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Home  > Question of the Week

Question of the Week

Permalink What information can you give me on greenhouse strawberry production?


Answer: I am pleased to provide you with information on greenhouse strawberry production.

In North America, greenhouse production of horticulture crops has been somewhat limited primarily to tomatoes and greens. Many consumers in the northern part of the country can get fruits year round; however, they tend to be not freshly picked. In recent years the fruit market has taken popularity among growers and consumers. Rather than strawberries picked before peak harvest, it is possible to produce strawberries in the winter, in a greenhouse.

100 years ago, Liberty Hyde Bailey found success in forcing strawberries to grow in greenhouses. Since then, many varieties have been readily available and are more productive. Cornell University has identified some of the most productive and flavorful varieties today and have focused their research on getting them to fruit during the off season (Pritts, 2000). Tristar, a cultivar developed by Maryland, was found to produce the highest yields and was the most flavorful variety in a study conducted in 2000.

Many factors need to be addressed to successfully grow strawberries in a greenhouse. Overwintering, lighting, heating, fertilization, irrigation, pollination, and pest management are just a few.

In relation to overwintering, the study conducted by Cornell University planted strawberry crowns into 6 inch pots filled with peat, perlite, and vermiculite in May and June, and continued to grow them outdoors through November. Plants were then moved into the greenhouse or a cold frame at about 28-30 degrees Fahrenheit. At staggered intervals, plants were taken out of the cold frame about 12-12 weeks before fruit was desired. For adequate establishment, the plants were deflowered and de-runnered for the first two weeks in the greenhouse.

Because much of North America is cloudy during the winter, supplemental lighting is required at night to provide additional day length. In trials performed at Cornell, supplemental lighting was provided from 2200 to 700 hours (10:00 P.M. to 7:00 A.M.) with high pressure 400 W sodium lamps. Since strawberries prefer lower temperatures than most plants, heating of the greenhouse is required only at night and heat from the lamps is adequate to produce the high temperatures during the day. The day/night temperature recommended by Cornell is 75/55 F.

Greenhouse production of strawberries has successfully done by both hydroponic systems and in a soil culture. What Cornell found was that for soil culture, 50-100ppm N was adequate for strawberries. Additional boron might be required if leaf levels drop below 30 ppm. Phosphoric acid can also be added to maintain an optimum pH level of 5.8-6.5.

The other big issue when it comes to greenhouse strawberry production is pollination. Strawberry flowers require some type of assistance to move the pollen from the anthers to the stigma. Instead of using honey bees or performed the daunting task of hand pollination, bumble bees are used to provide pollination for the strawberry plants. Bumble bee hives are short-lived, and thus need replaced every 6-8 weeks. For more bumble bee information, refer to the list of vendors provided below.

If bees are used for pollination, pesticides are not recommended to control the number of greenhouse pests such as fungus gnats, two-spotted spider mites, aphids, thrips, powdery mildew, and gray mold. Instead, biological control agents are introduced into the greenhouse before a pest outbreak begins. Therefore, it is essential to scout for pests and secure an efficient mode of action.


Jett, Lewis W. 2006. Growing Strawberries in High Tunnels in Missouri.

Pritts, M. 2000. Berried Treasures: Off-Season Production of Strawberries and Raspberries. Department of Horticulture. Cornell University.

Vendors Who Import them from Holland or Canada
GB Systems
P.O. Box 19497
Boulder, CO 80308
GB Systems
P.O. Box 300
Locke, NY 13092

The Green Spot
93 Priest Rd.
Nottingham, NH 03290



Permalink What information can you give me on growing dahlias for cut flowers?


Answer: Dahlias are currently among the most popular and best selling cut flowers. They can be grown from tubers or cuttings and are very productive; they bloom in northwest Arkansas from late June until frost.

Dahlias come in many shapes, sizes, and colors. A relatively new series called Karma dahlias were bred especially for cut flowers. You can see photos of many of them at the website and These companies sell tubers. You can also purchase Karma dahlias as rooted or unrooted cuttings from Germania or Gloeckner. They are grown in the U.S. by Bosgraaf, The rooted cuttings are less expensive than tubers, but you have to buy lots of them.

