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

September 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. Also, refer to our list of tips useful for any month.

All data grouped by category by Months applicable : September

1. To-do

  • 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.

    - 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, Any month
  • Winter Squash Harvesting -

    Winter squash is ready to pick when the stem begins to shrivel. Press the rind with your fingernail, it should resist denting. Pick before the first hard frost and cure by letting it lie in the sun for at least 3 days, turning it each day. Store in a cool, dry place. It will keep for up to 5 months.

    - September
  • Yellowing Leaves on Gardenias -

    Chlorosis is usually caused by a lack of iron in the soil. With a mild case, the veins remain green and as it becomes more severe will turn completely yellow. Treat the soil with iron chelate according the package directions.

    - September
  • Grass Cycling -

    Leave the clippings on the lawn when mowing. This provides nitrogen for the lawn.  Mow frequently so that no more than 1/3 of the length of the grass blade is cut in any one mowing. Grass decomposes rapidly and very little thatch is formed. Small amounts of thatch can actually be beneficial to a lawn, serving as a mulch. Many parks and golf courses have been doing this for years. Other uses for grass clippings include mulching for weed control and as a great addition to your compost pile. There are some cities that no longer will allow grass clippings in their dumps.

    - June, July, August, September
  • Deep Watering Trees -

    Even if a tree gets watered every time the lawn does, it needs deep watering twice during the summer. Use a soaker or drip hose around the tree at the drip line and let it slowly drip for 2 to 3 hours. A mature ornamental tree or street tree may not need any water. Mature fruit trees should watered by filling a watering basin around the tree every three or four weeks. Young fruit trees need watering every two weeks. Don't let lawn sprinklers hit tree trunks as this may cause crown rot and damage the tree.

    - July, August, September
  • Garden Sanitation -

    Remove spent blossoms, fruit, and other plant parts as your plants finish producing. Dead and decaying plant parts can attract pests and give them safe places to breed. If pests are given a nice place to spend the winter, their populations are likely to be much higher next year.

    - July, August, September, Any month
  • Worm Composting -

    Worm compostingWorm composting also called vermiculture or vermicomposting is a convenient way to decompose kitchen waste and provide nutrient-rich soil amendments for your vegetable garden.

    Here is a description for Getting Started.

    The Santa Clara County Home Composting Education Program offers Worm Workshop classes.

    - February, June, 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).

    - April, May, June, July, August, September, Any month
  • How to Tell if Fruits and Vegetables Are Ready to Pick -

    The UC Davis Postharvest Technology website was designed for commercial growers, but the information on how to tell When Fruits and Vegetables are Mature is handy for home gardeners as well. There's also information about how to Store Fruits and Vegetables for Better Taste.

    - July, August, September
  • Preserving Fruits and Vegetables -

    Interested in how to preserve fruits and vegetables? UC Food Safety has lots of information including "Safe Handling of Fruits and Vegetables", "Safe Methods of Canning Vegetables", "Chart on Storing Fresh Fruits and Vegetables", and more. Visit their web page UC Home Preservation and Storage Publications for more details.

    - August, September
  • Fresh Fruits and Vegetables Without a Garden! -

    If you like the freshest possible produce but don't have the space or time to grow your own, find a certified Farmers Market or a farm selling directly to consumers. The County of Santa Clara website has a Farmers Market page with links to certified Farmers Markets and the Country Crossroads map shows where you can buy more than 100 commodities directly the farm source.

    - June, July, August, September
  • Prune Apricot and Cherry Trees -

    Apricot and cherry trees should be pruned at least 6 weeks before the first rain falls. If it rains before the pruning cuts heal, the tree are more susceptible to infection by Eutypa spores that cause dieback. See UC Pest Note on Eutypa Dieback. The UC Home Orchard website has more advice on Pruning Apricots.

    - August, September
  • 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 Landscape Replacement Program!

    - May, June, July, August, September
  • Pinch Tomato Blossoms -

    Tomato blossoms (Photo: Felagund commons.wikimedia.org)In September pinch new blossoms off tomato plants to direct the plant's energy into growing and ripening already formed tomatoes. It takes several weeks to go from blossom to fruit, so the tiny little yellow flowers that are just starting now are unlikely to have time to produce good quality tomatoes.

