By Eric Sideman, Ph.D.
I always have fresh cream at home from mid-June until mid-August. Berries are good with milk or yogurt, or plain, but they are best with cream. And the best berry? The one that is in season! For people who do not farm or garden, that season can be hard to determine, because almost every kind of berry is available almost any time of year in grocery stores. But some of us look forward to berries only in winter and eat them only in summer. For us, first come strawberries, followed by many others. Being first makes strawberries special, and I make sure I have cream on hand before they ripen.
I grow only June-bearing strawberries. Varieties called “ever bearers” will produce berries nearly to Thanksgiving, but by then I am onto something else. (By July I am onto blueberries.) If you farm, seasonal production may be important for you too. A farmer must consider marketing before growing a crop, and selling strawberries in June is very easy. All you need is a sign by the road. In the fall you can sell lots of strawberries, but you need a plan, since people looking at signs on the road then are looking for the words “apples” or “pumpkins.”
The typical way to grow June-bearing strawberries is to plant them in early spring the year before harvest. Getting it right from the start will yield much more success.
Site Selection and Preparation
Strawberries will grow on most soil types, but very sandy soil may lead to problems with drought; and poorly drained, heavy clay soils may lead to disease problems, such as red stele. Strawberries do best in soil that is high in organic matter and fertility; that is well-drained yet able to hold a continuous supply of moisture; and that has a pH of 5.7 to 6.
Air Drainage and Frost Protection
Ideally, a strawberry bed should be slightly higher than the surrounding land so that cold air will drain away to lower ground. A few feet of elevation often will be enough to protect delicate blossoms from a late spring frost, which will kill them. Strawberry blossoms can tolerate temperatures from 22 to 29 F. A frosted blossom will develop a dark center and will not produce fruit. So during blossom time the bed needs to be covered if a frost is predicted. Commercial growers should not attempt strawberry production without some means of frost protection. See the MOFGA fact sheet on growing organic strawberries for details. (https://www.mofga.org/wp-content/uploads/2021/01/FS 02 Strawberries web.pdf)
Preparing the Soil
Prepare soil well before strawberries are planted in order to build fertility, organic matter and soil structure, and to get rid of pests and weeds. Once strawberry plants send out runners and form the matted row, organic growers can control weeds only by pulling them by hand; so get a field as free of weeds as possible before strawberries are planted.
Insects, especially grubs that live happily under sod (larvae of June beetles, Japanese beetles and others), are another reason to prepare a field well before planting strawberries. Organic growers starve grubs by getting rid of sod at least a year before planting.
One could prepare sod ground for berries by this method:
1) Plow in late summer (a year and a half before planting berry plants).
2) Test soil and apply the recommended amount of lime.
3) Plant a winter cover crop in early September. Winter rye works well for growers with a tractor implement; annual ryegrass or oats, both of which are winterkilled, are recommended for growers working with a tiller or by hand.
4) The following spring, till in the fall cover crop and add recommended amounts of rock powders, such as Sul-Po-Mag for magnesium and potassium and rock phosphate for phosphorus. (See MOFGA Fact Sheet #1 for details on reading soil test results and meeting nutrient needs with natural amendments; and MOFGA Fact Sheet # 11 for natural sources of crop nutrients. Fact sheets are posted at https://www.mofga.org/Default.aspx?tabid=133.) Also, this is an ideal time to add manure. Common application rates are 5 to 8 tons per acre (about 35 lbs./100 square feet) of poultry or rabbit manure or 10 to 15 tons per acre (about 70 lbs./100 square feet) of cow manure. If you use poultry manure, use less lime and rock phosphate; layer manure will supply approximately 15 pounds of phosphorus per ton.
5) Plant another green manure crop or series of crops for the spring, summer and fall before planting berries. The choice of green manure depends on many factors, such as your major goal. Usually, when trying to condition sod ground for strawberry production, the primary concern is weed control. The following is a good plan in most cases:
a) Plant oats in spring.
b) Plow oats under in early summer. Plant sorghum-sudangrass if you use tractor implements; buckwheat if you use a tiller or turn by hand.
c) Plow the summer crop under in late August or very early September and plant a cover crop of oats for the fall and winter.
