Strawberries are one of the most common fruits cultivated by home gardeners. They are one of the easiest fruits to grow and can be productive and economical producers.
There are three main types of strawberries, June or spring bearing, everbearing and day neutral. The largest fruit generally comes from June barring varieties. June bearing varieties produce one crop over a two-to-three week period in the spring and may be classified as early, mid and late varieties. Everbearing plants have three harvest periods during the spring, summer and fall and day neutral varieties can produce throughout the growing season. Everbearing and day neutral do not send out as many runners as June bearing varieties. If they are available for your area, day neutral are the most commonly cultivated and are generally preferable to everbearing varieties for fruit quality.
The best way to make sure you are getting varieties suited to your climate is to start with plants from a reputable local nursery center. They may only have a few varieties, but you are better off starting with plants you know are suited for your climate.
Generally strawberries are planted in the spring as soon as soil can be worked, but may be planted in the fall in warm climates. When days are long and temperatures warm, growth of leaves and runners will be stimulated. Cooler temperatures and shorter days will stimulate flower production. Temperatures can override day length for triggering flowering. Temperatures below 60F and above 80F will result in both poor vegetative growth and fruit production. For indoor growers who can control temperatures, the best results and flavor can be achieved by providing a differential between day and night temperatures of 70-80F day and 60-65F night.
Full sun at least six to eight hours a day is ideal for the highest yields. It is important to select a location where tomatoes, potatoes, peppers or eggplant have not been grown for several years. This helps to avoid Verticillium wilt which is a serious strawberry disease.
Strawberries prefer well drained sandy loam with a pH of 5.8-6.2. If possible a sloping site works well because it allows excess water to better drain away from the plants. A sloping site also lessens potential for frost damage by allowing cold air to drain away from plants. Amend soil with 1-2 inches of organic matter, preferably compost, or well-rotted manure.
Consider working some alfalfa meal into the soil to improve fertility and organic content.
Strawberry roots dry out very quickly. Be sure to keep the roots moist while planting or plants will not live up to expectations. When planting strawberries, it is very important to avoid burying the crown too deep. This will cause all sorts of problems and generally the crown will rot and the plant will die.
A great method for planting strawberries is to dig a large hole and then produce a mound in the center of the hole. Carefully spread out the roots over the mound, placing the crown at soil level. Back fill the hole and make sure the soil goes no higher than half way up the crown. Plants can be grown in raised beds, rows or containers with a requirement for spacing of six inches on all sides of each plant. If a large area is planted, care should be taken to leave space between rows for walking and tending plants.
Every gardener seems to end up with a “strawberry pot” sooner or later. These pots with a planting area on top and smaller receptacles on the sides for planting runners seem like a good idea. In reality they really are not optimal for strawberry growing. They are generally too small and hard to water consistently. With containers, bigger is generally better so to with 12” containers or larger. Strawberries have shallow roots so only six to eight inches of depth is needed, but small pots tend to heat up more than larger pots when exposed to full sun.
Consider placing slightly smaller plastic pots inside larger decorative pots and fill the space between the two with straw or mulch to help keep the roots cool.
A top dressing of mulch helps to hold moisture, cool the soil and keep weeds from competing with your strawberry plants. Mulch also helps to keep fruit and leaves out of the soil. If it is available straw works well. It is slow to decompose and dries quickly. Do not use hay, as it carries many seeds that will eventually germinate and cause problems.
Place a few layers of newspaper on the ground and water well before mulching. This will help keep weeds away, and as the paper decomposes it will feed beneficial microorganisms and worms adding organic matter to the soil. Some growers like to use weed block material for growing strawberries in areas where weeds are prevalent; but if this option is chosen, make sure that it is the breathable mesh variety. Do not use black plastic, as it will heat the soil, and cool roots are needed for fruit production. In colder climates, strawberries can be overwintered by covering plants with six inches of straw mulch to protect plants from freezing.
