Strawberries

History

Strawberries are a member of the Rosaceae family, also known as the rose family, which includes the ornamental rose, along with apples, almonds, blackberries, cherries, pears, and raspberries (see Figure 1). Members of this plant family include woody shrubs or trees, although strawberry plants are more herbaceous with a low-growing habit. Strawberry’s scientific name, Fragaria x ananassa, includes an “x” to indicate its hybrid nature — in this case, of two different species.

Wild strawberries have existed since ancient times, mentioned in Rome during the 1^st century A.D., but this crop was not commonly consumed due to the fruit’s small size and lack of flavor. The wild wood strawberry (Fragaria vesca) and musky strawberry (Fragaria moschata) were both cultivated in Europe during the 1300s to 1500s. Garden strawberries were developed from a cross between a native North American strawberry (Fragaria virginiana) that is flavorful and productive, though small, and a native Chilean strawberry (Fragaria chiloensis) that is larger in size. F. virginiana and F. chiloensis were transported to France in 1624 and 1712, respectively. An accidental cross between these two species in a French garden produced large, productive fruits grown on vigorous plants, and the garden strawberry (Fragaria x ananassa) was born. The English are responsible for continuing the breeding effort and creating the modern garden strawberry, and by 1800 this crop was transported back to North America (see Figure 2). By 1825 strawberries were being grown in the U.S. and breeders worked to improve fruit quality and productivity.

The red strawberry fruit we call the “berry” is an enlarged flower stem (or receptacle) with many seeds embedded in the surface (Figure 3). What looks like seeds on the berry (referred to as achenes) are really the “true fruits” (Figure 3). Inside the dry ovary of each achene is a real seed (ovule) with the potential of becoming a unique strawberry plant (seedling) (Figure 3). Like most hybrids, the offspring usually does not preserve the horticultural characteristics of the parent strawberry. To preserve strawberry varieties that yield superior fruit, strawberry propagation is generally accomplished by rooting runner plants that are identical in genetic makeup to the mother plant.

Varieties

Strawberries are a warm season crop with varieties that can be grouped into (1) short-day (sometimes called “June-bearing”), (2) everbearing, and (3) day-neutral. Temperatures between 50-80 degrees F and a day length of 14 hours or less is required for development of flowers and fruit for most varieties. Fruit production is not constant but occurs in cycles that can be interrupted by freezing weather. Strawberry plants have complete flowers, with both male and female parts, and adequate pollination is vital for fruit set and proper development.

In Louisiana, short-day varieties are most commonly planted in early October through mid-November, and will start bearing fruit in the winter, continuing until peak production in the spring. For Louisiana and other southern states with a warm climate, fruit production usually occurs from late February to May. Fruiting is initiated during the shorter days and cooler temperatures of winter (hence the name short-day). Short-day varieties are more popular in Louisiana as they produce fruit during months when weather conditions make strawberries less susceptible to disease (less humid and hot).

Everbearing varieties begin flowering during 12-hour days, while day-neutral varieties are not influenced by length of days (hence the name day-neutral). Everbearing and day-neutral varieties can continuously bear fruit until a hard frost but fruiting is usually curtailed by high temperatures (above 90 degrees F), making them less ideal for growing in Louisiana.

It is recommended to select disease-resistant varieties whenever possible. See the recommended strawberry varieties for Louisiana in Table 1.

Table 1. Recommended Strawberry Varieties for Louisiana

When and How to Plant

It is recommended to start with bare-root strawberry plants or plugs (containerized transplants) in a growing state with a good root system and leaves. It is important to purchase disease-free plants and varieties that are best suited to your area. Plants can be stored under refrigeration, loosely wrapped in plastic until transplanting outdoors. Bare-root plants are the most common type of strawberry plant available at garden centers or farm stores. These plants may or may not have leaves on them. Those that have leaves on them at the time of transplanting generally produce greater, earlier fruit than those without leaves. Bare-root transplants require frequent sprinkler irrigation during the heat of the day for the first 1 to 2 weeks after transplanting. Plug transplants require less irrigation after transplanting as the root system generally stays intact when the plant is pulled from the container.

Refer to the Strawberry Planting Guide (Table 2) for the recommended dates to plant strawberry bare-root plants/plugs outside. The optimum growing temperature for strawberries is 70-75 degrees F. They should continue growing, blooming, and setting fruit until the end of the spring for short-day varieties or until a hard frost for everbearing or day-neutral varieties. For everbearing and day-neutral varieties, fruit production will slow or stop during temperatures above 90 degrees F.

