Guide to Hardening-off

 In order to give plants a chance to grow from seed to mature, fruit-bearing plant, gardeners need to start plants indoors during the cold late winter, and transplant them outside once the temperatures are warm enough to support proper plant growth.  “Hardening off” is the process of moving plants outdoors for a portion of the day to gradually introduce them to the direct sunlight, dry air, and cold nights.  Below are step-by-step instructions given by Norma Rossel, Quality Assurance Manager for Johnny's Selected Seeds.

  1. Harden off gradually, so that seedlings become accustomed to strong sunlight, cool nights and less-frequent watering over a 7-10 day period.
  2. On a mild day, start with 2-3 hours of sun in a sheltered location.
  3. Protect seedlings from strong sun, wind, hard rain and cool temperatures.
  4. Increase exposure to sunlight a few additional hours at a time and gradually reduce frequency of watering, but do not allow seedlings to wilt. Avoid fertilizing.
  5. Keep an eye on the weather and listen to the low temperature prediction. If temperatures below the crop's minimum are forecast, bring the plants indoors or close the cold frame and cover it with a blanket or other insulation.
  6. Know the relative hardiness of various crops. Onions and brassicas are hardy and can take temperatures in the 40's. After they are well hardened off, light frosts won't hurt them. Warm-season crops such as eggplants, melons and cucumbers prefer warm nights, at least 60° F. They can't stand below-freezing temperatures, even after hardening off.
  7. Gradually increase exposure to cold.
  8. After transplanting to the garden, use a weak fertilizer solution to get transplants growing again and to help avoid transplant shock.  Be sure to water plants after hardening them off.

Hardy plants, can be hardened off when the outside temperature is consistently above 40° F.  Half-Hardy plants may be hardened off at 45° F.


Recommended Minimum Temperatures
Hardy 40° F. Broccoli, Brussels sprouts, kohlrabi, cabbage, onions, leeks, parsley
Half-Hardy 45° F. Celery, Chinese cabbage, lettuce, endive
Tender 50° F. Squash, pumpkin, sweet corn
60° F. Cucumber, muskmelon
65° F. Basil, tomatoes, peppers


the terms "hardy" and "tender" relate to whether a crop can withstand frost. Hardy plants can, tender crops can't and half-hardy ones may be able to take brief, light frosts.  For more info, visit:

About Growing Gardens

Our Mission: To enrich the lives of our community through sustainable urban agriculture.
Our Vision: People experiencing a direct and deep connection with plants, the land and each other.
Growing Gardens is a 501c(3) non-profit organization dedicated to serving the Boulder County community through several urban agricultural projects:

  • The Cultiva Youth Project (ages 11 – 19) is a youth-operated market garden. Participants plant a two-acre garden and sell the produce at a local CSA (community shared agriculture) and share the proceeds with those in need in the community
  • The Children’s Peace Garden (ages 4 – 10) is a small garden designed to educate and facilitate younger children in gardening practices. Activities include field trips, harvesting, food preparation, beekeeping, and a summer camp.
  • Horticultural Therapy (seniors and people with disabilities) program facilitates social and intergenerational gardening activities, which help to increase motor, cognitive and psychological functions, and increases nutrition of participants through daily access to fresh organic produce, sunshine, and fresh air.
  • The Community Gardens (general public) offer those with no home-gardening space a place to garden for a small yearly fee.  Growing Gardens manages 11 community gardens in Boulder County.
  • Community classes are offered to the general public on a wide range of gardening topics.
  • Beekeeping classes (general public) are available to introduce the skill of beekeeping to participants.  Classes take place once per month.
  • Volunteer hours (general public) are held weekly on Tuesdays from 9am-noon, and Wednesdays from 1-5.  Just drop in, and immediately start working with Growing Gardens staff producing local, healthy organic produce!

To learn more about Growing Gardens and our programs, please visit

What is Urban Agriculture?

Urban agriculture is the practice of cultivating and caretaking of the land, processing and distributing food in, or around, a village, town or city. Urban agriculture in addition can also involve animal husbandry, aquaculture, agro-forestry and horticulture. These activities also occur in peri-urban (between suburbs and countryside) areas as well.
Urban farming is generally practiced for income-earning or food-producing activities, but also for recreation and relaxation. Urban agriculture contributes to food security and food safety in two ways: first, it increases the amount of food available to people living in cities, and, second, it allows fresh vegetables and fruits and meat products to be made available to urban consumers. Because urban agriculture promotes energy-saving local food production, caretaking of the land, urban and peri-urban agriculture are generally seen as sustainable agriculture. Urban agriculture has been gaining popularity in part due to the recognition of environmental degradation within cities through the relocation of resources to serve urban populations.