UC Master Gardeners, Santa Clara County, CA
University of California
UC Master Gardeners, Santa Clara County, CA

May Tips

Monthly tips are categorized by: To-Dos, What to Plant, or Pests and Diseases. Scroll through the list to see items in each category.

1. To-do

  • Bee Swarms -

    Bees are very active in warm weather. There is simply so much pollen and nectar to collect! Sometimes, a bee colony may swarm. If you see a swarm, don’t panic. As in any other time when working around bees, remain calm, move gently, and give them their space. Bees generally swarm when they are looking for a new home. Swarming bees are loaded with food and are not interested in stinging people. Contact the Bee Guild to have swarms removed.

    - May, June
  • Composting -

    Composting is a good way to repurpose yard and kitchen waste, and it provides a free method to feed plants and improve soil structure. If you are unsure about how to begin composting, take a look at this simple how-to compost page. You can also go to the UCCE Composting Education Program website to learn more about free two-hour classes offered throughout the county.

    As the weather warms up, compost piles dry out faster. Keep compost piles as damp as a wrung-out sponge to keep organisms alive and working on decomposing yard waste. Turning the pile to incorporate more oxygen also supports life in the compost pile.

    - January, February, March, April, May, June, July, August, September, October, November, December
  • Deadheading -

    Deadheading means removing spent blossoms from your plants. Not all plants need deadheading, but if the flowers stay on the plant and become unattractive (think roses, dahlias, marigolds, coneflowers, geraniums and many more), then consider a little pruning. The technique varies by plant; some spent flowers can be snapped off by hand (dahlias), others are better done with hand pruners (roses), and some can be sheared off all together (lavender). You'll not only make the plant look better, you'll stimulate additional blooming for plants that have a long blooming season.

    - April, May, June, July, August, September
  • Drip Irrigation -

    Low volume drip irrigation systemConsider various forms of irrigation conversion! Irrigation systems, especially drip and micro-sprinklers, have drastically improved over the last few years. For example, there are kits that convert pop-up sprinkler heads to low-flow systems. The conversion kits include a pressure regulator to control changes in pressure and a filter to improve water quality. Water usage is reduced through better water management, control of distribution and less loss from evaporation. Other advantages include :

    - Water is placed more accurately and efficiently in the root zone, it is applied at a slow rate that reduces loss from runoff.
    - Dry soil between plants allows you to work in the garden between irrigating.

    The key to success is watering long enough to supply adequate water to the root zone. Inappropriate watering commonly damages landscape plants. As with any irrigation system, they are efficient only when soil around the plants being irrigated is regularly monitored for proper moisture levels (Reference: UC Pest Note Poor Water Management, Poor Drainage).

    - March, April, May, June, July, August, September
  • Fertilizing Ornamentals During Drought -

    One way to manage plants during drought is to reduce the amount of fertilizer used. While plants need nutrients to survive and be healthy, excess fertilizer promotes additional growth, which then demands more water.

    - May, June, July, August
  • Fruit Tree Sunburn Protection -

    In hot, sunny weather, the bark of fruit trees, especially when they're young, can get sunburned and begin to crack or peel. This allows tree borers and other pests and diseases to enter, which can cause significant damage to the trees. To protect exposed trees, the bark can be painted with white latex paint, mixed 50-50 with water.

    If you have a new fruit tree that hasn't been painted, do it now. And consider other fruit tree trunks if they have significant sun exposure.

    - May
  • Hardening Off Seedlings -

    Seedlings that have been raised in protected conditions, like in greenhouses or indoors, need to be gradually exposed to outdoor conditions for one to two weeks before transplanting. This process is known as “hardening off.”

    To harden off seedlings, first move them outside to a shady, wind-sheltered area for a few hours a day, bringing them inside at night. After a few days of that treatment, place them in the sun for a few hours in the morning or late afternoon and gradually increase the sun exposure. Reduce the frequency of watering, but do not allow the plants to wilt. Do not place seedlings outside on really windy days or when the temperatures are below 45 deg F.

    After a couple of weeks, once the seedlings are used to full sun and can stay outside overnight, they are hardened off and are ready to transplant into the garden.

    - May
  • Irrigation and Graywater -

    As temperatures rise, irrigation becomes more important. Container plants will begin to dry out and need to be checked every few days. Inspect irrigation systems for leaks, clogged drip emitters, misaligned sprinkler heads, and other problems which could waste water. Make sure the water is going to the root zones of the plants.

    Things to consider:

    Use a smart irrigation controller. These help adjust watering based on local conditions. Learn more about smart controllers.

