Warming weather often carries with it the delightful experience of fresh-from-the-garden berries. Strawberries, blueberries, blackberries, raspberries and currants are all easy to grow in the Bay Area.
Botanically, berries are the fruit (pericarp) produced by a single ovary. By this definition, cucumbers, eggplants, tomatoes, avocados, bananas and grapes are all types of berries, while strawberries and raspberries are not! Weird, right? Strawberries and raspberries are actually what is known as aggregate fruits. But don’t worry, today we will stick with learning about the fruits we more commonly call berries. (The British call them soft fruits because they do not have pits.)
Plants that produce berries are called baccate or bacciferous. Most berries are sweet and delicious, but not all of them. Potato flowers produce berries, but don’t eat them - they’re poisonous! Elderberries and mulberries are fine to eat when ripe, but poisonous when unripe. Now, people have been eating berries for as long as we have existed, but we’ve only been cultivating them for a few hundred years, so there’s probably a lot more to learn. We’ll start with the basics.
Generally speaking, all berries are shallow-rooted plants that prefer southern or western exposure. They do best in loose soil, so you can help berry plants by working a lot of compost into our heavy clay before planting, especially for blueberries. Soil compaction will seriously interfere with berry production. The use of deep-rooted cover crops, such as hairy vetch, marigolds, mustard, or rye will loosen the soil, add nutrients, and reduce erosion in berry plantings.
Berries do well in raised beds and they prefer soil with a pH of 6.2-6.8 (slightly acidic). Our soil tends to be more alkaline, and our water supply is very alkaline, so regular treatments may be necessary. Over-the-counter pH tests are only marginally useful. I urge you to get your soil tested regularly by a local soil test lab every 3 -5 years.
Most berries are susceptible to verticillium wilt and other fungal diseases. Crops should be rotated every 5 years to interrupt the pathogens’ life cycle. Commercial berry growers regularly fumigate with methyl bromide to combat black root rot. Methyl bromide is an ozone-depleting chemical that has been phased out of use in most other countries. You can help harvested berries last 30% longer by storing them in the refrigerator and only washing them just before eating.
People started cultivating strawberries commercially in the late 18th century. The Romans thought its wild cousin had medicinal uses due to the heart-shaped berry. Strawberries require an accumulation of 200-300 hours of temperatures between 32-50 °F to break dormancy. These are call chill hours. Strawberry flowers look hermaphroditic but they function as either male or female. New plants can be propagated using runners. If you want fruit, remove the runners. Like potatoes, strawberries are especially well suited to planting in towers. Powdery mildew, leaf spot, and leaf blight are common diseases, and pests include fruit flies, slugs, moths, thrips, weevils, mites and aphids.
Did you know that blueberries were not domesticated until 1911? Unlike strawberries, most blueberry species need 650-850 chill hours. What this means in the Bay area is, if we have an extremely mild winter, blueberry bushes may not know what to do with themselves. Blueberries love acidic soil. They perform best in soil with a pH of 4.2-4.8! You can acidify soil by adding sulphur or cottonseed meal. Be sure to follow package directions when adding sulphur. I used to lay pine boughs around my blueberry bushes, until I learned that that does not work. According to researchers at Cornell University, nitrate-based fertilizers can be toxic to blueberries.
Blackberries and raspberries are close cousins. Due to color variations, sometimes the only way to tell the difference is to pick them. If the torus (receptacle stem) stays with the fruit, it’s a raspberry, if it separates from the fruit, it’s a blackberry. Both varieties are called bramble fruits or caneberries, because the fruit is produced on bristly canes each year. First year canes (primocanes) produce palmately compound leaves and no flowers. Second year canes (floricanes) do not get longer. Instead, they produce lateral buds with 3-5 leaflets. At the ends of these lateral buds, fruit is produced on short stems called racemes. These members of the Rubus genus don’t seem to care what type of soil they are in. The most common problem with Rubus plants is insufficient pollination. You can improve the odds of pollination by installing plants that attract pollinators.
Keep in mind, every time the tip of a cane reaches the ground, a new plant will start to grow, so it is important to trellis these berries, unless you want an impenetrable bramble patch! Birds, caterpillars, aphids, weevils and beetles are the biggest pests. Anthracnose cankers can be treated with Bordeaux mixture (lime, water and copper sulfate). Raspberries should not be planted where peppers, eggplants, tomatoes, bulbs, or potatoes have been grown. These plants are often hosts for verticillium wilt, which can stay in the soil for many years. Traditional folklore says you should not harvest blackberries after Old Michaelmas Day (October 11th), because the devil has spit on them. Though it sounds funny, the truth behind the fiction is that cooler wet weather can cause certain molds to start growing on the fruit and may make it toxic. Once established, blackberries and raspberries (right) will come back, year after year.
I haven’t tried growing currants (yet), but they do well in the Bay area and the fruit is delicious. There are three basic varieties of edible currants: blackcurrant, redcurrant, and white currant. They, along with gooseberries, are members of the Ribes genus. Despite the name, these fruits are not related to the dried currants used in baking; those are a type of grape. If you want to grow currant berries, you can’t live in New Hampshire, North Carolina, or West Virginia. If you live in Massachusetts, New Jersey, Rhode Island, or Delaware, you’ll need a permit. These bans are in place because Ribes can carry White Pine Blister, an imported Asian rust fungus that has devastated high elevation pine forests. Currants generally prefer cool, well-drained soil, in partial shade or full sun. In our warmer climate, they prefer heavy soil (yay!) and partial shade. They can be grown as either shrubs or trees. Fruit is borne on spurs of 2- and 3-year old wood. Pests include aphids, spider mites, imported currantworms, and currant borers. Currants need a lot of potassium, but they are sensitive to potassium chloride, a common ingredient in fertilizer.
Which berries do you grow?
I hope this information inspires you to grow more of your own food. You can ask your garden questions on my Home page.