    - September
  • Free the Trees -

    As your young trees grow bigger and stronger, remove supporting stakes or loosen the straps as early as possible. Some movement of the tree is important to make it healthier in the long run. If the tree is able to stand on its own, it will develop a thicker trunk with a taper at the bottom.

    - September, Any month
  • Keep Watering Until the Cool Weather Arrives -

    September is still a warm month in Santa Clara County. Continue watering established trees and shrubs until temperatures cool down. As a rule of thumb, trees should have a couple of deep waterings during the summer, if you haven't done that, now is a good time. Use a soaker hose or drip hose around the drip line of the tree and slowly water for two to three hours. Mature fruit trees need a bit more, fill the surrounding basin every 3-4 weeks, young fruit trees need water every couple of weeks.

    - September

2. What to plant

  • Cool Season Vegetables -

    cool season vegetablesMany cool season vegetables can be planted in our Bay Area gardens in September. These include beets, radishes, peas, spinach, broccoli, cabbage, and bok choy. During our winters, nature helps with the watering, there are fewer weeds and pests, and harvesting can be done at a relaxed pace to due natural refrigeration. Check out our recommended times to plant vegetables in Santa Clara County and keep an eye out for our Fall Garden Market plant sales.

    - September
  • 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
  • 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. The Honey Bee Haven website has more resources, including a list of plants they grow.

    - March, April, May, June, September, October
  • Tree help -

    The city of San Jose has multiple resources for the home gardener. See their webpage on tree care. Oak trees (valley, live, blue), big leaf maples, and buckeyes are great choices for our region.
    SelecTree: A Tree Selection Guide from CalPoly can help with selecting the right tree for the right place in your landscape.     
    Apply for stewardship of one or more trees for 3-5 years at Our City Forest.

    - September, October, Any month
  • Carrot Culture -

    carrotsIf you have a light fluffy soil, perhaps in a raised bed, you can grow those long beautiful carrots you see in the grocery store. However most of us have a heavy clay soil and it is best to grow the shorter varieties. Adding organic material such as compost rather than manure is good. The seeds are very tiny and mixing sand with them will help you not over-seed. Plant no more than 1/2 inch deep. Carrots are slow to germinate and could take as long as 3 weeks. Keep the soil moist until they're up. Thin to 2 or 3 inches apart. Plant every few weeks for a continuous crop. If you have limited space, try growing in among your ornamentals, their feathery tops can look quite pretty. They can also be grown in a container. Some common problems are twisted roots from planting too close together, forked or deformed roots from clods and rocks in the soil, hairy root from too much nitrogen and splitting from too much water.

    - September

3. Pests and Diseases

  • Eutypa Dieback on Apricot Trees -

    Apricot Trees: The sudden dieback of individual branches during mid to late summer can lead to dry brown leaves that may remain on the branches until the following winter. This is due to a fungal parasite caused by airborne spores that enter fresh pruning wounds. Cankers develop around an infected wound and eventually kill the branch. Death can take months or even years. The danger of spreading is highest in the fall during early rains and again in the spring. Prune apricot trees in July or August before fall rains begin. For further information consult UC Pest Note on Eutypa Dieback and Bot Canker.

    - July, August, September
  • 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

    - April, May, June, July, August, September, October, Any month
  • 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
  • Mosaic Virus -

    Mosaic virus on squash and cucumber plants is a disease spread by aphids and cucumber beetles. The leaves become rough and mottled, the plant becomes stunted and the fruit can be whitish. Pull the plant and put it in the trash. Do not compost. For more information see UC Pest Note on Squash Mosaic Virus.

    - September
  • Neem Oil -

    Neem oil is an approved pesticide in California for use on ornamental and food plants. It is derived from the neem tree. Aphids, caterpillars, loopers, mealy bugs, thrips, whiteflies, and diseases like mildew and rust are effectively controlled. It is most effective when alternated with insecticidal soap or pyrethrum, killing problem insects in different stages of development. Follow label instructions. Spray 2 or 3 times from 7 to 10 days apart. As with all horticultural oils, do not spray if daytime temperatures will exceed 90°F.