Last year I purchased some dahlia tubers from Banner Flower Farm in Michigan. Co-owner Patricia Banner was present at a specialty cut flower workshop in Memphis, Tennessee, that I attended in November. She has written an article on starting dahlias from cuttings that will be in the January issue of Growing for Market, and she will be giving a presentation on dahlias in November 2010 at the Association of Specialty Cut Flower Growers annual conference, which will be in Tulsa, Oklahoma. Several of her articles are referenced below. You can find more of her articles at the website as well as the descriptions and photos of varieties they sell.

Among the referenced articles, I think the one titled “Culture Profile: Dahlia” gives the most specific information about how to plant and manage dahlias. A few notes from my experience follow.

• Dahlias benefit from a heavy mulch of straw or leaves, and do not need to be dug up in the winter in Northwest Arkansas if they are well mulched.
• They need to be kept well watered in the summer. (They thrived with all the rain during the summer and fall of 2009.)
• They require strong support netting. I use Hortonova poly net, which I stretch horizontally over the bed about 2 ½ feet high. With the tallest varieties, a second layer of netting may be helpful. You can find sources for floral netting listed in the ATTRA publication
• Keep cutting the flowers! The longer I cut the stems, the longer they seem to grow.
• The plants and flowers look much better in the fall than they do in the heat of July and August.

You can find contact information for Gloeckner and Germania, sources for floral netting, and more in the ATTRA publication Specialty Cut Flower Production and Marketing.


Banner, Jim and Patricia. No date. Growing Dinner Plate Dahlias for Market; Maximizing Vase Life of Cut Dahlias; Early Blooming Field Planted Dahlias, Cooling, We’re Just Wild About Bouquets. Banner Flower Farm. 13 p. Online at

Schaafsma, Craig. 2002. Dahlias simplified: An expert tells how to grow them without much fuss. Growing for Market. p. 13-14.

Banner, Jim and Patricia. 2007. Growing dahlias: ‘These are your money makers.’ Growing for Market. p. 16—18.

Blount, Allison. 2004. An unsubtle love for dahlias. In Good Tilth. p. 13.

DeVault, Melanie. 2004. Good Karma—Dahlias that is. The New Farm. 5 p.

Preston, Bill. Culture profile: Dahlias. The Cut Flower Quarterly. p. 6-7.



Permalink What are some sources of information on building a walk-in cooler?


Answer: Thank you for contacting ATTRA with your request for information on how to build a walk in cooler.

Lynn Byczynski, in her recent book Market Farming Success, has a good section on coolers. Byczynski and her husband were market gardeners for over 20 years. She also has visited many other market growers as she collects material for her monthly journal Growing for Market ( Her comments are based on experience. Byczynski highly recommends purchasing a used cooler in good condition over a farm-built one. Secondhand coolers can sometimes be purchased from a florist going out of business, or a heating and cooling contractor who services coolers. You can also purchase a used cooler from Barr, Inc., a company that specializes in reconditioned refrigeration (; 920-231-1711).

That said you can find plans online for building your own. A few options are given below.

The most affordable option seems to be a device called the “Coolbot.” It is basically an adaptor that converts an air-conditioner into a walk-in cooler compressor. This system was invented on a farm and has been tested and affirmed as an affordable cooler alternative on a number of small-scale farms. Go to

The ATTRA publication, Post-Harvest Handling of Fruits and Vegetables, gives rudimentary plans for a “Portacooler,” a portable precooler designed by USDA researchers can be built with readily available materials. The Portacooler can be towed to the field and used to reduce field heat of berries, vegetables, and other high-value crops immediately after picking. It is not intended for long-term storage. Please check these websites: and
A 3-page bulletin, Walk-In Cooler by D.E. Darby, can be found at It gives information on building one. Finally, you should check for a discussion among other market gardeners about their experiences.



Permalink What are some resources on using corn gluten meal for weed management?


Answer: Thank you for your contacting ATTRA, the National Sustainable Agriculture Information Service, for information about corn gluten meal for weed management.

The herbicidal qualities of corn gluten meal were discovered accidentally by Dr. Nick Christians, an Iowa State University professor whose specialty is turf. Dr. Christians maintains a website with information about the use of corn gluten meal, sources of the product, and more. Please refer to the following resources for more information.


Christians, Nick. Corn Gluten Meal Research Page. Iowa State University of Science and Technology.

Christians, Nick. How to use corn gluten meal. Iowa State University of Science and Technology.

Powell, Kathy. No date. Corn Gluten Meal: A Natural Herbicide. University of Wisconsin Urban Horticulture.



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