It is recommended to plant strawberries in double-set rows (i.e., 2 rows per bed, 12-14 inches apart) for increased yield (see Figure 4). At the recommended spacing, strawberry plants/plugs should be set deep enough into the ground so that the roots are positioned straight down into the soil (not bent) and the bud and crown of the plant are placed just above the soil line. It is important not to set the transplant too deep, covering the crown, or too shallow, leaving the roots exposed.

Table 2. STRAWBERRY PLANTING GUIDE

Where to Plant

Strawberry is a perennial warm season crop grown as an annual and prefers well drained, sandy soil and full sun (at least 6 hours/day). It doesn’t tolerate heavy clay soil. Strawberry plants grow well in a soil pH between 5.2 and 6.2, but growth is optimized in a soil pH of 6.0-6.2. It is strongly recommended to plant strawberries in box beds or in traditional raised garden rows that are about 8-12 inches tall to ensure good drainage and prevent disease. If only growing a few plants, strawberries can be grown in containers that are at least 8 inches deep with drainage holes. In all types of gardens, it is recommended to add a 2- to 3-inch layer of compost, peat, rotted hay, or other organic matter and mix into the soil to optimize plant health.

Black plastic mulch — or a plastic fabric/film — is strongly recommended to increase soil temperature, yield, fruit size and quality, while controlling weeds and preventing fruit rot. Mulch is strongly recommended for strawberry plants; when fruit touches the soil, it will be prone to fruit rot. If plastic mulch is not used, place 4-6 inches of straw or pine mulch to create a barrier between the plants and the soil. It is recommended to use drip irrigation with plastic mulch to optimize yield and quality.

Early plantings may require row covers for protection depending on the weather and whether plants have acclimated to cool temperatures. Row covers or other coverings are recommended to protect strawberry plants from frost and to retain heat for earlier fruit production. Strawberry flowers and fruit can be damaged by air temperatures below 32 degrees F. Leaves and crowns of strawberry plants that have been acclimated to cool fall or winter weather do not sustain permanent damage unless exposed to air temperatures near 20 degrees F. In Louisiana, the most practical method for gardeners to protect flowers from freeze damage may be to cover plants with blankets, sheets, or frost cloth. Place the covers loosely over the plants and secure with staples, sand bags, or stones before the cold temperature event. Floating polypropylene row covers that are 1-2 ounces per square foot also work well. Protecting plants with coverings inhibits pollination, so remove during the day and re-cover at night. Using wire hoops every 10 feet under the row cover helps to keep the fabric directly off the plants (this is particularly important for flowering plants). A small “tunnel” may also be created using PVC hoops and clear plastic sheeting to create a greenhouse effect. Depending on the air temperature, the sides can be raised or lowered. For container-grown strawberry plants, move the containers into a garage, shed, or other enclosure during low temperatures.

Plant Care

Watering

Strawberries have a high demand for water and should be watered daily for a week or two after planting. Sufficient water is also critical during fruit production due to the shallow root system. Drip irrigation is very helpful to ensure consistent, adequate water for the long production season. Aim for 1 inch of water per week (rainfall and/or supplemental irrigation). Later in the season, with warmer weather and when the plants are larger, watering 2-3 times per week may be needed.

Fertilization

Although strawberries are grown as an annual in Louisiana, they may perennialize with good drainage, regular watering, and the addition of organic matter when preparing the bed. Organic matter feeds soil microbes which assist in gathering nutrients for plant roots. Small, malformed fruit may be due to calcium or boron deficiency but are just as likely to be caused by late frost injury. If fruit continues to be misshapen after the season warms, conduct a soil test and discuss results with a local county extension agent.

Organic fertilizers such as compost, fish emulsion, composted poultry litter or manure, worm castings, and blood or bone meal originate from living organisms. They are far more environmentally sustainable and safe than traditional synthetic fertilizers. They naturally release nutrients more slowly and over a longer period of time. When applying organic fertilizer, it is important to use in unison with compost, cover crops, and crop rotation, which all work together to build soil health. Learn how to convert inorganic fertilizer recommendations to organic fertilizers here.