Regular tending of the crop can help prevent disease and pest problems. Remove brown, dry or discolored leaves and old berries. These can provide a host to fungal and bacterial disease and reduce air flow to the plants. Bottom leaves touching the ground can also be removed and additional mulch applied as needed. Remember that birds love fresh strawberries. Use bird netting, for outdoor plants, or make sure to plant extra for the birds.
Some growers prefer to pinch off flowers and runners for the entire first year on June bearing varieties and beginning flowers and runners on everbearing and day neutral varieties. There are two reasons to consider this practice. By pinching the early flowers and runners, you will encourage foliage growth and vigorous healthy plants that will be better producers in the long run. Pinching early flowers also encourages runners that can be used to increase the crop.
If you start with rich organic soil amended with well-rotted manure and compost that may be enough to get your plants off to a great start. Balanced fertilizer may be added at a rate of one pound per 100 sq. ft. worked to a depth of eight inches and watered in well before planting.
Avoid over fertilizing strawberries which can result in excessive leaf growth and poor fruit production. Also, take care not to fertilize late in the season in cold climates to prevent growth that will be damaged by frost. For day neutrals and everbearing varieties, fertilize liberally after each harvest. June bearers can be fertilized at the beginning of each growing season and again after harvest.
Strawberry plants have shallow roots and need to be watered often. They prefer consistently moist, but not soggy soil. Drip irrigation placed under mulch is generally the best option to provide consistent watering.
Other than a light feeding after each harvest, day neutrals and everbearing varieties don’t need special attention except for over mulching in colder climates in the winter. June bearing varieties should have the leaves cut to within one inch from the crown after harvest in addition to liberal feeding. An additional consideration for all varieties is to consider replacing mother plants with fresh starts from runners. As a general rule plants can produce well for three years under good conditions, but if production seems to be slowing down with each successive harvest, it may be better to go with some fresh starts. Some growers treat the plants as annuals starting with new plants each year.
The benefit of runners is that they allow for perpetuation and expansion of the crop. When growing in soil, the runners should be gently pressed into the soil and held down with small rocks until roots form. Wait to do this until runners are long enough to allow at least six inches from the mother plant. The same thing can be done when growing in soil based or hydroponics containers by placing small rooting pots in appropriate positions.
Day-neutral types are most often used for harvesting runners. As adult plants, they will develop flowers irrespective of the day length, as long as they have received a sufficient chilling period. This is given to freshly dug runners for around six to twelve weeks. After harvesting runners, clean them of excess soil wrap them in plastic and place them in the refrigerator. After a period of at least six weeks, they can be planted out any time and may be kept in cold storage up to five months.
Each strawberry plant should produce around one quart of berries. Berries are generally ripe in about 30 days after bloom. Strawberries must be picked at full ripeness, as they cannot ripen once picked. Once the berries are fully red, only taste will tell when they are at their peak of flavor. Pick berries in the morning or evening when it is cool and refrigerate immediately. Strawberries store best in the ventilated containers that store bought berries come in, and no more than three or four layers deep. Wash just prior to serving.
Commercial growers have been attracted to growing strawberries hydroponically because stacked systems allow for much greater production per square foot of land and the fruit is much easier and faster to pick. Hobby growers may do well to consider stacked systems as well, particularly for areas where good light is available. Other options that can be used for strawberries are nutrient film technique (NFT), Aeroponics, or other media based flood and drain, ebb and flow or drip systems.
Strawberries can be susceptible to root rot if sufficient oxygen and draining are not provided. This may be harder to maintain in NFT systems as the plants develop root mass. As with soil grown strawberries, positioning of the crown is of paramount importance. Only the base of the crown should be in contact with media or nutrient solution.
When first starting cold stored runners in the hydroponic system, start with a low nutrient EC of around 0.5, the second week EC can be gradually increased and maintained at 1.8-2.4. Maintain pH at 5.5-5.8. Be on the lookout for any plants that fail to develop and remove them to avoid introducing rot disease into the system.
Nick Fraser is a Garden & Greenhouse contributing editor.