April Tips & Events for Santa Clara County
“Gardening requires lots of water—most of it in the form of perspiration.”
~Lou Erickson
Monthly Tips
Quiz: How Can You Prevent the Spread of the Oriental Fruit Fly?
A large part of Santa Clara County is in a quarantine zone to prevent the spread of the invasive oriental fruit fly. These pests damage fruit and vegetables by laying eggs under the skin which hatch into maggots that tunnel into the fruits. They “hitchhike” on infected fruits and vegetables that are transported to other areas, often through shared homegrown produce. An infestation is a huge threat to California’s fruit industry. Scroll to the bottom to learn how to help prevent the spread of this invasive fruit fly.
Photo: Adult female oriental fruit fly, Bactrocera dorsalis (Hendel), laying eggs by inserting her ovipositor in a papaya, Scott Bauer, USDA
Oriental fruit fly
Two happy customers holding boxes with their new plants at a previous spring garden fair
Photo credit: Barbara Krause
April 27 Spring Garden Fair Features Gardening Help and Plant Sales
You won’t want to miss this one! The annual Santa Clara County Master Gardeners Spring Garden Fair is a much-anticipated educational event and plant sale that kicks off the summer gardening season for thousands of local home gardeners. You can buy tomato, pepper, herb, ornamental, succulent, and native plant seedlings, all grown at Martial Cottle Park and chosen specifically for our local climate and conditions. It’s a learning opportunity too, with a variety of expert gardening talks, information tables, and Q&As with Master Gardeners—plus fun kids activities. Join us!

  • Master Gardeners Spring Garden Fair
  • Saturday, April 27, 9:00 am–2:00 pm
  • Martial Cottle Park, 5283 Snell Avenue, San Jose
  • Directions
  • Free admission
Join Our Public Tomato Trial
Want to be a citizen scientist? Join our public tomato trial! Here’s how it will work:
  • Sign up to participate.
  • Buy the three chosen trial tomatoes at our Spring Garden Fair.
  • Report on your results over the growing season.

By having lots of people growing these varieties in home gardens all over the county, we will learn how they perform under a wide range of conditions. Then we can decide whether to add them to our tomato offerings in the future. We look forward to working with our fellow tomato enthusiasts!
Photo: Bronze Torch grape tomato, Renee’s Garden
Tomato Bronze Torch courtesy Renees Garden
Photo: Culex mosquito biting through human skin, by J.K. Clark
Did you know that there are more than 50 species of mosquitoes found in California? Several of these species bite people and some can spread diseases such as West Nile virus or encephalitis. Mosquitoes lay eggs directly on or near water, in as little as a bottle cap. Some eggs can survive dry conditions for months. Once there is enough water to flood the eggs, they will hatch and develop to adulthood in less than a week in ideal conditions.

You can help to keep mosquito populations low. Start by draining any standing water or treating it with a control agent such as Mosquito Dunks. In isolated ponds, incorporate mosquito-eating fish. Sign up for this webinar to learn more about mosquitoes (& ticks!) and how to protect yourself.
Check Soil Temperature before Planting
Picture of a soil thermometer probe showing a 50 degree Fahrenheit temperature
The days are getting longer, so it must be time to plant summer vegetables, right? Well, maybe not yet. Even a warm April day doesn’t mean your soil has given up its winter chill. Planting in cold soil results in slow germination, increased risk for rot from damping off, and even stressing plants for the rest of the season.

You can use a soil thermometer to check soil temperature directly (see the link below for instructions). UC lists soil temperature conditions for vegetable seed germination or use our vegetable planting chart to look up the months best suited for planting.

Photo credit: Allen Buchinski
Use Floating Row Cover to Protect Seedlings
Floating row cover
Floating row cover is a lightweight material that you can use to protect seedlings in a variety of ways:

  • Suspend it over newly planted seedlings to shade them from the hot sun.
  • Tightly enclose plants to exclude insect pests such as leaf miners or flea beetles.
  • Lay over newly planted seeds or seedlings to keep birds from eating the tender sprouts.
  • Isolate plants to prevent undesired cross-pollination if needed when saving seeds.

The material is light enough for plants to lift it up as they grow, as long as you leave enough slack. Row cover is available from nurseries or online.

Photo: A bed of plants protected with row cover, Susan Mahr, University of Wisconsin Master Gardener
Quiz Answer: Stop the Spread of the Oriental Fruit Fly
Am I in the quarantine area?
Look up your address or check this map. If you’re in the quarantine area, don’t move any homegrown fruits or vegetables from your property.

