We in the Napa Valley depend on the winter rains to fuel and sustain the growth of our home gardens, vineyards and landscape. Downtown Napa has received less than 3.6" of rainfall since July 1, 2013, well below the average of 15.7" from past years.
While water conservation has long been an integral part of planning and maintenance of home gardens and landscapes, it is now an absolute imperative. Drip irrigation can reduce water usage by as much as 50 percent. Remove weeds that compete with your plants for water. Do everything you can to slow evaporation of precious water by mulching, providing wind breaks, and planting in blocks to provide shade for roots. Step up your pest control efforts as water stressed plants are more susceptible to infestation and disease. To aid the home gardener, UC Davis, UCCE, and Master Gardener groups are compiling and publishing research based information that can assist home gardeners in making informed choices during this period of drought.
Below are some ideas gathered from "Keeping Plantings Alive under Drought or Water Restrictions" by Janet Hartin and Ben Faber, published through UC Cooperative Extension, ANR:
Plants will show signs of stress during drought. Plants should be checked regularly for characteristic symptoms and watered in the early stage of water deficit to prevent irreversible damage. It is suggested to check plants in the afternoon when symptoms will be most evident.
- wilting or drooping leaves that do not return to normal by evening
- curled or chlorotic (yellow) leaves
- new leaves that are smaller than normal
- lawn grasses that retain a footprint for several minutes
One or two deep irrigations with a garden hose several weeks apart in spring and summer will often keep these valued plants alive through summer, especially if roots are relatively deep. Although mature trees can often survive one season with only one or two deep waterings during the spring and summer, two seasons without enough water can result in severe drought stress and even death. Drought-stressed trees can be more prone to damage from diseases and insects.
Fruit and Nut Trees
To produce a good crop, deciduous fruit and nut trees need adequate water in their root zones continuously from bloom until harvest. Citrus trees need adequate soil moisture during spring to set fruit and steady water in summer and fall to produce acceptable size, numbers, and quality of fruit. However, fruit and nut trees can be kept alive with a few early-season water applications, but they may not set much fruit.
As a rule of thumb, water is most critical during the first few weeks of development, immediately after transplanting, and during flowering and fruit production. Tomatoes, beans, and root crops such as carrots require regular watering and are not tolerant to long, dry periods. Viney vegetables such as squash and zucchini can be kept alive with a few waterings once or twice a week through the season.
The full article can be found: Keeping Plantings Alive under Drought or Water Restrictions
Additional sources of information are available through the Drought Tips page at the UC Master Gardeners of Napa County website.
Growing guidelines for radishes
Dig the soil to a depth of 6 inches for quick-growing radishes and up to 2 feet for large, sharper-tasting, slower-growing winter types. Space seeds ½ inch deep and 1 inch apart; firm the soil and water gently. Thin seedlings to 2 inches apart, 3 to 6 inches for the larger winter types and mulch to keep down weeds. For quick growth and the best flavor, water regularly. Make weekly spring sowings as soon as you can work the soil (4 to 6 weeks before the last expected frost) until early summer; start again in late summer. Sow winter radishes in midsummer for a fall harvest.
Spring radishes should be planted from as early as the soil can be worked until mid-spring. Make successive plantings of short rows every 10 to 14 days. Plant in spaces between slow-maturing vegetables (such as broccoli and brussels sprouts) or in areas that will be used later for warm-season crops (peppers, tomatoes and squash). Spring radishes also can be planted in late winter in a protected cold frame, window box or container in the house or on the patio. Later-maturing varieties of radishes (Icicle or French Breakfast ) usually withstand heat better than the early maturing varieties and are recommended for late-spring planting for summer harvest. Winter radishes require a much longer time to mature than spring radishes and are planted at the same time as late turnips (usually midsummer to late summer).
Spacing & Depth - Sow seed 1/4 to 1/2 inch deep. Thin spring varieties to 1/2 to 1 inch between plants. Winter radishes must be thinned to 2 to 4 inches, or even farther apart to allow for proper development of their larger roots. On beds, radishes may be broadcast lightly and thinned to stand 2 to 3 inches apart in all directions.
Care - Radishes grow well in almost any soil that is prepared well, is fertilized before planting and has adequate moisture maintained. Slow development makes radishes hot in taste and woody in texture.
Radishes mature rapidly under favorable conditions and should be checked often for approaching maturity. Harvest should begin as soon as roots reach edible size and should be completed quickly, before heat, pithiness or seedstalks can begin to develop.
