garden that features ornamentals. Bring a sack lunch and please wear walking shoes and clothes appropriate for outdoors.Online registration (credit card only); Mail-in registration (check only or drop off cash payment)
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.edu/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.