Tender & Hardy Plants

There are many ways that we classify plants but one of the most important for gardening or landscape purposes is how they respond to cool and cold temperatures. This applies to flowering plants and vegetables. In its simplest form plants are considered hardy, semi-hardy or tender. Some of these plants do well direct-seeded into the garden while others do better as transplants.

Hardy

Hardy plants are those that will tolerate frost or freezing temperatures – down to 25 degrees Fahrenheit and even colder for some, such as kale. As the days get longer and soil temperatures begin to warm, these plants have built-in antifreeze that keeps them from getting damaged on nights. As long as daytime air temperatures reach above about 40 degrees Fahrenheit, many will grow and thrive. Generally, hardy plants taste best and do best in cooler temperatures, not during the hot summer months. With proper care and protection, some will even grow during the winter months. Examples of hardy vegetable plants include:

  • cabbage
  • garlic
  • kale
  • leeks
  • mustard greens
  • onions
  • parsley
  • peas
  • radishes
  • spinach
  • turnips

Semi-hardy

Semi-hardy plants will tolerate light frosts down to 29 degrees Fahrenheit. As the days get longer and the soil warms, even more, these plants will grow well and light frosts are not a cause for concern. Semi-hardy vegetable plants include:

  • beets
  • carrots
  • cauliflower
  • celery
  • corn {young corn plants will tolerate light frost but are more susceptible to frost damage as the plant becomes larger}
  • lettuce
  • potatoes
  • Swiss chard

Tender

Tender plants are those that will not survive even the lightest frost. As a matter of fact, some will suffer chilling damage from temperatures as low as 35-40 degrees Fahrenheit. Tender plants need to be protected if there is a risk of frost. If protection is not available, they should not be placed outside until after the last chance of frost is past. Most experienced gardeners in our area will not plant tender vegetables out without protection until after Memorial Day. Tender vegetable plants include:

  • beans
  • cucumbers
  • eggplant
  • gourds
  • melons
  • okra
  • peppers
  • pumpkins
  • squash
  • sweet potatoes
  • tomatoes

Hardening Off

Regardless of the hardiness of your vegetable plants, if they have just been purchased from the greenhouse or nursery center you need to be sure they are hardened off before they are planted in the garden. Any sudden change in environment can throw the plant into shock or even kill it. The environment in our yards and gardens is usually drier, windier and has brighter sunlight than where they have been growing. If the garden center has them outside all the time and they look healthy then they are probably hardened off adequately.

If your new plants come right from a controlled environment then it is best to take about one week to adjust to your yard or garden. Make sure they are adequately watered. For the first couple of days place them outside during the day in a protected, semi-sunny spot, especially out of the wind and bring them into a shed or garage at night. The next couple of days gives them increasing amounts of sunlight in a less-sheltered location during the day and in a sheltered location at night. Continue to increase the amount of light and exposure to winds. Keep in mind that the spring winds are probably the worst enemy of your new plants, so protecting them from the wind even after they are planted will help them be more successful.

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