This story was originally published in March 2019.
Some gardeners live in fear of frost. Even as the days begin to warm, a surprise cold snap could mean the end of the road for precious tomatoes and peppers sown too soon. Growers in a handful of tropical areas may not experience such trepidation, but for most gardeners, the fear of frost is alive and well.
There are cold hardy vegetables that can be planted in your garden before, though. In fact, there may be more of them than you think.
Certain cold-hardy plants can survive a light or moderate frost and prosper even if spring temperatures have not quite stabilized. These plants can thrive in cold soil temperatures, compared to their later season counterparts that need a warmer growing medium.
Carrots, corn, parsnips, spinach, turnips, peas, onions, lettuce and seed potatoes can all be sown directly into the ground once the soil has thawed enough to be workable.
“Plants like carrots and even corn, they are really hard to transplant and they will germinate right into the soil anyway,” said Wendy Wilber, statewide Florida master gardener coordinator at the University of Florida.
Some long-season seedlings can also be planted before the last frost. Broccoli, beets, cabbage, cauliflower and kale can all be started from seed indoors before bringing them out several weeks before your projected frost-free date. Seedlings should be “hardened off,” or brought outside to face the elements during the day for about a week before you transplant them in order to let the plants acclimate to the elements.
“You’re gradually exposing them to lower temperatures, increased air flow and increased light,” said Kate Garland, horticultural specialist at the University of Maine Cooperative Extension. “Even a week is helpful.”
If you do not start your plants from seed, you can still purchase seedlings from a nursery to plant before the last frost. Just make sure those plants have been properly hardened off as well.
“Ask the nursery staff,” Garland advised. “You can also tell by looking at where they’re stashed. If they’re outside, then they’re probably hardened off, but it’s always good to double check.”
Some perennial crops can be planted before the last frost-free date as well. “Things like asparagus and rhubarb and strawberries, and woody plants like blueberries, raspberries and fruit trees do better if they’re planted a little bit early,” Garland said.
Finding your last frost-free date
To avoid planting too early, be sure to check the frost-free date for your area. You can call your local cooperative extension for the information, but there are a number of online search tools that will provide the projected last frost date based on your ZIP code.
The National Gardening Association provides a range of dates and the probability of freezing or below freezing temperatures for each based on data from the National Oceanic and Atmospheric Administration. Dave’s Garden’s search tool does the same with data from the National Climatic Data Center.
Precision can be important when avoiding frost, especially for cold, northern climates. Garland recommends exercising caution.
“I usually set the threshold of 10 percent of having less than 32 degrees,” Garland said. “I’ve gotten my heart broken before.”
Garland said to look at the current weather patterns and projected forecast about a week before you plant as well.
“Curveballs late in the season are common,” Garland said. “It’s really important to look at that 10 day forecast before you plant.”
The growing season starts earlier and the risk of a surprise frost late in the season is lower in warmer states, but it is still important to be vigilant.
“We plant quite a lot in January and February, but we don’t plant our spring crops much before [the last frost-free date],” Wilber said. “We’ve had a couple springs where the climate has been very warm up until that last frost date, and then we still get a surprise freeze. One year, we got a freeze on St. Patrick’s Day.”
There are season extenders that can help protect your crops in case of any unexpected cold snaps.
“You may get caught by a light freeze. Be ready, because mother nature is mean and she likes to laugh at us,” Wilber said. “Have your season extenders in place whatever your favorite one is.” Wilber said her personal favorite is a frost cloth to cover plants in case of a cold weather emergency.
Planning your planting before the last frost-free date
When exactly you will plant or transplant your crops before the last frost will depend on where and what you plant. For example, broccoli can usually be planted two weeks before the last frost date, while cabbage and collards can go out about four weeks before.
To ensure proper timing, you can use a handy planting calculator like this one from Johnny’s Selected Seeds, or contact your local cooperative extension for more resources.
If you are looking to maximize your yield, Wilber said it is best to have a plan. Keeping track of where you grow which crops also helps you prevent growing the same things in the same spots season after season, which can cause fungal pathogens and insects to build up.
“I recommend folks rotate their crops so they can have a plot plan,” Wilber said. “You can have it in a beautiful garden journal.”
Even though there are lots of options for planting before the last frost-free date, Garland said not to feel pressured to start too early.
“You can plant late and still get a great yield from your garden,” Garland said. “Don’t feel rushed.”