Rest easy Gardeners,

In St Louis we always experience late spring frosts and early fall frosts. Over the years we have learned the best way to protect our darling plants from these cold snaps. A few of our tried and true techniques:

1. If not planted in the ground, move sensitive plants into an area above freezing…your home, garage, or storage shed. Important note: most tropical plants and houseplants, and most annual plants do not like cold nights, they are best moved into your home.
2. If planted in the ground, water the soil well – wet soil holds the heat better than dry soil. Cover plants with cloth; bed sheets and towels work great. If possible, drape the cloth all the way to the ground and secure. Newspaper and straw can also be used. Do not use plastic. Wherever the plastic touches the plant will burn. However, plastic pots placed over the plants work well as long as the plastic is not touching the plants.
3. When the temperature gets above freezing you can safely remove any coverings.

Cover Or Not To Cover?

Trees: Do not need to be covered and tolerate frost.

Shrubs: Most shrubs tolerate frost, although flowers may be lost. Many tight flower buds that have not opened tolerate frost. Place a cloth over any blooming or budded-up shrubs. If possible, drape the cloth to the ground and secure it. Big Leaf Hydrangeas, Hydrangea macrophylla, do not tolerate frosts well and should be covered to prevent leaf damage and flower loss.

Perennial Flowers: Most perennial plants do not suffer frost damage and do not need to be covered. Frost sensitive perennials include Hostas and Bleeding Hearts. They should be covered to protect their foliage and flowers. Cover any blooming or budded up perennials.

Vegetables:

• Plants to move inside: Tomatoes, peppers, eggplant, and others that will not survive frost.
• Plants to cover: Potatoes, radishes, spinach, leaf lettuce, beets, mustard.
• Plants that do not need to be covered are onions, cabbage, broccoli, cauliflower, carrots, turnips, and kale.

Vegetable Notes:

Potatoes, asparagus, and rhubarb will send up new growth from dormant eyes if the top growth is killed.

Fruit Trees and Other Fruits and Berries: Plants will be fine, but frost will kill buds. As a rule, a temperature of 28 degrees will kill 10% of the fruit buds but a temperature of 25 degrees will kill 90%.

• Cover if they are in bloom: Strawberries.

Fruit Notes:

• Peaches and apricots: Their buds can be killed by the extreme cold.
• Apples and pears: Frost can thin the crop but not eliminate it. Sometimes this is a plus, as too many fruits reduce quality. Ideally, you’ll want an apple or pear every 4-6 inches.
• Plums: Fruit will not set if temperatures reach 25 degrees or below.
• Thornless Blackberries: Sever cold snaps will kill fruiting canes to the ground but new canes will emerge.
• Raspberries and thorny blackberries: Can tolerate frost with minimal damage.

Planning Ahead

You can pretty much count on getting unexpected frosts in the St Louis area. Yet, with a little planning, you can be ready. Historical first frost and last frost dates will aid you in selecting the best planting times for your plants. A few tips:

1. The historical first frost date in the St. Louis, Missouri area is October 15, and the last spring historical frost date is April 15. Of course, Mother Nature likes to throw out a frost before or after these dates to keep us humble.
2. Our environment is loaded with “microclimates.” You may have a place in your landscape that stays a little warmer or colder. These areas can aid you in growing better plants. Buildings or larger trees and shrubs can protect plants from unexpected frosts. Observe temperatures in these areas.
3. Some plants tolerate frost well and can be planted in early spring or even late fall. They include pansies, lettuce, spinach, kale, and other cold-weather vegetables, trees, shrubs, and perennials. Many others should be planted when the danger of frost has passed. They include tomatoes, peppers and other warm-weather vegetables and annuals.
4. Perennials and shrubs can be planted anytime in spring when the soil has dried out a bit and can be worked. Working too wet soil causes clumpy, dense soil that most plants hate. Perennials and shrubs can be planted anytime from March through October. To give plants plenty of time to settle in before hard winter hits around the December holiday time, plant perennials and shrubs 6-8 weeks before December 25.