July 2025: Vole Invasion

Protecting the growing plants from hungry critters is an ongoing challenge in the Edible Demo Garden. Wire mesh is used extensively under planting beds and around the straw bales to discourage gophers. Yards of protective netting keep the birds and rabbits from eating young seedlings and ripening fruit. Through vigilance and determination, EDG volunteers have usually managed to reduce damage to crops from the vertebrate garden dwellers. However, this spring volunteers noticed that something was eating the summer squash plants in the straw bales in the area known as the “back 40”. Whatever it was had to be small enough to slip around and under the gopher-repelling wire mesh. Some little holes in the bales and on the ground nearby pointed to voles as the most likely culprits.

What are Voles?

Voles are small, chunky, ground dwelling rodents with short tails. They are also called meadow mice, but they are not mice or rats. They belong to a separate genus and are more closely related to lemmings. The most common of the five species of voles in California is the California vole, Microtus californicus. It is four to six inches long with grayish brown fur, a blunt nose, and small eyes and ears. Voles are herbivores. Although their favorite foods are grasses and herbaceous plants, they can cause extensive damage to edible crops. 

How do you know if voles are in your garden?

Voles are active both day and night, but primarily around dawn and dusk. They hide in dense underbrush and in their shallow burrows, so they are not easy to spot. Voles are extremely prolific and mature rapidly with females bearing multiple litters per year.

Once you notice plant damage and suspect voles, look for burrows with numerous openings, about one to two inches in diameter, connected by narrow pathways. The pathways may be littered with droppings and plant fragments. Unlike gophers and moles, voles do not pile up soil around their burrows. 

What can you do to control voles?

The first step to controlling voles is to make your garden less welcoming. Because they only like to travel a short distance to a food source, removing the vegetation they depend on for cover will discourage voles and prompt them to go elsewhere. Weeds and grasses provide hiding spaces, so creating a vegetation-free zone around a garden area will deter them. Unfortunately, they found both the food and cover they needed in the straw bales in the EDG garden.

In ideal circumstances, vole populations stay in balance, providing food for predators. Their lives are short, most living less than a year. They are snacks for owls, hawks, coyotes, foxes, and snakes. Populations also fluctuate with peaks every two to five years. 

When vole populations are high and removal of vegetative cover and physical barriers are not sufficient to control them, snap-type mouse traps can be used with varying success. Traps should be placed at right angles to burrow pathways with the trigger end in the pathway so that voles will trip it as they pass over. Flooding or fumigating burrows does not usually work because of the shallow and open structure of the burrows. Poison bait, while effective, increases risk to pets, wildlife and humans and should never be used in edible gardens during the growing season. 

What are the options for an organic edible garden?

While numerous home remedies and repellents have been suggested, none have been shown to be reliably effective against voles. Possible repellents include coffee grounds, cayenne pepper, castor oil, and garlic. Voles don’t like plants with strong odors and unpleasant tastes. They avoid plants in the allium family like onions and garlic and find daffodils, marigolds and castor beans distasteful. Several of these options were considered for the Edible Demo Garden. Coffee grounds were ruled out as not certifiably organic. Claims that sprinkling cayenne pepper around garden plants discourages voles prompted the EDG volunteers to plant hot peppers among the squash vines. Subsequently, damage to the plants appeared to decrease so maybe it worked, or possibly one of the snakes recently spotted in the garden is reducing the vole population.

Click here to learn more about voles.

Natives are welcome in the Edible Demo Garden. As a joint project with the Native Plant Guild in October 2021, garden volunteers planted a variety of sun-loving, drought tolerant California natives in a corner of the garden area. Some have flourished and some have not, but that’s what happens in a demonstration garden. It’s all about learning what plants need and the conditions that suit them best. The primary goals of the project were to provide year-round beauty and attract pollinators. It turns out that there are even more reasons why native plants benefit an edible garden.

Native Plants Attract Pollinators and Invite Beneficial Insects

The blooming periods of native plants coincide with the times when pollinators are most active, and these can overlap with the flowering times of vegetable plants. Native plants that flower in early spring can bring in pollinators before vegetable blossoms emerge. This is particularly important for native bees who are even more efficient pollinators than honeybees. Fall blooming native plants help to create a steady supply of food and resources to keep the pollinators around and encourage them to overwinter in the garden.

