Growing Strawberries

The plants are low growing perennials and provide a delicious supply of fruit either in June (from the appropriately named "June bearers") or throughout the summer (from day-neutral types). Plants fruit well in rows, beds, or even in pots, and make an attractive groundcover when not fruiting.

The strawberry plant is in many ways unique. It is an herbaceous perennial, composed of leaves, a crown (a compressed, modified stem), and a root system. In heavier soils such as clay loams, 90 percent of the roots can be located in the top 6 inches of soil. This shallow root system is, in part, responsible for the strawberry plant's sensitivity to water deficit and excess. Runners, or stolons, arise from buds at the base (axils) of the leaves; they are the strawberry plant's device for vegetative propagation.

Variety Selection

Because strawberry varieties are extremely sensitive to local conditions, a variety that performs well in one location may do poorly in another area. Varieties that perform satisfactorily in northern Pennsylvania might fail miserably in the southern portion.

Because of these differences in variety performance, gardeners are strongly advised to trial a number of varieties. Varieties with resistance to red stele and verticillium wilt are highly recommended.

June-bearing Strawberries

The strawberry most commonly grown in Pennsylvania is the June-bearing strawberry. The varieties we have now are the result of decades of breeding for productivity, size, and other attributes. These varieties are rated as early, midseason, or late according to when they bear.  Early varieties may be more subject to frost injury because they bloom earlier, and the opened blossom is the stage most susceptible to frost injury. 

Day-neutral Strawberries

Day-neutral strawberry varieties bear throughout the growing season. They are highly productive and flavorful. Day-neutral plants produce fruit in flushes where there are peaks and valleys in the number of fruit ripening at any one time throughout the summer. Day-neutral strawberries are not fond of very hot temperatures and may take a short break from fruiting in mid-summer.  The high-temperature effects can be ameliorated by a heavy straw mulch to keep soil temperatures low; however, even with this precaution, day-neutral varieties may not perform well in the southern half of Pennsylvania. Cultural practices for these berries differ from those of June bearers.

Planting

Keep plants in a shady area or refrigerator until planting, or better yet, if you've ordered your plants from a nursery, ask them to keep the plants until you are ready to plant. Place the roots in water about 1/2 hour prior to planting. Do not allow the roots to dry out during the planting process.

Strawberries should be planted in April and early May, as soon as the soil is in good condition--well worked, without excess moisture. Planting after June 1 is not recommended, but if it must be done, take extra care to keep the plants well-watered.

Plant June-bearing strawberries 18 to 24 inches apart in rows at least 36 inches apart with the soil line above the roots but not covering the growing point of the crown.  Way-neutral plants should be mulched immediately since they are sensitive to warm soil temperatures. Mulch with about 4 inches of clean straw. Flower buds of June-bearing strawberries should be removed manually in the first year to avoid flowering and fruiting stress on the young plant. Removing flowers allows the plants to direct their energy into root-system establishment and the development of a healthy, large leaf canopy that will "fuel" the next year's crop. Flower buds and runners on the day-neutrals should be removed only through early July of the first year and plants should be allowed to fruit after this date. The importance of establishing a healthy stand of plants cannot be overemphasized. Optimal soil moisture levels need to be maintained throughout the season so that plants become well established.

Nutritional Requirements

Conduct a soil test before planting.   Fertilizer amounts are listed below as general rules-of-thumb, but if the amounts may need to be reduced if you are growing your plants in a rich garden soil amended with compost. 

Apply 2 pounds of 10-10-10 per 100 feet of row after planting and an additional 2 pounds in late August.

Day-neutral varieties should receive a more constant nitrogen rate through the planting year. Apply 1 pound of ammonium nitrate per 100 feet of row once a month from June through the first day of September. Strawberry size can be increased dramatically by timely irrigation as the berry enlarges, but don't overdo it, since too much water will dilute the flavor of the berry.

Overwintering

Strawberry plantings require mulching for protection from the cold and soil heaving that can result from fluctuations in temperature.

Approximately 4 inches of clean (weed-free) wheat, oat, or rye straw or salt marsh hay should be applied in December. Do not apply mulch in clumps because this can smother plants. Mulch should be removed in spring, usually from mid-March to early April, after the danger of freezing is past but before much leaf yellowing occurs. Straw should be left in the rows as a bed for the berries to ripen on.

Renovation

June-bearing strawberry beds can be renovated and maintained for several years. Renovation thins the beds and invigorates the remaining plants. Plant thinning is essential because beds that retain too many plants yield small berries that are difficult to find under the dense foliage.

The renovation process should begin immediately after the harvest is completed. This gives the plants time to develop the canopy, which in the fall will determine the number and quality of flower buds that will produce fruit the following spring.

To renovate, remove weeds, narrow the rows to 6 to 12 inches, and thin the plants so that there is a plant about every 3 to 4 inches. Try to select strong runner (daughter) plants, and remove mother plants when they are 3 to 4 years old, replacing them with strong runner plants. Clip or mow the leaves off and fertilize the plants with about 5 pounds of 10-10-10 per 100 feet of row. Irrigate if the weather is exceptionally dry.

Renovation is not recommended for day-neutral strawberries. These plants will need to be replaced every third year.

With proper renovation and pest control each year, a strawberry planting should produce abundant large berries for at least 5 years.

Strawberry Plasticulture

Strawberry plants can also be grown on raised beds covered with black plastic. When black plastic is used, planting stock can be either dormant plants or plants grown from rooted runner tips (called plug plants).

With this system, trickle tape under the plastic for irrigation and row covers (lightweight spun-bonded material) for winter protection will also be needed. Plants should be grown in a protected location.

Plug plants are planted through the plastic in late summer or early fall; dormant plants are planted in July. Plants are spaced more closely than usual at about one foot apart in staggered double rows. Row covers are placed over the beds in mid-October to increase fall growth, and runners produced during the fall should be pinched off. Bloom and harvest begins earlier than usual in the spring since the soil will warm more quickly.  This means that frost damage is of greater concern.

About 1.5 pounds of 10-10-10 fertilizer per 100 square feet should be worked into the bed prior to planting. After planting, water-soluble fertilizers need to be used since granular fertilizers cannot be applied with the plastic in place. Three ounces of a 20-20-20 water-soluble fertilizer per 100 feet of row should be applied in the spring in each of three applications (9 ounces total) a week apart, starting when the plants make good growth. Dilute the fertilizer according to package directions to avoid burning the plants. Decrease or omit fertilizer applications if growth is overly vigorous.

Plantings can be kept for a second year of harvest. After the fruit production ends for the season, trim off the plants as close to the plastic as possible and allow them to regrow. Keep the plants watered and fertilize them with 9 ounces of 20-20-20 soluble fertilizer in late August, again decreasing amounts if growth is very vigorous.

Day-neutral varieties can also be grown on plastic, but white plastic should be used to keep soil temperatures from getting too hot.  Work the same amount of fertilizer into the area as for June-bearers above.  A light amount of fertilizer, only about 3/4 ounce of a 20-20-20 soluble fertilizer per 100 feet of row, should be applied weekly through the drip tape.

Harvest and Post Harvest Care

Berries are generally ripe 28 to 30 days after full bloom. Pick the berries after the plants have dried in the morning, and keep the picked berries out of direct sunlight. Pick when the berries are fully colored, retaining the caps. Refrigerate the strawberries as soon as possible. Do not wash the berries until just prior to use.