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Garden Season Extenders –
Start Earlier and Grow Later

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Nothing can kill your gardening fun like the end of the season. Days get shorter, and so do smiles. Yet there are ways to stretch your outdoor gardening for several additional weeks to maximize your fun. While they extend the gardening season, they also have the following benefits in common:

  • They capture daytime heat generated by sunlight and retain it overnight, providing additional warmth to plants.

  • They recycle energy and do not require batteries or electrical wiring.

  • They are useful in late winter/early spring to get the year’s garden going earlier and to harden off plants that have been started indoors.

  • In the fall, they can buy gardeners 3-6 weeks of additional growing time as the weather cools.

  • They are low tech, yet still effective.

Here is a sampling of common season extenders used by gardeners across the country.


Floating Row Covers

Made from spun polyester or polypropylene fabric, these sheets of almost weightless material are laid right on top of garden beds. Their loose weave transmits light, allows some airflow, protects against hard rains and keeps out larger insects. Plastic pegs hold the fabric edges snuggly against the garden soil.  Row covers can stay in place for weeks and do not need to be adjusted daily to avoid having plants overheat. The temperature retention is typically 4 to 6 degrees and row covers provide frost protection to about 28 degrees.


Grow Tunnels

A frame constructed from bent metal rebar rods pushed into the soil or a curved tunnel of hardware cloth serves nicely to support wide strips of 4-mil clear plastic film. In addition to retaining sun-generated heat into the night, this approach provides small plants some protection from chilly winds. Be sure to plan for sunny day ventilation as interior temperatures in closed tunnels can rise quickly and “cook” plants. Grow tunnels typically add an additional 4 to 8 degrees of night warmth and protect from frost damage to about 27 degrees. Check out this article for 13 different kinds of grow tunnels and a tutorial on how to build each one. 


Cold Frames

Cold frames are boxes built to block the wind and create warm pockets for small numbers of plants. Designs for these frames may be fancy or simple, for single or multi season use. The frame sides are typically made from wood, concrete blocks, bricks, or bales of straw, with covers often fashioned from recycled window sashes. Hinged tops allow the heat that builds up on sunny days to be managed and at night these are closed to retain the day’s warmth. Cold frames offer 5 to 25 degrees of additional thermal protection, depending on the materials used and orientation to the sun. This blog offers 26 different tutorials. 


Space Blankets

Campers who backpack and sports fans who cheer from stadium seats in cool autumn weather are familiar with space blankets. Made from a thin sheet of aluminum backed with 4-mil plastic, these can be draped over a plastic tunnel (see above) with the shiny side facing the plants and the edges flush with the soil. The aluminum reflects 95% of the heat back towards the plants and can add up to 20 degrees of nighttime protection. Space blankets must be removed during the daytime to allow sunlight to reach the plants. Good for small garden plots, these season extenders can be found at camping supply stores.


Wall ‘O Water

Designed to protect individual plants, these are open-top tents of adjoining flexible plastic water tubes. Gardeners plant in a sunny outdoor site, tuck a unit around a plant and fill the water tubes. During the day, the water heats up and at night the heat is released to warm the air around the plant. Wall ‘O Water units last several growing seasons and provide about 4-6 degrees of thermal protection. If this sounds too good to be true, this video shows exactly what a Wall O’ Water is and explains how it works.


As you can see, there are lots of options for extending your growing season.  Just a few more weeks in the spring or the fall means a few more weeks of joy. 

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