    - September
  • Rats -

    Have you found snail empty shells stashed in out of the way places, hollowed out Navel oranges, Meyer lemons with no skins, tomatoes with bite marks, fruit with holes gnawed in them or grape skins or cherry tomato skins scattered around? This could indicate the presence of rats. The UC IPM Pest Note on Rats provides a wealth of scientific information.

    Rats show up when your citrus, tomato or fruit first start to ripen. Rats are agile climbers and usually live and nest in shrubs, trees, and dense ground cover like ivy. Good sanitation is required. Garbage and garden debris should be eliminated. Use tight fitting lids on garbage cans. Thin out dense vegetation to make the habitat less desirable. Mow ivy once a year to the ground. Climbing ivies on fences or buildings should be removed.

    Trapping is the safest and easiest method for controlling rats. The simple snap trap is effective. The most important thing about trapping rats is to have lots of patience and keep trying. Wet some oatmeal enough for it to hold together, add dog or cat kibble or bits of lightly cooked bacon mixed in. Tie a walnut to the trigger and add a dab of peanut butter.

    Other baits to try are peanut butter and fresh fruit, but try to have something tied to the trigger. Set traps where rats are likely to travel or where you see droppings along fence lines or buildings. Bait the trap but do not set it for several days. Try different baits in multiple traps until you find one the rats like. Put two traps facing each other. After the rats are accustomed to being fed, then set the traps. If the rat springs the trap but doesn't get caught, move the traps to a different place and change to different baits. Rats prefer secluded spots and will be less wary there. Be sure to secure the trap with a wire or nails. Above all be patient and use multiple traps.

    - March, April, July, August, September, Any month
  • Leafcutter Bees - a Beneficial Insect -

    leaf damaged by leafcutter beeDo your rose bush leaves have smooth round holes in them? The likely culprit is the female leafcutter bee. The bee cuts smooth round or oval leaf fragments and uses them to line each underground brood cell that she fills with nectar and pollen. When the cell is ready, a single egg is sealed inside. The larva pupates (matures) in the chamber and emerges in the spring.

    Rose leaves seem to be their favorite. The hole in the leaf is much larger than an ordinary caterpillar would make and is very smooth as if a miniature cookie cutter was used. The bee can chew off a leaf fragment in less then a minute with its sharp jaws.

    Like all bees, leafcutter bees are important pollinators and should not be killed.

    - September
  • Spider Mites -

    Spider mites are closely related to spiders and are about the size of the period on this sentence. They feed on many kinds of plants. They suck out plant juices from leaves, flowers and the blossom end of fruit. Plant leaves may become stippled with yellow and webs may be visible. Hotter temperatures and dusty conditions encourage them. Conserving natural enemies by not using pesticides, providing sufficient irrigation and reducing dust may all help control mites. Periodic washing of leaves with water can be very effective in reducing their numbers. If treatment is necessary, spider mites can be controlled with insecticidal soap, horticultural oil or neem oil. Releases of predatory mites have been used in some situations. More information is available in the UC Pest Note on Spider Mites.

    - July, September
  • 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.

    - May, June, July, August, September
  • Birds -

    Birds can cause extensive damage to tree fruit crops. Unlike squirrels, birds are more likely to peck at one piece of fruit until it’s gone. If they are doing too much damage, netting over a tree can keep them away from the fruit. If you use visual repellents (such as Mylar streamers or noisemakers) to frighten them, be sure to vary the method so that the birds don’t become immune to the effects. Read the UC Pest Note on Birds on Tree Fruits and Vines for more information.

    - July, August, September
  • 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 mosquito tips including identifying possible breeding grounds. UC has created a Youtube video titled Don't Let Mosquitoes Breed in Your Yard.