Harvesting - Pull radishes when they are of usable size (usually staring when roots are less than 1 inch in diameter) and relatively young. Radishes remain in edible condition for only a short time before they become pithy (spongy) and hot. Proper thinning focuses the harvest and avoids disappointing stragglers that have taken too long to develop.
Winter varieties mature more slowly and should be harvested at considerably larger size. Once they reach maturity, they maintain high quality for a fairly long time in the garden, especially in cool fall weather. Size continues to increase under favorable fall conditions. Daikon or Chinese radish, can achieve particularly large size and still maintain excellent quality. Winter radishes can be pulled before the ground freezes and stored in moist cold storage for up to several months.
Questions & Answers
Q. What causes my radishes to crack and split?
A. The radishes are too old. Pull them when they are younger and smaller. A flush of moisture after a period of relative dryness also may cause mature roots to burst and split. Try to avoid uneven moisture availability.
Q. Why do my radishes grow all tops with no root development?
A. There may be several reasons: seed planted too thickly and plants not thinned (though some roots along the outside of the row usually develop fairly well even under extreme crowding), weather too hot for the spring varieties that do best in cool temperatures (planted too late or unseasonable weather) and too much shade (must be really severe to completely discourage root enlargement).
Q. What causes my radishes to be too "hot"?
A. The "hotness" of radishes results from the length of time they have grown rather than from their size. The radishes either grew too slowly or are too old.
Selection & Storage
Summer Radish - Radishes have often been dismissed as decoration and garnish. They are actually members of the cruciferous vegetable family so eat the greens. Because they vary in keeping quality, radishes are classified as winter or summer. Summer radishes are the small ones of bold red, pink, purple, white or red and white. They may be globe-shaped or elongated, fiery hot or mild. Harvest summer radishes when they are small and tender for optimal flavor. Oversize summer radishes can become tough, woody, hallow and strong in flavor. To check a large radish squeeze gently, if it yields to pressure it is likely to be fibrous. These will do well in the compost heap.
Winter Radish - Harvest winter radishes when they are large and mature. Winter radishes may be white, black or green. Black radishes have a pungent flavor and should be used sparingly. Remove greens and roots before storing black radishes. Chinese radishes, round and fat, are milder in flavor. Remove greens before storing; remove roots just before preparing. The word daikon means "great root" in Japanese. In cool weather, daikon growth is quick and steady. The fully mature daikon can grow up to about 18 inches long and weighs 5 or 6 pounds. There are several varieties. Some are thin and long, while others are short and round. All radish greens are edible.
Save the young thinnings of both summer and winter radishes. They are delicious with tops and bottoms intact. Both summer and winter radishes store well in the refrigerator once the tops have been removed. The radish leaves cause moisture and nutrient loss during storage. Store greens separately for 2-3 days. Refrigerate radishes wrapped in plastic bags for 5 to 7 days. Winter radish varieties can be stored for up to two weeks in the refrigerator.
Nutritional Value & Health Benefits
The popular red globe radish is low in calories with an abundance of flavor and crunch. A 1/2 cup serving (about 12 medium) of sliced radishes provides a goodly amount of potassium, vitamin C, folate and fiber. Winter radishes such as daikons are similar in nutrients.
Nutrition Facts (1/2 cup fresh sliced raw red globes)
Protein 0.35 grams
Carbohydrates 2.0 grams
Dietary Fiber 1 gram
Potassium 134.56 mg
Folate 15.66 mcg
from Spill the Beans!
Thanks to UC Master Gardener John Chwistek for compiling these plant profiles. Plants featured are suited to areas found in Napa County. Following are recent plants he has highlighted.
By John Chwistek
Common name: Fern bush
Botanical name: Chamaebatiaria millefolium
Classification: Deciduous shrub, semi-evergreen in warm climates Sunset zones: 1-3, 7, 14-21
Native: Western U.S. (3,000 - 7,000 ft. mountain slopes) Height: 6-7 feet
Spread: 6-7 feet
Flower color: White 1- 4 inch clusters
Notes: Needs good drainage. Foliage is fragrant, fernlike, scaly and sticky. Flowers attract butterflies and bees. Attractive fall color. Fruits are four or five leathery follicles per flower.
