Cover Crops & Soil Enhancement

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.

After an especially busy summer and fall harvest season, it was time to consider what to plant next in the Edible Demo Garden. In Marin it’s possible to grow vegetables year-round and there are plenty of winter crops such as cabbage, cauliflower, and onions to select. However, another option is to not plant anything during the winter months and give the garden beds some time to rest and rejuvenate. This puts the focus on caring for the soil so that when it comes time for spring planting, the garden will be ready. With this plan in mind, the recent off-season activities for the Edible Demo Garden volunteers have concentrated on methods for giving the garden time to rest. The primary options for resting the garden are planting cover crops and allowing some beds to be fallow for a season.

Planting cover crops

There are many advantages to planting cover crops. Cover crops, sometimes referred to as “green manure”, are an excellent way to protect and improve soil. They increase organic matter, suppress weeds, prevent damage from wind and water erosion, and support beneficial insects and earthworms. Plus, they can look attractive while nurturing the garden.

Cover crops are divided into two main categories: legumes, such as clover and fava beans, and non-legumes, like rye and buckwheat. Legumes have the added benefit of fixing nitrogen by taking it from the air and converting it into a form to be used by plants. Cover crops are turned over when they start to flower and allowed to decompose prior to spring planting.

Two different cover crops were chosen for the Edible Demo Garden. Fava beans were planted in several of the garden beds and in the straw bales used for the summer crops. The latter is an experiment to determine if there is sufficient residual fertility in the straw bales to support another crop. In order to aid in germination and enhance their nitrogen fixing effects, the fava bean seeds were soaked in an inoculant containing rhizobacteria prior to planting. As an alternative cover crop, a green manure mix of bell beans, field peas, and purple/hairy vetch was planted in some of the raised beds. Past experience with crows eating the sprouting seeds necessitated the use of compost, straw, and protective netting to give the cover crop seedlings a fighting chance. The effectiveness of the different cover crops will be tested in spring when it is time to plant again.

Allowing beds to remain fallow

Taking a garden plot out of the crop rotation for a season can give the soil time to naturally replenish nutrients. It can also be a way to discourage pests, prompting them to move on once their food source is gone. However, fallow garden beds can also invite weeds and leave the soil exposed to the elements. In the Edible Demo Garden, layers of compost and straw were added to suppress weeds and protect the soil in the beds designated to be fallow. The winter rains will keep the soil moist and provide a habitat for earthworms and beneficial microbes.

Click here for more information on cover crops and soil enhancement in the off-season.

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.