May in the Contra Costa Garden
May Garden To Dos
General Garden Care
- Check irrigation: unclog heads, make sure coverage hasn’t changed - repair as required. Change the time on irrigation clocks to water in the early morning. Deep soak trees.
- Control emerging weeds: hand pick, hoe, pour boiling water over them (carefully) or spray with a fatty acid-derived herbicide such as Safer weed and grass killer.
- Renew mulch. To stop weeds and keep moisture levels consistent, mulches need to be 3” thick. Keep mulch pulled away from the trunks & root crowns of woody plants.
- Solarize soil in full sun areas where weeds went to seed last year.
- Aerate lawns, fertilize warm season grasses if not growing rapidly. Mow frequently, leaving grass as tall as you and your mower can stand.
- Remove lawns to save water and resources.
Fruits & Vegetables
- Thin fruit.
- Stake or cage tomatoes that were planted last month.
- Check soil temperature before planting various summer crops. Soil thermometers are available from various suppliers.
- Plant seeds of beans, corn, melons and okra once soil temperatures are at least 65°F (18.3°C). Successive planting of beans and corn will extend your harvest.
- Plant seedlings of tomato, eggplant, peppers, squash when soil is warm enough.
- Plant herbs in full sun with good drainage: basil, chives, oregano, parsley, rosemary, sage, thyme, cilantro, marjoram, borage. These do well in containers.
Flowers & Landscaping
- Cut back the foliage of ornamental grasses before new growth emerges.
- Remove foliage of spring blooming bulbs only after it has turned brown.
- Apply iron chelate to acid-loving plants if chlorotic: citrus, azaleas, camellias, rhododendrons, Pieris. Acidic soil amendments will help lower soil pH.
- Purchase perennials and interesting annuals if you have enough water to keep them going. Great local sources abound!
Garden Pests & Diseases
- Earwigs: Trap by placing moistened, tightly rolled newspaper or corrugated cardboard in the garden in the evening. In the morning, dispose of the paper and trapped insects. Another method of control is a covered container such as a small margarine tub with holes cut halfway up the sides. Pour in about an inch of soy sauce and a thin layer of vegetable oil in the container. Empty as needed. Remember, they eat aphids and other pests.
- Fireblight: This bacterial pest affects ornamentals in the rose family: Pyracantha, Cotoneaster, flowering pear, crabapple, mountain ash, hawthorne and fruit trees (apple, pear and quince). Prune to remove affected branches.
- Fruit tree borers: Paint trunks of fruit trees with 50/50 mix of white latex paint and water. The paint can often be picked up for free at the hazardous waste recycling center at Central Sanitary.
- Gophers: Ultrasonic devices, chewing gum, hair, urine, kitty litter and all the other “great” home remedies are ineffective.
- Snails & Slugs: Control with hand-picking, yeast traps or iron phosphate baits.
- Snapdragon rust: Forms unsightly dark brown or rust colored pustules or blisters on the leaves and stems. Keep your plants growing vigorously by watering and feeding properly.
- Other pests common in May include aphids, scale, powdery mildew, and coyotes. See below for UC IPM Pest Note links.
For More Information
Local Weather Information
Linked data is from the California Irrigation Management Information System (CIMIS) weather stations. Visit CIMIS web site.
Contra Costa County Stations
USDA zones range from 8-9B
Sunset zones range from 7-17
Average max. temp. 75°F, 24°C
Average min. temp. 45°F, 7.2°C
Average rainfall .22", .59 cm.
May 1st is Beltane, the cross quarter day, halfway between spring solstice and summer equinox.
"By the time one is eighty, it is said, there is no longer a tug of war in the garden with the May flowers hauling like mad against the claims of the other months. All is at last in balance and all is serene. The gardener is usually dead, of course."
- Henry Mitchell, The Essential Earthman, 1981