Native plants also invite beneficial insects that are natural enemies of vegetable garden pests. Beneficials such as hoverflies, lady beetles, and lacewings go where they find the herbivorous insects they like to eat. It doesn’t matter to them whether their prey is on an edible plant or a native. The natives keep the beneficial insects nearby, so they are there to control pests when the vegetable crops are planted.

Native Plants Improve Soil Health

Native plants support soil biodiversity by providing habitat for beneficial microorganisms like fungi and bacteria. Some can act as nitrogen-fixers to improve soil fertility. Natives with deep root systems can improve soil structure by creating channels through which water and nutrients can penetrate. When the roots and leaves of the native plants die back, they add organic matter to the soil reducing the need for soil amendments.

Native Plants are Low Maintenance

Natives don’t need fertilizing and require little watering once they are established. While some need deadheading and cutting back, it’s best to minimize the kind of tidying up that’s done in the edible garden. The native plants can offer a refuge for beneficial populations, providing them with undisturbed nesting and overwintering sites. Ideally the native plants attract enough beneficial insects and other natural enemies to maintain a healthy balance so that pests are kept in check.

Occasionally a native plant can require more severe pruning. Recently a Coyote Brush, Baccharis pilularis, adjacent to the Edible Demo Garden, grew too large and began to produce an abundance of the fluffy white seeds typical of the female flowering plant. Although some classify Coyote Brush as a weed, it is a keystone plant which has significant value in a habitat garden. Armed with saws and pruning tools, the volunteers cut the overly ambitious native down to a manageable size.

Native Plants Add Beauty and Interest

Native plants bring unique beauty to the garden. The natives planted in the Edible Demo Garden were initially chosen to provide blooms throughout the year. Some flower early and bring color into the winter garden and others extend their blooming period into late fall. They add contrast to the flowering of the vegetables and fruit trees. Ceanothus ‘Concha’ now masks the compost bins with its copious cobalt blue flowers in early spring.  Coast Aster, Aster chilensis, provides bright, daisy-like blossoms throughout summer and fall. Bees and hummingbirds enjoy the showy red tubular blooms of California fuchsia, Epilobium, into late fall. The goal to bring native plants into the Edible Demo Garden to provide year-round beauty has been achieved.

For more information on growing native plants, click here.

Tomatoes are among the top summer crops in the Edible Demo Garden and each year there are decisions to be made about which varieties to grow. Since there are reported to be over 10,000 varieties of tomatoes, it’s important to narrow down the selection considerably and plant only those varieties that grow well in Marin and are appealing to consumers. However, even within those broad parameters, many choices can be made. The Marin Master Gardeners typically offer sixteen varieties in their annual tomato plant sales. These are the varieties that have proven over the years to be the most popular with customers. Each year one or two new varieties may be offered to replace some that have not fared so well in terms of sales or customer reviews. Choices about new varieties are usually based on members’ recommendations.

The Tomato Experiment

This spring the Edible Demo Garden and the Edibles Guild launched a collaborative experiment to determine which of seven tomato varieties not previously sold in the tomato market, would be most successful in Marin’s different growing conditions. The experiment involved adopting out 132 plants grown in the Indian Valley Organic Farm & Garden greenhouse to 37 Marin Master Gardeners willing to try growing them in their own gardens. The seven varieties were:

• Costoluto Genovese – a classic red Italian heirloom
• Bicolor Marvel Stripe – a marbled red and gold heirloom
• Moonglow – a bright orange heirloom
• Mortgage Lifter – a large meaty red heirloom
• Magic Bullet – an elongated cherry-sized open pollinated variety
• Pink Berkeley Tie Dye – a wine-colored open pollinated variety with green stripes and pink flesh
• Amish paste – a small bright red heirloom best used for sauces

The tomato adopters agreed to submit data describing their experiences growing the trial tomatoes. They recorded the garden type, location, and microclimate, when the tomatoes were planted, how they were cared for, and when the first tomato was harvested. Then they subjectively rated the tomatoes on yield and taste. Finally, and most importantly, they answered the question – “would you grow this variety again?”.

Which varieties had the best results?

Tomato season isn’t completely over in some areas of Marin and the data are still being collected. However, there are some interesting early results. Magic Bullet, the most unique variety in terms of the appearance of the fruit, had high ratings for yield and taste. It was a big producer in the Edible Demo Garden and sold out quickly at the IVC Farm Stand. Mortgage Lifter also stood out due to the beauty and size of the fruit, one tomato weighing over 1.5 pounds. That variety reportedly earned its name after it was so successful that the original developer was able to pay off his mortgage in six years (that was back in the 1930s). Amish Paste, was a disappointment, ending up at the bottom of the list for yield and taste. The other varieties were rated somewhere in the middle. So far, the majority of the Master Gardeners who grew Bicolor Marvel Stripe, Mortgage Lifter, Magic Bullet, or Pink Berkeley Tie Dye, responded either “yes” or “maybe” to the question about whether they would grow that variety again.