    Collect water from the shower as it heats up and use it to water any plants.

    Use graywater from garage sinks and washing machines to water ornamentals and lawns. UC has a publication titled Use of Graywater in Urban Landscapes in California.

    - April, May, June, July, August
  • Lady Beetle Larva -

    Sevenspotted lady beetle larva eating an aphidWe all know that lady beetles are good for the garden. Make sure you can recognize the larval stage, which resembles tiny alligators, because this life stage eats even more aphids than the adult form. Before spraying pesticides, remember that a low population of aphids can attract more lady beetles, and potentially keep the pest population below a damaging threshold. Read more about Lady Beetles in the UC Pest Note on Convergent Lady Beetles.

    - May
  • Lawn Care -

    If you have a lawn, be sure to water it as early in the morning as possible to avoid evaporation. This also helps reduce fungal diseases by giving grass time to dry out during the day. Poor watering practices are the main reason for dead and dying areas in lawns and a common source of urban runoff.

    Check lawns for weeds such as spurge, burr clover, and whatever happens to invade your neighborhood. When mowing in the summer, set the blade height as high as you are comfortable with—taller grass shades the soil, reducing evaporation and protecting valuable earthworms in the soil. Use the UC Guide to Healthy Lawns to learn more about mowing, irrigating, fertilizing, detaching and aerating. Better yet, take advantage of the County's Lawn Replacement Program!

    - May, June, July, August, September
  • Mulch - a Gardener's Best Friend -

    Mulching around your plants has many benefits. It holds in moisture by reducing evaporation from the soil, keeps weed seeds from being able to germinate, and moderates the temperature of the soil so that it doesn't vary as much with direct sun and changes in air temperature. Mulching can cool the soil for plants like blueberries and it will help hold some heat in for summer vegetables as the air gets cooler.

    Mulch will guard against soil erosion when the rains start. Organic mulch such as wood chips or bark will slowly break down and improve your soil over time.

    It is recommended to keep mulch six inches away from trunks and twelve inches away from buildings. If you are confused about the difference between compost and mulch, then UCCE's Soil Management - Compost versus Mulch Comparison will help.

    Many local tree trimming companies are happy to deliver free wood trimmings that can excellent mulch - just be sure that the trimmings are disease- and palm- and eucalyptus- free. This can be hard to guarantee. Straw (not hay) from the local feed store can also be inexpensive, effective mulch.

    - May, June, July, August, September
  • Pruning Azaleas and Rhododendrons -

    Azaleas and rhododendrons can be pruned as soon as they finish flowering. This is also a good time to fertilize them. Choose an acid-forming fertilizer blended for these particular plants, and be sure to follow the label directions for amounts. Learn more by visiting the Azalea and Rhododendron society websites.

    - April, May
  • Pruning Camelias -

    April and May are the best time to prune camellia. Camellia should be pruned just after flowering and before new vegetative growth gets going. If you prune later in the season, you risk damaging next years blossoms.

    - April, May
  • Pruning Roses to Minimize Disease -

    Midas Touch rose blossomA chemical-free way to keep roses healthy and minimize disease associated with foggy summer mornings is to prune to improve air circulation. Think of your rose bushes as large vases, with open centers. Good air circulation allows the morning dew to dry, and helps prevent rust and powdery mildew. UCCE's Center for Landscape and Urban Horticulture has more info about the Fundamentals of Pruning Roses. The UC Pest Note on Roses has more about general cultural practices and weed control.

    - May, June, July, August
  • Soil Management - Compost vs Mulch -

    Many home gardeners are confused about the terms “compost” and “mulch;” frequently these terms are used interchangeably, but they are not really the same thing. Here is a Comparison of Soil and Mulch from UCCE.

    Amend soil with compost to create soil that will retain water but still drain well enough for roots to have the air and water they need.

    Benefits of compost
    - Forms aggregate particles with clay
    - Creates larger pore spaces for water & air
    - Helps release nutrients from clay so that plant roots can absorb them
    - Supports the soil foodweb by providing nutrients for the organisms
    - Lowers pH somewhat.

    Benefits of mulch
    Mulch does not get worked into the soil. It sits on top of your irrigation system and helps:

    - Control weeds
    - Prevent erosion
    - Preserve soil moisture
    - Keep roots cool and moist

    - March, April, May
  • Tomato Staking -

    It's time to start planning how you will stake your tomatoes. You will want to stake your tomatoes right after you plant your seedlings. Here are the various Tomato Staking Techniques we have tried.