Alternatively, a synthetic fertilizer may be used during bed preparation at the rate of 2 pounds (4 cups) of 13-13-13 for every 25 feet of row or 75 square feet. Broadcast or sprinkle evenly over the soil before transplanting and then mix in about 3-6 inches deep using a rake. Sidedress in early February and early April. Sidedressing is the addition of fertilizer to the soil around already established plants when the plant begins to fruit or vine, primarily to provide nitrogen. When using synthetic fertilizer, sprinkle a small amount lightly around each plant, keeping it several inches away from the plant stem; water into the soil. Because of their slow, steady release of nitrogen, crops fertilized with organic fertilizer do not usually need to be sidedressed, though fish emulsion is a good, quick-release organic source of nitrogen for sidedressing if leaf yellowing occurs.

Weeds

Plastic mulch will control most of the weed; hand-pull weeds close to the plant, especially those growing in the planting holes. It is important not to allow weeds to shade strawberry plants since they have a low, compact, sprawling habit.

Insect Pests and Diseases

Common strawberry insect pests include aphids, spider mites, and thrips, along with birds, snails, slugs, and worms. Strawberry plants are susceptible to foliar and fungal diseases (e.g., anthracnose, downy and powdery mildew, and leaf spot). Some strawberry varieties are more resistant to disease, and these should be selected and planted. Generally recommended tools for prevention are using mulch; avoiding overhead irrigation (except during plant establishment); adequate plant spacing; and weed control. See Table 3 to aid in diagnosis and management of some common strawberry insect pests and diseases.

Table 3. Organic and Natural Management for Common Strawberry Insect Pests and Diseases

Harvest and Storage

Strawberries should be harvested when fruit is red and ripe during the coolest part of the day, usually early morning. Ripe fruits are tender and bruise easily, so a gentle picking method and postharvest care are needed. To harvest strawberries without damaging the plant, pinch the stems (pedicels) to remove rather than pulling the fruit off. This should leave a short stem attached to the fruit, which also helps to minimize touching the fruit directly during processing. Another harvest method is to hold the fruit between thumb and forefinger and snap the fruit from the stem by twisting the forearm and wrist. Berries won’t continue to ripen after harvest. The fruit starts to deteriorate soon after it is totally red, so it is recommended to harvest fruit regularly, every 2 to 4 days.

During fruit production, strawberries may be harvested every few days for up to 6 months. Do not wash fruit until ready to eat as this will cause molding. After harvest, the crop needs to be cooled down to remove field heat and placed in a refrigerator or cooler where there is high humidity. Removing field heat will help prevent moisture loss and wilting and will preserve quality and shelf life. Strawberries should be placed in pint-sized plastic mesh baskets or clamshell containers and stored between 32-34 degrees F (95% humidity). If strawberries are not eaten immediately they should be placed in a refrigerator. Berries are very perishable so should be consumed within a week.

Preserve strawberries by freezing whole or sliced, or can into jellies and jams.

Strawberries are Nutritious and Good for You

Rich in Vitamin C

Important for bones, skin, blood vessels

High in Potassium

Essential for body function, especially the heart, kidney, nerves, bones, and muscles

Good source of dietary fiber

Important for bowel health, lowering cholesterol, controlling blood sugar, and maintaining a healthy weight

Recipes

Common methods of preparing Strawberries

Video on how to cut Strawberries

Guide to freezing and canning strawberries

Taste-testing ideas: strawberry smoothie, oatmeal with strawberries, strawberry s’mores, strawberry yogurt popsicles, strawberry pancakes, strawberry parfait, strawberry crepes

Other websites with many strawberry recipes:

USDA MyPlate Kitchen

Produce for Better Health Foundation

SNAP-Ed San Francisco

SNAP-Ed Arizona

Sources

• LSU AgCenter, Vegetable Gardening Tips: Strawberries
• LSU AgCenter, Louisiana Commercial Vegetable Production Recommendations
• UF Extension, Planting Guide
• UF Extension, Growing Strawberries in the Florida Home Garden
• UF Extension, Vegetable Production Handbook of Florida
• UGA Extension, Home Garden Strawberries
• Texas A&M AgriLife Extension, Production Guide for Texas-Grown Strawberries
• UMass Extension Vegetable Program: Disease, Insect, and Mites Fact Sheets
• Alabama A&M & Auburn Universities Extension, Crop Production
• University of Missouri, Integrated Pest Management, Strawberry: A Brief History
• University of Vermont Extension, History of the Strawberry
• Purdue Extension FoodLink: Strawberries
• University of Georgia Extension, How to Convert an Inorganic Fertilizer Recommendation to an Organic One, Circular 853