What fruits and vegetables are susceptible?
All stone fruits, all citrus, avocados, vegetables like tomatoes and peppers, and many other fruits. See the USDA oriental fruits fly FAQ under What’s at Risk. 

Can I give away homegrown fruits and vegetables?
Only if you process them first. Cook, juice, or dehydrate them before sharing.

How should I dispose of the fruit?
Double-bag fruit — including all dropped fruit — in plastic bags and throw them in the garbage bin. Don’t add them to your compost pile.
Figs - cherries - apricots and oranges are some of the fruits that can host the oriental fruit fly
Photo: Figs, cherries, apricots, and oranges are some of the fruits that can host the oriental fruit fly. Photo credit: Orange slices: Unsplash, All others: Pixabay
Upcoming Events
Our monthly Plant Clinic Online is an opportunity to chat with a Master Gardener via Zoom to diagnose a plant problem. You can also listen and learn while other people ask questions. It takes place on the second Tuesday of the month (April 9), from 7pm - 8:30 pm. Priority will be given to questions that are emailed in advance; instructions are in the Zoom registration confirmation. Registration required.

Composting Workshop at the SoFA Pocket Park, Friday, April 5, 5:30–6:30 pm, SoFA Pocket Park, 540 S. 1st Street in San Jose, San Jose

GRP Citrus Planting and Care, Saturday, April 6, 9–11:30 am, Guadalupe River Park Historic Orchard, 425 Seymour Street, San Jose

SCTDG Planning Your Summer Vegetable Garden, Saturday, April 6, 10 am–noon, South County Teaching and Demonstration Garden, 80 Highland Avenue (Corner of Monterey Road & Highland Avenue), San Martin

PADG Plan for Your Summer Vegetable Garden, Saturday, April 6, 10–11 am, Palo Alto Demonstration Garden, 851 Center Drive, Palo Alto

How to Attract Bees, Butterflies, and other Pollinators to Your Garden, Saturday, April 6, 10:30–11:45 am, Willow Glen Public Library, 1157 Minnesota Avenue, San Jose

Growing Tomatoes: The Basics Still Count, Saturday, April 6, 1–3 pm, Sunnyvale Teaching and Demonstration Garden, Charles Street Gardens, 433 Charles Street, Sunnyvale

The Joy of Summer Vegetables, Tuesday, April 9, 6:30–7:30 pm, Online

Growing Culinary Herbs in Your Garden, Tuesday, April 9, 6:30–7:30 pm, Morgan Hill Public Library, 660 W. Main Avenue, Morgan Hill

Plant Clinic Online, Tuesday, April 9, 7–8:30 pm, Online

Growing Great Tomatoes, Tuesday, April 9, 7–8:30 pm, Saratoga Library, 13650 Saratoga Avenue, Saratoga

Learn to Successfully Grow Tomatoes: Garden Talk and Tour, Saturday, April 13, 10 am–noon, McClellan Ranch Demo Garden, 22221 McClellan Road, Cupertino

Enhancing Pollinator Gardens, Saturday, April 13, 11 am–12:30 pm, Milpitas Library Auditorium, 160 North Main Street, Milpitas

Growing Summer Vegetables, Saturday, April 13, 11 am–12:30 pm, Berryessa Public Library, 3355 Noble Avenue, San Jose

MCP Guided Tours of the Master Gardeners Native Entrance Gardens, Sunday, April 14, 10 am–4 pm, Martial Cottle Park, 5283 Snell Avenue, San Jose

Growing Warm Season Vegetables, Tuesday, April 16, 7–8 pm, Orchard City Banquet Hall - Campbell Community Center, 1 W. Campbell Avenue, Campbell

Now Is the Time for Homegrown Tomatoes, Wednesday, April 17, 7–8:30 pm, Los Altos Library, 13 S. San Antonio Road, Los Altos

Mosquitoes & Ticks of Public Health Concern, Thursday, April 18, noon–1 pm, Online

Garden Workshop: Spring Garden Demonstration, Saturday, April 20, 9 am–noon, Everett, 2380 Monroe Street, Santa Clara

Container Gardening for All Seasons, Tuesday, April 23, 6:30–8:30 pm, Fremont Unified High School Adult Education, 589 W. Fremont Avenue, Sunnyvale

Spring Garden Fair - Martial Cottle Park, Saturday, April 27, 9 am–2 pm, Martial Cottle Park, 5283 Snell Avenue, San Jose
Check our calendar for the latest schedule of events. Videos of many past presentations are also available.
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University of California Master Gardener volunteers promote sustainable gardening practices and provide research-based horticultural information to home gardeners. Visit our website for more information including:

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