What matters most when choosing tomatoes to plant

One of the most important factors to consider when choosing a tomato variety is the microclimate in the growing location. Tomatoes need sunshine and warm soil. All the experimental tomatoes required temperatures above 65 degrees and some preferred 75 degrees. During a typical spring, in most areas of Marin, around May 1^st is when the temperatures are best for planting tomatoes. Tomatoes planted before the air and soil are sufficiently warmed, will sit idly by until the conditions are right. Conversely, tomatoes don’t like extreme heat and will stop production during heat waves like those experienced in parts of Marin this summer.

Linked to microclimate are days to maturity. This is the average time it takes for the first ripe fruit to develop in ideal heat conditions. Magic Bullet, Pink Berkely Tie Dye, and Costoluto Genovese are considered mid-range, requiring 70 to 80 days to mature. The others are late maturers, needing more than 80 days to produce ripe fruit. Bicolor Marvel Stripe takes 95 days to mature. In cool areas of Marin, there may not be enough warm days for some late maturing tomato varieties to reach full production.

Click here for more advice on selecting and growing tomatoes. 

Herbs may not be the stars in the Edible Demonstration Garden, but they are notable members of the supporting cast. It’s hard to imagine a flourishing vegetable garden without a few culinary herbs as companions.

The supporting cast of herbs in the Edible Demo Garden includes basil, oregano, thyme, lemon verbena, chives, Mexican tarragon, anise hyssop, chocolate mint, lavender, pineapple sage, and rosemary. Some are harvested and sold fresh at the Indian Valley Organic Farm and Garden farm stand and others are dried and offered as seasonings and teas. They are among the most reliable plants in the garden.

What is an Herb?

The word “herb” can be applied to any non-woody plant with leaves, seeds, or flowers used for seasoning, medicine, or fragrance. It’s the culinary uses that most commonly interest home gardeners. Herbs are considered different from spices based on the part of the plant that is used. Spices are derived from the roots, bark, fruit, berries, and seeds of plants. Some plants can be both an herb and a spice. Coriandrum sativum, also known as Chinese parsley, is called cilantro when the green leaves are used as an herb and coriander when the seeds are used as a spice.

Why Grow Herbs?

Herbs are among the most satisfying plants to grow. Most are not fussy and can tolerate less than ideal garden environments. Many familiar herbs like sage, oregano, and rosemary are native to Mediterranean areas where the climate is similar to that in the Bay Area and therefore, they grow well in Marin gardens. There are many other good reasons for growing herbs.

• Herbs make good neighbors with other plants and can be easily integrated into both edible and landscape gardens. They are attractive enough to do double duty as ornamentals.
• Herbs are cost-effective. They are inexpensive to grow and can be harvested in the amounts required for a recipe. No need to spend money at the supermarket on packages of herbs.
• The blossoms on herbs attract pollinators and other beneficial insects.
• Herbs are usually not bothered by pests and diseases. Some herbs have been shown to repel pests affecting companion plants. An example is the ability of basil to deter thrips from invading tomato plants.
• Deer usually leave herbs alone, especially those with strong tastes and scents.
• Herbs grow well in containers and are a good choice when garden space is limited.

Tips on Growing Herbs

Most herbs thrive in full sun and well-drained soil, but many can be grown successfully in a range of conditions. Annual and biennial herbs such as basil, parsley, and cilantro have moisture and nutrient needs similar to those of other annual edibles and integrate well into vegetable gardens. Although perennial herbs like oregano, thyme, and sage require some regular watering, they are drought-tolerant and need little additional fertilization. They do well in more permanent locations or grouped together in an herb garden.

Some herbs are started from seed while others are easy to grow from cuttings. Information on the growing needs of common edible herbs can be found at http://marinmg.ucanr.edu/EDIBLES/EDIBLES_GROW_SHEETS/

Check the upcoming events listings on this website to register for a hands-on public workshop on growing and using popular edible herbs. There will be a workshop held on the College of Marin Indian Valley Campus on November 2, 2024, from 10:00 am to 12:00 pm.