    - March, April, May
  • Watering Hydrophobic Soil -

    Just as a dry sponge repels water, overly dry soil can do the same thing. This dried out soil is called hydrophobic. Hydrophobic soil can waste a lot of water as water drains away from the plant's root zone.

    In pots: learn more about how to re-wet very dry soil on our Watering Hydrophobic Soil page. In the yard: setting sprinklers to run for 5 minutes, waiting for the water to soak in, and then running for a longer time can prevent water loss due to hydrophobic soil.

    - May, June, July, August

2. What to plant

  • Attracting Bees -

    Bees are pollination workhorses, increasing garden production. Many plants will not produce fruit unless flowers are pollinated. Colorful annuals, such as Cosmos, edible African Blue Basil, and Salvias attract bees. You can also allow herbs and other plants to flower to create bee-friendly landscapes.

    The University of California at Davis has a garden dedicated to bees. They're Honey Bee Haven website has more resources, including a list of plants they grow.

    - March, April, May, June, September, October
  • Don't Plant an Invasive Plant -

    According to PlantRight, so-called invasive plants "escape into open landscapes and cause a variety of ecological problems. They displace native plants and wildlife, increase wildfire and flood danger, clog valuable waterways, degrade recreational opportunities, and destroy productive range and timber lands."

    PlantRight has identified the following as invasive in Northern California: Green fountain grass (Pennisetum setaceum), Periwinkle (Vinca major), Pampas grass (Cortaderia selloana), Highway iceplant (Carpobrotus edulis), Mexican feathergrass (Stipa / Nassella tenuissima), Yellow Flag Iris (Iris pseudacrorus), Water Hyacinth (Eichhornia crassipes). For details and recommended alternatives, please consult their Website.

    - April, May, June, July, August, September
  • Growing Peppers -

    As soon as average night time temperatures are above 55° F, peppers can be added to the garden. Before that time, they can be started indoors. Make pepper more productive by planting different varieties closely together. You will get more peppers per square foot because the plants support each other and provide protection from sunburn. Plus, they look lush and beautiful. After planting, it is a good idea to remove flowers and fruit from large-poded plants the first four to six weeks to encourage deeper roots and more foliage. Learn more pepper tips by consulting our Growing Great Peppers and Chiles page.

    - May, June
  • Milkweed -

    Milkweeds are the required host plants for monarch butterflies. Milkweeds provide food for the caterpillar, nectar for the butterfly, and chemical compounds that make the monarchs distasteful to predators. Make sure to choose a variety native to California. The non-native Tropical Milkweed may disrupt monarch migration patterns, because of it's longer growing season, so don't plant it unless you're willing to cut it back to 6" or less from Oct-Feb. Learn more at the UC ANR blog posting on Overwintering Monarchs.

    - May, June
  • Plants to Attract Butterflies -

    Butterfly populations fluctuate in response to climate and habitat conditions. Many have specific host plants on which they feed and breed. Some common plants for attracting butterflies are milkweed, lantana, buddleia, and zinnias. For an extensive list of relationships between specific butterflies and host plants, see Art Shapiro's Butterfly Site at UC Davis.

    - March, April, May, June
  • Summer Vegetables -

    May is a busy month for summer vegetable gardeners.

    Tomatoes: be careful about planting too soon! Tomatoes are best plants when the soil warms to 60ºF. If you're not planting in containers, you may need to wait until the beginning of June.

    Peppers: as soon as average nighttime temperatures are above 55° F, peppers can be added to the garden. Before that time, they can be started indoors. Make pepper more productive by planting different varieties closely together. You will get more peppers per square foot because the plants support each other and provide protection from sunburn. Plus, they look lush and beautiful. After planting, it is a good idea to remove flowers and fruit from large-podded plants the first four to six weeks to encourage deeper roots and more foliage. Learn more pepper tips by consulting our Growing Great Peppers page.

    Squash: both summer and winter squash varieties can be planted now, either by direct seeding or transplants. The designation of winter squash means that they have harder skins and can be stored through the winter, but they're grown in summer.

    - May
  • Tropical Flowers -

    If you have your heart set on tropical and subtropical plants like bougainvillea and hibiscus, planting in May will give them time to get established before the cold weather hits in the fall. Planting them in a protected area such as under eaves may keep you from having to cover them on cold nights.

    - May
  • Vegetable Planting Chart -

    Wondering what vegetables can be planted now? To get the best success—whether planting from seed or transplants—refer to our Santa Clara County Vegetable Planting Chart. It's based on our own garden experiences.

