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The amount of water a tree needs during the summer months depends in large part on the age of the tree. Photo courtesy Getty Images.

Do you have a gardening question? The UC Master Gardeners of Santa Clara County can help. Our volunteers are part of the University of California’s Cooperative Extension program, and we are trained to use research-based information to educate residents on sustainable gardening and landscaping practices specifically for our area.

Our monthly “Ask a Master Gardener” column will answer your questions and offer tips. Have a question? Email lifestyle@embarcaderopublishing.com..

How do I know how much water my trees need during the hot summer months?

The amount of water trees need in the summer depends in large part on the age of the tree. Newly planted trees with shallow roots may need weekly water. Trees that are a few years old and fairly well established may need monthly watering. Mature trees with extensive root systems may not need any supplemental water. 

These are just very general guidelines. 

It is essential to know the water requirements of the plants. You can determine these by researching the cultural needs (factors that impact a plant’s growth and longevity)  or knowing their native habitats, the soil type and how well it retains water, and the micro-climate (shaded, windy, dry etc.) in which the tree is located . The UC WUCOLS database has information on the water needs of over 3,500 plants used in California landscapes. 

Always water slowly and deeply to penetrate down to the roots.  Use a soaker or drip hose around the tree at the drip line and let it slowly drip for 2 to 3 hours. Don’t let lawn sprinklers hit tree trunks as this may cause crown rot and damage the tree.

UC Master Gardeners looking for volunteers

If you love gardening, have an interest in science-based horticulture and would enjoy volunteering to share your knowledge with the public, becoming a UC Master Gardener volunteer may be for you! University of California Master Gardeners volunteers are trained to give talks and classes, staff the help desk, work in demonstration gardens, answer questions at events and much more.

Santa Clara County has begun to recruit for its 2025 Master Gardener Training Course. It starts by attending a mandatory information session in late August, then going through an application and interview process. Those who are selected will start an intensive training course starting in January and continuing through May. In this course, you will be steeped in fascinating horticulture topics taught by UC faculty and participate in hands-on workshops. Upon graduation, you will be joining a group of like-minded gardeners ready to share your knowledge
with the public. Here’s how to apply, and we hope you will!

Tomato plants are shown here growing in cages. Photo courtesy Getty Images.

July gardening tips

Check your plants for aphids

Almost every plant has an aphid species that feeds on it. Aphids reproduce quickly — some adults produce 80 offspring a week! Check plants twice a week during rapid growth. 

Knock off aphids with a strong water spray or prune affected leaves. If necessary, use insecticidal soaps and oils like neem or canola oil, being careful not to spray natural enemies like lady beetles.

Use row covers on new plants and avoid overfertilizing with nitrogen.  Ants protect aphids so here are ways to control them. Mature plants tolerate moderate aphid populations, and biological controls often resolve the problem.

Keep suckers on tomatoes grown in cages

Pinching out suckers (shoots) is recommended for areas with a short growing season (for faster production) or humid summers (to improve air circulation) or to make it easier to tie plants to stakes. With our dry climate and long growing season, there’s no need to remove them if you’re growing tomatoes in cages. Letting suckers grow provides foliage cover to shield the fruit from direct sun, gives additional photosynthesis and will produce more fruit. Feel free to remove interior leaves that are shaded out or turning yellow, or clip foliage as needed to make the tomatoes easier to find and harvest. Here’s more information on growing tomatoes. 

Give extra care to melons

By this time of the year, melon vines have probably spread out  – and with a lot of flowers. Now would be a good time to apply a foliar spray of a water-soluble fertilizer to give them a nice boost. Keep the water flowing as they are one of the thirstiest plants you can grow. You can set young melons on the top of inverted cans (coffee cans, tuna cans, etc.) to warm them faster and more evenly. Punch a hole in the bottom of the can so water won’t puddle and rot the melon. Melons will begin ripening in August. 

How will you know when it’s ripe? The background color behind the netting will turn from green to tan. The stem will slip right off with just a light touch. Last but not least, let your nose tell you if it’s ripe. Smell the stem end; it should have a wonderful melon aroma. The color and smell test also works well in the grocery store.

Weed out bindweed

Have you seen a pretty, morning glory-like flower on a vine that winds through any plant within reach? Field bindweed is one of the most challenging weeds to control because its roots can reach depths of 20 feet or more, and it readily regrows from root fragments as short as 2 inches. The only chance of controlling this invasive weed is to stay right on top of it and remove it as soon as you see any of it peeking up out of the ground. Every time it starts growing above ground and photosynthesizing, it is storing energy in the roots. This allows it to put out new shoots. It produces many seeds which remain viable for years. Making things even worse, it’s drought tolerant. Controlling it isn’t easy, but this UC pest note discusses options. Chemicals aren’t needed if you’re persistent in removing new growth to prevent seed production and limit the plant’s ability to store new energy in the roots.

Consider planting chrysanthemums now

This is a less common but good time to plant chrysanthemums. They will have plenty of time to develop a good root system before the cold winter and are more likely to bloom perennially in your garden than if they are started in the fall. You also can start chrysanthemums from cuttings. Plant them in amended, well-drained soil, or grow them in a large container. Keep them moist but not wet. They do well in full sunshine, yet a little afternoon shade is fine in hot areas. If you pinch the growing tips as they grow, they will branch and be bushier. Otherwise, be prepared to provide support if they grow tall. Also, pinching off some of the buds will result in fewer yet much larger blooms. There is a Bay Area Chrysanthemum Society for local information and sharing.  

July gardening events

Ask questions or listen in at our monthly Zoom Plant Clinic, which is held the second Tuesday of the month from 7:00 – 8:30 p.m.  Dates for 2024 are July 9, Aug. 13, Sept. 10 and Oct. 8.

You can also subscribe to our monthly Tips and Events newsletter and to our seasonal Thyme to Garden blog.  San Mateo residents can also find gardening advice on the UC Master Gardeners of San Mateo and San Francisco website.

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