Season Extension

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Season Extension

Fact Sheet:

  1. Season Extension



Ask an Organic Specialist: Season Extension Answers

I have been having problems with aphids in my high tunnels. What can I do to control them?

Answer by Organic Specialist Joe Pedretti: Greenhouses and high tunnels are great tools, but they also provide a nice protected environment for certain insect pests. Normally, aphids are kept in check by predators, parasites and by wind and rain which can knock them off plants. In the protected environment of a greenhouse or high tunnel, they can become a problem because there are few or no natural controls. In the right conditions, aphids and other pests, such as whiteflies and spider mites, can explode in numbers very quickly.

Aphids are sucking insects that weaken plants by sucking up sugars and other fluids from crops. They are not easy to see, since they are the same color as the plant stem and generally like to feed on stems, buds, and underneath leaves.

Step one for control is to monitor your crops on a regular basis. Infested plants are often stunted and can be a lighter green or yellow. Look closely at the stems under the leaves for aphids. A magnifying glass or loop can help. A good approach that saves time is to flag “sentinel” plants. Mark plants in a grid pattern and only monitor those specific plants on at least a weekly basis. If you find significant numbers of aphids on these plants, you know it is time for control options. Yellow sticky cards are another good monitoring device. Adult female aphids have wings and are strongly attracted to the color yellow, which mimics the color of sickly plants. The cards are coated in sticky glue, which traps them. Check cards at least weekly for signs of adult aphids. Sticky cards need to be replaced frequently to work well. Fortunately they are cheap and available through any greenhouse supply company.

If you have any infested plants in a greenhouse or high tunnel, you should begin control options since their numbers can explode quickly.

Here are your options as an organic farmer:

Biological control

There are a number of predators and parasites available for purchase and release. Ladybug larvae are the most familiar, but there are parasitic wasps, lacewings and others available now as well. Biological controls work best to keep aphid levels down, but may not give good control if you already have a problem. They simply cannot reproduce as quickly as aphids (which can actually reproduce without males- females give birth to clone daughters). Beneficial insects work best as preventative controls. A number of companies sell beneficial insects, including:

Non-Chemical Spray

Soapy water will kill aphids. The soap strips away their waxy cuticle and they die of dehydration. In order for this to work, they must be directly sprayed with the soapy water. Use a sprayer and mix one tablespoon of liquid soap per gallon of water. (Dr. Bronner’s is pure soap. Be careful not to use soaps with perfumes, dyes or other synthetic additives.) There are also many ready-to-use brands that are OMRI listed including the common Safer Insecticidal Soap.

Allowed Chemical Sprays

Remember that all insecticides approved for organic use are “restricted use” products. You can use them only when your other control options have failed, and you must notify your certifier if you intend to use a new product and the reason you must use it. Pyrethrum/pyrethrin-based sprays will work on aphids, but have a very short residual effect and must come in contact with the aphids. The product Pyganic works well, since it is pyrethrin mixed with oil, which coats and kills aphids and many other insects. Your certifier should be able to provide a list of approved pyrethrum/pyrethrin sprays or check the OMRI website for a list:

Aphids also love plants that are over-fertilized with nitrogen. If they are a constant problem despite other control efforts, you might be adding too much nitrogen to your potting mix or through fertilizer applications. A tissue test to determine nitrogen levels may be in order if you are having ongoing issues with aphids and other sucking pests.

As always, crop rotation and good sanitation practices can help control aphids in the long run.



  • Deep Winter Greenhouse
    University of Minnesota website with resources on greenhouse building, production, a chance to connect with others and more. Includes enterprise analysis from seven deep winter producers in MN.
  • Growing Under Cover
    Farmers and other growers seeking to extend the production season, increase yields, or mitigate weather conditions can turn to a new Kansas Rural Center publication for a thorough assessment of which “polytunnel” options may work best for their situation. Growing Under Cover provides practical information and resources to assist growers in Kansas, or similar climates, who are aiming to avoid common mistakes and tunnel disaster and to maximize return on investment from both high and low polytunnels. The publication is available free, online.
  • High Tunnels and Other Season Extension Techniques
    Learn about structure types and construction, cultivar selection, and management of fertility, pests, water, and temperature. Useful for experienced growers and those who are new to season extension. Sustainable Agriculture Research and Education (SARE)
  • High Tunnels Manual (2.5 MB PDF)
    A manual describing how to use low-cost technology to increase yields, improve quality and extend the season. Written by Ted Blomgren and Tracy Frisch.  Cornell University and Regional Farm and Food Project
  • Minnesota High Tunnel Production Manual For Commercial Growers
    Published in 2010 and updated in 2012.  University of Minnesota Extension
  • Season Extension: An Overview
    Don’t know a hoop house from a greenhouse? Learn the basics of season extension. Sustainable Agriculture Research & Education
  • Season Extension Techniques for Market Gardeners
    This publication describes season extension techniques and provides sources for equipment, supplies, and further information.  ATTRA
  • Season Extension Tools & Techniques (1 MB PDF)
    Information and tips on marketing and market outlook, specific tools and techniques, and economic considerations.  University of Kentucky
  • Sustainable Pest Management in Greenhouses and High Tunnels (1.37 MB)
    Growers using greenhouses in which temperature, light and relative humidity are controlled have relied for many years on releases of natural enemies to manage aphids, thrips and two-stopped spider mites. This fact sheet provides detailed advice on how growers can use natural enemies to manage insect pests in minimally heated greenhouses and unheated high tunnels. Sustainable Agriculture Research & Education
  • Thermal Banking Greenhouses
    Thermal banking is the storage of heat that accumulates during the daytime and can then be used to keep the greenhouse beds warm during cold periods.  Sustainable Agriculture Research & Education








From the Organic Broadcaster

Easy-to-grow microgreens can add year-round farm income
November  | December 2018

For the farmer, microgreens can be a valuable addition to farm enterprises, providing cash flow even in the winter months. Read more.



University partners with local farmers on greenhouses for winter production
January  |  February 2018

Through its Deep Winter Greenhouse initiative, the University of Minnesota Extension’s Regional Sustainable Development Partnerships (RSDP) and five producers throughout the state are testing prototypes to see if it is possible to profitably grow crops in Minnesota winters. Read more.



Innovative system uses composting process to heat high tunnel
July | August 2014

High tunnels allow vegetable farmers to extend the growing season, but often require supplemental heat to protect plants during spring and fall cold spikes. Read more.


What you need to know before buying/building irrigation system
May | June 2014

With the changing climate delivering hotter, drier summers, many farmers are seeking solutions by irrigating crops. Read more.



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