If your land is really weedy, be much more aggressive in getting rid of perennials such as quackgrass and depleting the seed bank of annual weeds. (See MOFGA Fact Sheet #10 on using a series of green manures alternating with fallow periods to control weeds. You must do this before you plant the berries.)
6) Plow under oats as early as possible in the spring, wait a few weeks, cultivate and plant the strawberries. Typically strawberries come as bare-rooted plants. Make sure you order these the winter before planting and have them delivered in early May.
The choice of strawberry varieties is based on taste, use of berry, winter hardiness, disease resistance and ripening date. Taste is always my primary factor. The University of Maine Cooperative Extension Bulletin #2184, “Strawberry Varieties for Maine,” describes most of the varieties suitable for New England and is available from your local Extension office and at https://extension.umaine.edu/publications/2184e/.
Strawberries should be planted early in the spring. Late spring plantings may have problems when hot, dry weather arrives, because they did not have time to develop adequate roots. Planting depth is extremely important: Crowns should be just level with the ground.
In the matted row planting system, still the most common and tried and true system, plants are set 18 to 24 inches apart in rows 4 feet apart. All runners are allowed to root, but beds are kept 18 to 24 inches wide by cutting off runners that extend into the alley; use a hand hoe, rolling coulter wheel, cultivator or rototiller. Keep these rows maintained over the years of your bed. The most common problem gardeners have is that all the rows grow together to form a solid bed of strawberries. This reduces yield, because the best production of berries is along the edges. More edges means more berries.
To ensure early runners and vigorous plants, remove all blossoms during the planting year. Failure to do this may result in weaker plants with lower yields.
For the most part fertility is established before planting and is based on soil testing. However, since June-bearing strawberries set buds for the following year’s fruit in the fall, adequate available fertility, especially of nitrogen (N), is crucial then. To get good bud set, N fertilizers are applied in mid to late summer before the bearing year, so that organic fertilizers have enough time to break down and become available by early fall. A common practice is to apply enough high-N materials, such as fish meal, seed meal or alfalfa meal, to supply 30 pounds of actual N per acre (2/3 of a pound of N per 1,000 square feet, which would be about 10 pounds of soybean meal). Compost can be used as a supplement and serves well to condition the soil and balance nutrients but does not provide enough available N at the time needed. An inch of compost and the appropriate amount of a high-N organic material spread directly over the rows is recommended.
Strawberries should be mulched over winter to protect the plants from extreme cold and, more importantly, from damage by rapid freezing and thawing of soil. Although threshed straw is the most commonly used mulch, any material that will provide protection without matting can be used. This includes marsh hay, sudangrass, pine needles or coarse wood shavings (not sawdust).
Apply mulch after 10 to 20 frosts, when the plants look pretty dormant, but before the temperature drops below 20 F. The exact time will vary from year to year and place to place. In central Maine, this is usually around the week before Thanksgiving.
Apply mulch 4 to 6 inches deep over the rows. This will take 100 to 150 bales of straw per acre.
Remove mulch as soon as possible in the spring by raking it into the aisles where it can retard weeds and conserve soil moisture. Many growers like to leave it on the plants somewhat longer to delay blossoming (beyond the danger of a late frost, they hope). This does work but has been shown to reduce total yield.
Renovate or Rotate?
Conventional growers renovate their fields after harvest. Within a week after harvest, they mow the old foliage to 1 inch above the crown and narrow the rows to 10 to 12 inches with a rotovator or tiller. This practice is questionable for organic growers, because without herbicides, weeds often compete better and take over when released from the shade of the old strawberry foliage. Organic growers may be better off not mowing and just narrowing the rows and fertilizing at this time.
Better yet, growers with enough land may profit most when strawberries are picked for only one or two years and then the berries are rotated to a new, prepared field. Growers have to decide what works best for them, but organic commercial growers will probably not be able to harvest for more than two years from a field before weed and pest management is lost. Gardeners have a good chance of maintaining a bed of strawberries longer, because managing weeds, insects and diseases in a garden is less daunting than on a farm.
For details about organic pest management in strawberries, see the MOFGA Fact Sheet at https://www.mofga.org/wp-content/uploads/2021/01/FS 02 Strawberries web.pdf.
Eric Sideman is MOFGA’s organic crop specialist. You can contact him at 207-560-4142 or [email protected].