    - February, March, May, June, July, August, November
  • Vegetables Grown In Containers -

    Container grown vegetables can be decorative as well as good to eat. Almost any vegetable can be grown in a container if given the proper care. Eggplant, peppers, tomatoes, lettuce, onions, carrots, cucumbers and herbs do well. One of the biggest problems is that containers dry out very fast and nutrients wash away. Both are solvable. Do not use clay pots, which dry out quickly. Plastic, composite or wooden half-barrels are good, but avoid dark colors that can absorb heat. Vegetables like a roomy container. There must be drainage holes in the bottom but it is not recommended that you put pebbles or broken crockery in the bottom. Use a good commercial potting mix, not planter or planting mix. Group the containers together so they will shade one another. The hot summer sun can heat the soil to unhealthy levels. Water whenever the soil is dry. You can test by digging your fingers into the dirt or using an inexpensive moisture meter. You may have to water more than once a day. A simple drip system is easy to install and will make your container garden almost foolproof. Fertilize every week with a water-soluble fertilizer.

    - May, June

3. Pests and Diseases

  • Carpenter Bees -

    A carpenter bee visits a flower. (Photo by Kathy Keatley Garvey)Female carpenter bees are large, black and shiny. Male carpenter bees are similar in appearance to bumble bees. Both are about an inch long. Males do not sting and females sting only rarely. Carpenter bees are considered beneficial insects because they pollinate many plants and trees. For their nests, they tunnel into unpainted softwoods such as pine, fir and redwood in house or garden structures. Adults over winter in the nests, emerge in the spring, mate, deposit food in the tunnels and lay eggs. The tunnels are sealed with wood pulp and the new adults chew their way out. After the bees emerge, fill the holes with steel wool and wood filler. Apply paint to the surface to prevent re-entry. Further information is available in the UC Pest Note on Carpenter Bees.

    - May, June
  • Codling Moth -

    "Worms" in your apples are actually the larval form of the codling moth. Codling moth larvae can cause a great deal of damage to apples, pears, plums and walnuts by penetrating the fruit and boring into the core.

    Trees should be monitored every week for signs of infestation. Infested fruit should be removed and discarded, to break the coddling moth life cycle. Sanitation is an important non-chemical step in controlling this pest. Make sure to pick up fallen fruit promptly, and pick apples with holes that are still on the tree. This will keep future populations down.

    Pheromone traps can be hung in isolated trees. But if you have just one apple tree don't bother. You will just attract codling moths to your tree.

    Fruit can be bagged for protection, but this is a very labor intensive method. Heavy infestations may require the use of pesticides on the moths, before fruit is affected. For more information, refer to the UC Pest Note on Codling Moths.

    - March, April, May, June, August, September, October, November
  • Earwigs -

    Earwigs are third only to snails and slugs in causing plant damage. While they are beneficial because they eat insects such as aphids, they also feed on soft plants. Earwigs can do quite a lot of damage if there is a high population. They feed at night and hide in moist, tight-fitting places during the day. Trap them by putting out moistened, tightly rolled newspaper or corrugated cardboard in the evening. In the morning dispose of the paper and the 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 and bury up to the holes. Empty as needed. Other control methods are described in the UC Pest Note on Earwigs.

    - May, June
  • Eugenia Psyllid -

    This psyllid has been a real problem in California. New leaves on the infected Eugenia look very much like peach leaf curl. The leaves also may become discolored. Thanks to the diligent work of the entomology researchers in biological insect control at UC Berkeley, a parasitic wasp called Tamarixia was released in Santa Clara County in 1993. The wasp is known to go as far as 45 miles and is found throughout the county. It is essential that no insecticide be used on Eugenia species. The Tamarixia wasp cannot do its job if it's poisoned. For more information see the UC Pest Note on Psyllids.

    - May, June
  • Fire Blight -

    Late spring and early summer are the time fire blight shows itself. Fire blight is a bacterial disease that makes plants look as though they have been damaged by fire. It attacks apples, pear and quince, most often, but can also infect ornamentals, such as toyon and pyracantha. Very often, the growing tip folds over into a shepherd’s crook shape.

    Fire blight spends the winter in cankers or wounds on the plant and resumes bacterial growth in the spring. There may be oozing from the canker. It is spread by insects, rain, or pruning. Infection can extend into limbs, trunks, or the root system and can kill the tree. Complete removal of any diseased tissue is critical. Dip clippers into a 1 part bleach, 9 parts water solution between each cut to prevent reinfection. The final cut should be 8-12 inches below the diseased area. The UC Pest Note on Fire Blight contains photos and more information.