Sources: Sunset Western Garden Book, Colorado State University Cooperative Extension, Trees and Shrubs of California
Common name: Flat-leaf summer holly
Botanical name: Comarostaphylis diversifolia var. planifolia
Classification: Evergreen shrub
Sunset Zones: 7-9, 14-24
Native: Southern Channel Islands
Height: 8 - 12 feet
Spread: 6 - 8 feet
Flower Color: White
Exposure: Full sun to partial shade; full sun in cooler climates
Notes: Any well-drained soil, moderate water
Sources: Sunset Western Garden Book, Tree of Life Nursery,
UC Berkeley Botanical Garden
Botanical name: Epilobium canum ‘Hurricane Point’
Classification: Shrubby perennial
Hardiness: USDA zone 8a - 10b
Native: Western U.S. and northern Mexico
Height: 1 foot
Spread: 2 feet
Flower Color: Orange-red
Bloom: July - October
Notes: Prefers occasional water, compact plant, hummingbird plant.
After the first year, cut back 1-2” in late fall or winter
Sources: Sunset Western Garden Book, UC Santa Cruz Arboretum,
Yerba Buena Nursery
UC Master Gardeners of Napa County answer garden questions at our Help Desk on Mondays, Wednesdays, and Fridays from 9:00 a.m. - 12 noon. Free advice is given for growing conditions in Napa County and there are three ways to contact us:
Drop-in: UC Cooperative Extension-Napa County, 1710 Soscol Avenue, Ste 4
The Help Desk fields a range of questions. Thanks to UC Master Gardener Monica Finigan for writing about the following recent inquiries to the Help Desk.
Strange-looking Strawberries: Client called about the strange-looking strawberries growing on his strawberry plant. The strawberries looked “hairy.” They had small leaves sprouting around the seeds on the fruit. The strawberry plants had been growing in a wine barrel for eight years. This strange appearance is called a “phylloid.” Although there are several possible causes, the recommendation was to destroy the plants and plant new strawberries in new soil and in a different location. Strawberries are subject to several soil borne diseases and should be replaced every three years (or sooner if needed) and planted in a new location.
Meyer Lemon: Client called to ask why her Meyer lemon had not borne fruit. Her tree is four feet tall. She did not know the age as she “inherited” the tree from someone. She also indicated that it did not look good when she received it, so she pruned it during the summer. There are many possible reasons for its failure to bear. She may have pruned off the buds or the tree might not have had buds due to insufficient watering, lack of nutrients, not enough exposure to sunlight, or because it is a young tree. Citrus bear little or no fruit during their first three-to-four years.
Yellow leaves on Meyer Lemon: Client called regarding yellow leaves on a Meyer Lemon tree. Patterns of yellowing on the leaves can be an indication of a nutrient deficiency. The most common nutrient deficiency in lemons is a lack of nitrogen. The most important time to apply fertilizer is late winter or early spring, but application can also be divided into three times during the year for lemons. Fertilizer needs to be scattered over the entire root area of the tree, which extends one to two feet beyond the drip line. Consult the application directions on the fertilizer package.
Mysterious Orange Growth in Mulch: Client called to ask about a bright orange “something” in his mulch. Should he be worried about it? He was told that it was probably a fungus or slime mold. Most fungi are decomposers, and he should not be concerned, but he should make sure that a child or pet doesn’t eat it. He later called back to say he had looked more closely and the orange growth appeared to be a cluster of small mushrooms.
Flies in Walnut Husks: Client reported that there was an infestation of flies in the walnut husks of his tree, and the husks were stained black. Walnut husk flies primarily damage the husks and the walnut shell. Generally, the flies do not damage the nutmeats. The damaged husks can be placed in a damp burlap bag for a few days before attempting to remove the hull. Infested husks should be disposed of in a tightly sealed bag. Good sanitation can help reduce the number of husk flies overwintering nearby. Remove and dispose of damaged nuts as soon as possible. Spread a tarp under the tree from July through August to prevent the maggots from entering the soil to pupate. For severe infestations, spinosad can be sprayed on a 7-to-14 day interval beginning in July until within one month of harvest. Adding a bait to the spray would eliminate the need to cover the entire tree since the flies would be attracted to the bait and would eat the spray. The home gardener might want to consider using molasses as the bait (4-to-6 tablespoons per gallon of water) and always follow label instructions.
Olive Fruit Fly: Client requested information on preventing a re-infestation of olive fruit fly on her trees. Her neighbor leaves the olives on his tree every year. She also wanted to know how to dispose of the infected fruit. Management of this problem will be a challenge with an uncooperative neighbor. Infected fruit can either be disposed of at the landfill or buried in the ground, at least four inches below the surface. In the following year, a combination of bait traps to reduce the population and application of barrier film sprays on the trees should be considered. The barrier film should be applied as the flies begin to attack the fruit in late summer. See Pest Note 74112 for more information.