    - May, June, July, August, September, October
  • Tomato blossom end rot -

    Tomato blossom end rotA brown depression on the bottom of tomatoes is usually blossom end rot. This disorder is related to a calcium deficiency aggravated by irregular watering. Since most soils have adequate calcium, watering is usually the problem. Without regular watering, the calcium in the soil cannot reach the plant. Mulching can help. Water tomatoes regularly. Avoid flooding them so the roots sit in water.

    - July, August, September
  • Sooty Mold -

    Aphids, scale, mealybug and whitefly all excrete sticky honeydew that is colonized by sooty mold fungi. By itself, the fungi cannot kill the plant but it can coat the leaves to the extent that sunlight is prevented from reaching the leaf surface. A strong stream of water will wash the mold off leaves. The mold can be washed off fruit with mild soap and water. See UC Pest Note on Sooty Mold for more information.

    Ants protect the sucking insects from their predators in order to eat the honeydew. Keep ants out of trees and away from honeydew-producing insects by applying a sticky compound such as Tanglefoot on a tape wrapped around the trunk.

    Trim tree limbs touching buildings, fences or other access points as well. Baits such as ant stakes placed under trees and shrubs may help reduce ant foraging in some cases.

    For ant information, see the UC IPM Pest Note on Ants.

    - August, September, October, November
  • Brown Marmorated Stink Bug -

    Native to Eastern Asia, this pest was introduced to the United States in the 1990's and has been found in Santa Clara County. Described as “one of the worst invasive pests we’ve ever had in California” by UC Cooperative Extension advisor Chuck Ingels, this insect affects many different crops and is a serious residential problem. There's more information in the UC Pest Note on Brown Marmorated Stink Bug. View a map showing the distribution of the BMSB in California.

    Adult (top) and mature nymph of the brown marmorated sting bug
    Adult (top) and mature nymph of the brown marmorated sting bug

    - August, September
  • Bitter Pit (Brown Spots) on Apples -

    Bitter pit is a physiological disorder that affects many varieties of apples. The condition develops after fruit has been picked. It is caused by low levels of calcium in fruit tissues which leads to small brown, sunken lesions that become dark and corky. Highly susceptible cultivars include Red Delicious, Granny Smith, Golden Delicious, Jonathan and Gravenstein. The UC Bitter Pit Pest Note recommends cultural practices for control.

    For even more information, the UC Postharvest Technology Center website has grower information, including using calcium sprays starting in June.

    - August, September
  • Whiteflies -

    Whiteflies are tiny, sap-sucking insects that may become abundant in vegetable and ornamental plantings, especially during warm weather. They excrete sticky honeydew and cause yellowing or death of leaves. Outbreaks often occur when the natural biological control is disrupted. Management is difficult once populations are high.

    Whiteflies use their piercing, needlelike mouthparts to suck sap from phloem, the food-conducting tissues in plant stems and leaves. Large populations can cause leaves to turn yellow, appear dry, or fall off plants. Like aphids, whiteflies excrete a sugary liquid called honeydew, so leaves may be sticky or covered with black sooty mold that grows on honeydew (See UC Pest Note on Sooty Mold). The honeydew attracts ants, which interfere with the activities of natural enemies that may control whiteflies and other pests.

    Management of heavy whitefly infestations is difficult. The best strategy is to prevent problems from developing in your garden or landscape. In many situations, natural enemies will provide adequate control of whiteflies; outbreaks often occur when natural enemies are disrupted by insecticide applications, dusty conditions, or interference by ants. Avoid or remove plants that repeatedly host high populations of whiteflies.

    In gardens, whitefly populations in the early stages of population development can be held down by a vigilant program of removing infested leaves or hosing down with water sprays. Reflective mulches can repel whiteflies from vegetable gardens, and yellow sticky traps can be used to monitor or, at high levels, reduce whitefly numbers. If you choose to use insecticides, insecticidal soaps or oils such as neem oil may reduce but not eliminate populations. Systemic insecticides may be more effective but can have negative impacts on beneficial insects and pollinators.

    For more information see UC Pest Note on Whiteflies.

    - June, July, August, September

Webmaster Email: webmaster-mgsantaclara@ucanr.edu