    - April, May, June
  • Gophers -

    Our local gophers are also called pocket gophers. They make their presence known with crescent shaped mounds of dirt in the garden. Snacking on plant and tree roots as they tunnel through the soil, they are active year round and can have up to three litters each season in well-watered areas. Gophers also gnaw on irrigation lines and divert water into their tunnels, making it difficult to properly water plants. Adults live about three years. Homeowners can use several methods to control them. Locating the main tunnel is the first step. Placing Macabee or Gophinator or box traps or poison baits are explained in detail in the UC Pest Note on Gophers. Another method involves excluding them with wire fencing. Ultrasonic devices and chewing gum have been tested and are not considered to be effective.

    - May, June, July
  • Integrated Pest Management and Beneficial Insects -

    UC IPM LogoOur gardens contain far more beneficial insects than pests. Any time pesticides are used, both good and bad insects die. This upsets garden ecosystems. Use of pesticides can also pollute waterways and may put our children and pets at risk, along with other environmental consequences. We can dramatically reduce pest problems by practicing  Integrated Pest Management, which includes planting native species, following good cultural practices, and encouraging beneficial insects, such as lady beetles, lacewings and soldier beetles

    - March, April, May, June, July, August, September, October
  • Mosquitoes May Be Breeding In Your Yard -

    According to Santa Clara County Vector Control, many people are unaware they may be raising mosquitoes in their backyard, they offer tips on identifying possible Mosquito Breeding Grounds. UC has created a video titled Don't Let Mosquitoes Breed in Your Yard.

    - May, June, July, August, September, October
  • Powdery Mildew -

    Powdery mildew on squash leaves

    Powdery mildew fungus is a common disease on many plants and produces a white powdery appearance on leaves and sometimes other green parts. It can be found on roses, dahlias, chrysanthemums, peas and squash. Some rose varieties are so susceptible that you would be better off removing the plant.

    Powdery mildew likes warm days and cool nights. General tips: maintain good air circulation, remove summer veggies if heavily infected and clean up well, and plant resistant varieties next year.

    Powdery mildew is difficult to treat—the best method of control is prevention by planting resistant varieties—treatments are discussed in the UC Pest Note on Powdery Mildew and the UC Pest Note for Powdery Mildew on Fruits and Berries.

    - May, June, September, October
  • Rose Care -

    A chemical-free way to keep roses healthy and minimize disease associated with foggy summer mornings is to prune to improve air circulation. Think of your rose bushes as large vases, with open centers. Good air circulation allows the morning dew to dry, and helps prevent rust and powdery mildew. The UC Pest Note on Roses has useful information about rose cultivation, pests, and pruning.

    - May, June
  • Spotted Wing Drosophila -

    Unfortunately, the Spotted Wing Drosophila is infesting local cherry, berry, and some other fruits. Look for holes in the fruit. Once the eggs hatch, maggots develop and feed inside the fruit, causing the flesh of the fruit to turn brown and soft. Dispose of infested fruit. Information on identification and control can be found in the UC Pest Note on Spotted Wing Drosophila.

    - May, June
  • Verticillium Wilt -

    Verticillium wilt is a soil-borne fungal disease that damages plant veins. The damage is characterized by affecting one side of the plant. The leaves may wilt and turn brown, dying upward from the base of the branch to the tip. Dead leaves often fall, but may not. Mildly affected plants may survive if fertilized and encouraged into vigorous growth. The fungus can live for years in the soil.

    Planting tomatoes, peppers, eggplants, and potatoes (all members of the Solanaceae or nightshade family) in the same place no more than once every three years helps reduce the fungal population to non-harmful levels. Soil solarization may eliminate Verticillium wilt from infected soils. Crop rotation with cereals or broccolis can reduce the pathogen. Avoid high nitrogen fertilizers. Plant Verticillium wilt-resistant varieties of tomatoes, potatoes or strawberries. Refer to the UC Pest Note information on Tomato, Potato, and Strawberry for species-specific suggestions.

    - May, June, July, August
  • Weed Management -

    Whichever variation of “One year’s seeds makes seven years’ weeds” you prefer, the truth remains: a key part of weed control is not letting them go to seed. For best results, work on removing weeds before they go to seed, and when the ground is moist. Hand pulling and hoeing are effective methods for killing many common weeds. Knowing what kind of weeds you have can be helpful in choosing the best management method - to learn more, see UC's Weed Gallery for help identifying weeds and the UC Pest Note on Weed Management in Landscapes for information about control.

    - February, March, April, May, June, July

Top of page

Webmaster Email: webmaster-mgsantaclara@ucanr.edu