Growing Crocus: Client wanted to know if crocus bulbs need to be pre-chilled before planting and whether crocus bloomed for only one day. Bulbs do not need to be pre-chilled in the SF Bay area. Crocuses bloom for an extended period of time, not just for one day. They do well in this area, since crocuses originated in the Mediterranean area.
As gardeners we often love to push the envelope for our planting zones or desire a plant that may not be well suited to our climate. Some of the popular subtropical plants we love to grow that are marginal in our climate include citrus, avocados and Bougainvilleas. In Napa County, depending on your gardens microclimate, you may be able to grow many plants native to subtropical climates. But these plants need frost protection when temperatures dip into the 30 - 20 degree F range. Some of these plants will tolerate and recover from short exposure to mild frost with only minor frost damage but prolonged frost for several hours or days in a row may kill some plants. Below are some tips for frost protection and for management after frost damage has occurred.
HEALTHY GARDEN TIPS
Web site: http://cenapa.ucdavis.edu
University of California Cooperative Extension – Napa County
Freeze Protection Simplified
By Dean Donaldson, Farm Advisor Emeritus
1. Make sure your plants are well watered before frost occurs. Well hydrated plants will tolerate colder tempertures and the wet soil will hold some heat.
2. Throw a blanket or sheet, etc. over the plant. Remove when sunny. Recover each night.
‘Engineer’ types can build a cage (OK, but not necessary). Expect burnt leaves and twigs
but plant will be OK. Lightweight fabric or woven cover is superior to plastic.
3. Citrus – fruits will be damaged. Damaged fruit will dehydrate inside. Within a few days
following a frost, fruit should be picked and squeezed. You can freeze juice for later use.
Do not prune until re-growth is visible next spring.
4. Supplemental heat from small wattage bulbs can help reduce frost damage. Use 15
watt, 20-25 watt (outdoor-type) bulb to avoid leaf burn from light bulbs. Outdoor
Christmas lights (larger, old-fashioned) work well if +15 watts (smaller, LED Christmas
lights do not release heat). Place bulb in lower tree canopy and keep lit all night until
temperature is above 32° F. Be sure to also use outdoor-type extension cord and fixture.
5. Do not prune damaged parts until after plants re-grow, usually in April or May.
Frost Protection and best varieties of Citrus to grow in Napa County:
Varieties of citrus with lower heat requirements do best in Napa County. Although frosts are infrequent in the winters near San Francisco and in the thermal belts of many valleys in this region, low-lying inland areas can have temperatures below freezing. Citrus variety, site selection and winter protection are important factors for success in growing citrus in Napa County.
Cold-hardiness depends on the type of citrus grown. Early ripening varieties in our freeze-prone area can facilitate harvesting before the danger of frost. Citron and lime trees are the most tender types, sweet orange and grapefruit varieties are intermediate; and Satsuma mandarins, Meyer lemons and kumquats are the most cold-hardy.
Among sweet oranges Robertson Navel, Skaggs Bonanza, and Washington Navel can be harvested as early as December in Napa County.
Valencia oranges ripen later, but some newer varieties are sold as "improved" Valencias, which ripen earlier, set fruit inside the canopy (more protected), and boast bigger fruit. Three sold under separate names are Delta, Midknight, and Rhode Red.
If blood oranges suit your fancy, Moro is the only choice for color and flavor recommended for Napa County.
Early ripening Clementine Mandarins have excellent flavor. There are many selections, but those that require a pollinizer for good production have seedy fruit. Dancy and Kinnow mandarins, Orlando tangelo, and Valencia orange are commonly used as pollinizers. If you have room for only one tree, choose a variety that does not require a pollinizer. Clementine has produced many hybrids, such as Page, Fairchild, Ambersweet, Lee, Nova, and Robinson. Satsuma Mandarins are the most cold-hardy citrus and the earliest bearer. They can be grown in areas normally too cold for citrus. Ripening occurs before dangerous frost occur, and the foliage survives temperatures to about 22F degrees. Dobashi Beni, Okitsu Wase and Owari are selections that thrive in cooler regions.
The University of California Division of Agriculture & Natural Resources (ANR) prohibits discrimination or harassment of any person in any of its programs or activities (Complete nondiscrimination policy statement can be found at http://ucanr.org/sites/anrstaff/files/107778.doc ). Inquiries may be directed to Linda Marie Manton, Affirmative Action Contact, University of California, Davis, Agriculture and Natural Resources, One Shields Avenue, Davis, CA 95616, (530) 752-0495.