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:
- 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.
- 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 works well, as long as the plastic is not touching the plants.
- 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 cloth over any blooming or budded up shrubs. If possible, drape cloth to the ground and secure. Big Leaf Hydrangeas, Hydrangea maculata, 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.
- 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: Onions, cabbage, broccoli, cauliflower, carrots, turnips, kale.
Potatoes, asparagus and rhubarb will send up new growth from dormant eyes if the top growth was 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.
- 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 as plus as too many fruits reduces 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.
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 best planting times for your plants. A few tips:
- Historical first frost date in the St Louis Missouri area is October 15, last spring historical frost date April 15. Of course, Mother Nature likes to throw out a frost before or after these dates to keep us humble.
- 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.
- 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 danger of frost has passed. They include: tomatoes, peppers and other warm weather vegetables and annuals.
- Perennial 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 a clumpy, dense soil most plants hate. Perennials and shrubs can be planted anytime March through October. To give plants plenty of time to settle in before hard winter hits-around Christmas time-plant perennials and shrubs 6-8 weeks before December 25.