Wednesday, April 4, 2012

Strawberries in Containers

The strawberries we enjoy today result from a long history of selection and hybridization among several of the fifty-odd natural species. Everbearing (or day-neutral) strawberries produce a bumper crop in early summer, another smaller crop in late summer and a few berries here and there throughout the season in between. Because of the long harvest season, they are a good choice for home gardeners.
Regardless of the variety, strawberries grown in the ground must be relocated about every three to five years. The plants are subject to viral disease and pests that can reduce yields significantly. Many of these problems persist in old, dead foliage or in the soil. Regular renewal of the plants and their growing medium offers the best natural defense against these problems. In terms of standard crop rotation, strawberries should be separated by five years from soil that has previously grown any member of the potato family. This is because several important crop diseases are common to the two groups of plants.  Crop rotation can be a real problem for the backyard grower with limited space. In the case of strawberries, container growing offers a great alternative, since plants can be repotted in new, sterile growing mix every season or two.
Plant breeders have produced new lines of strawberries that are better suited to container cultivation than their traditional counterparts. Dutch hybridizers have produced varieties that not only bear luscious, tasty strawberries but also have large, showy flowers. This makes the plants decorative as well as productive. The variety shown in the photo at left is “Tristan.”
Strawberries need full sun and a well-drained sandy soil of slightly acidic pH, about 6.0-6.5. Any good commercial potting mix will work for strawberries, or you can make your own by mixing equal parts of sifted compost, horticultural peat and sand. Rainfall or irrigation should provide an inch or two of water per week during the growing season. Purchase certified disease-free plants in late winter or early spring, before they break dormancy. Although plants will grow and bloom in a small container, choose a pot that holds at least a gallon of growing medium for best results. Smaller containers may need watering more frequently than you would prefer.
I try to avoid the traditional “strawberry jar” (an urn with extra openings in the sides for planting) because they seldom hold enough soil to accommodate the roots of all the berry plants tucked into them. I also avoid hanging baskets, because I find they dry out too quickly and thus demand too much attention during the hot summer months.
Remove runners from container plants as they form. Allow the occasional runner to root in a small pot before detaching it, if you want to increase your stock of plants. Just set the crown of the runner on the soil. When it roots itself sufficiently to resist a gentle tug, cut it free.  Such plants will bear the following season, typically.
Feed everbearing strawberries regularly. Due to the repeated flushing of the container with water, nutrients will be lost. Watering with compost tea or a similar soluble fertilizer every other week will keep plants productive. Or use a timed-release fertilizer.
After the first frost sends plants into dormancy, remove any dead foliage and place the containers in a sheltered spot for the winter. Cover them with a blanket of pine needles or autumn leaves. You can wait until the plants break dormancy to return them to their sunny position on the porch or balcony, or you can bring a plant or two indoors in early January. Place the pots in the sunniest location available, protected from frost. This will allow you to harvest the first berries about a month to six weeks earlier than normal. We currently have berries ripening along with spring lettuce, allowing us to enjoy a delicious salad topped with freshly picked berries. See the accompanying photo of a plant forced as just described, taken yesterday. This plant, by the way, is growing beautifully in a nursery container holding only a half gallon of growing medium, demonstrating how well adapted to container culture this breeding line really is. The variety shown is "Loran." The fruits are slightly tart, and bursting with strawberry flavor. If you get too much rain while fruits are ripening, they tend to become watery. Another advantage to containers is that they can be moved out of the rain when needed, to avoid this problem. 
A well-grown plant in a roomy container can produce about one pound of fruit or more per season. Strawberries can be frozen or made into jam or preserves. Rich in vitamin C and phytochemicals, fresh strawberries can be added to salad or turned into a cold fruit soup (see the recipe below). They also star, of course, in desserts like strawberry shortcake.
Strawberry Soup
For 4 servings:
1 pint fresh strawberries, stemmed
2 cups apple or white grape juice
Juice of one small lemon
10 large, fresh mint leaves, plus small leaves for garnish
Salt (if desired)
Sugar (if desired)
Sour cream or yogurt to serve (if desired)
Reserve four perfect strawberries for garnishing the dish. Roughly chop the remaining strawberries and process in a food processor or blender, in batches if necessary, with the juices, the mint leaves and a pinch of salt, until you have a smooth puree. Chill until very cold. Taste and correct the seasoning with salt, lemon juice or sugar, as you deem necessary. Slice the reserved strawberries lengthwise, beginning at the pointed end, stopping before you completely cut through the stem end. Ladle the soup into chilled bowls. Place a dollop of sour cream or yogurt, if using, in the center. Fan out the berries gently and float one on each bowl of soup. Garnish with small mint leaves and serve.

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