This month I am covering several topics of interest based on phone calls and information received from horticulture specialist with the LSU AgCenter. The fact that mother nature has sent us an early reminder of winter has prompted many calls on topics of plant protection in the landscape. Lack of preparation or plans causes one of the biggest issues that I see that sends many gardeners into a panic when freezing temperatures are predicted. Every gardener should have protection plans in place when herbaceous tropical or woody tropical plants grow in the landscape when those plant that are not able to survive predicted low temperatures.
You may recall earlier information regarding plants and degree of cold hardiness or cold tenderness, the length of time that plants are exposed to freezing temperatures usually determines the extent of injury. Plants exposed to temperatures in the mid – 20’s, for 4 hours, will sustain less damage than if exposed to the same temperatures for 8 hours. Whenever plants are covered with some type of fabric while it is raining, if it freezes the weight of the fabric can damage plants; support in the form of three simple, wooden stakes will help. If using plastic to cover plants, it will shed water and weight is not a problem; however, removing the plastic or venting the plastic on sunny days is important to prevent injury to plants from heat buildup. Additionally when covering plants, drape the cover over the entire plant until it touches the ground, then anchor the covers with pins , bricks or other heavy objects. This will be more effective than covering the plant and tying off the cover before it touches the ground. It is felt that, especially when there is bare soil beneath the plant, heat is absorbed during the day and released at night.
For this reason, it is recommended that the ground beneath citrus trees be left bare during the winter months instead of being mulched. Bare soil absorbs heat and releases it later, and the heat release can make a difference in the degree of damage during periods of freezing temperatures. With citrus trees, remember it’s important to protect the graft union located on the lower trunk. This graft union can usually be identified by a slight swelling just below the regular trunk and a few inches above the soil line. The graft union can be wrapped with old cloth material, foam, mulched with leaves, pine straw or any material that can serve as insulation. Even if the top of the tree killed as long as any part of the trunk above the graft union survives, sprouts will be capable of producing quality fruit. If, however, the graft union or areas above the graft union doesn’t survive, sprouts that are produced below the graft union near the soil line usually will be wild rootstock which will not produce quality fruit. Although cold , dry winds can dry out leaf tissues and cause brown edges, plants don’t feel wind-chill. When low temperatures are predicted, focus on the actual temperatures rather than wind-chill. When weather forecasts predict that the actual temperature is getting down to 38 degrees with a wind-chill of 25, you don’t have to be concerned about a freeze.
Prune off any freeze damage or injury to gingers, cannas, philodendrons, or other herbaceous tropical. Placing between four and six inches of mulch such as pine straw around the base of plants will help protect roots and rhizomes. Move tender container plants indoors on nights when temperatures are predicted to be in the low 30’s or lower to prevent damage. Leave them inside in a sunny window or place them back outside when the freeze is over.
Many garden chemicals are water based and can be destroyed by freezing. Those loss of chemicals can be expensive and spilled pesticides can create dangerous conditions. Keep chemicals in locations that don’t freeze, and if there are children in the house those chemicals should be stored safely (preferably in a locked location).
Fall tomatoes ripen poorly in when temperatures are cool outside. Don’t wait for them to turn red before you pick them. As soon as fruit start to turn whitish or pink, harvest them and place them inside at room temperature until they turn red. Light is not necessary for ripening. Harvest any green fruit of reasonable size if a freeze is predicted, and use them in your favorite green tomato recipes. For citrus trees, any time freezing temperatures are predicted below the upper 20’s, all fruit should be harvested.
November through March is a good time to plant pecan trees. The more resistant varieties such as Sumner, Candy, and Elliot are recommended. Elliot is the top choice for disease resistance for home gardeners! When we refer to disease resistance in pecan varieties, we are primarily referring to Pecan Scab: a fungus disease that severely impacts the quality of nuts. Also, remember that resistance doesn’t mean immunity!! Harvest broccoli when the largest buds in the head are the size of the head of a kitchen match. Don’t focus on the overall size of broccoli head itself, as that is not an indication of when the broccoli is ready for harvest. If you begin to see yellow flowers you’ve waited too long. If temperatures in the mid 20’s are predicted harvest mature heads of broccoli; even though the plants are hardy, the heads are susceptible to freeze when the temperatures fall to 25 degrees or below.
Varieties of certain shrubs such as azaleas, nandinas or junipers may develop a burgundy tint to their foliage during cold weather. This is normal and no cause for concern. They will turn green in the spring.
Bed preparation is the key to long-term landscape success. Raised beds are almost essential in our area for successful landscape plant establishment because of our soil type and our poor internal drainage. A raised bed at least 6-8 inches deep can be enclosed with decorative bricks , concrete edging, landscape timber, or railroad ties. Chemically treated wood is safe to use around ornamental plants. A raised bed doesn’t necessarily have to have a physical border or edge. If properly prepared and mulched when completed, the soil should hold in the bed and not wash away even in heavy rainfall.
One method of bed preparation that is used at the Hammond Research Station whenever annual bedding plants, herbaceous perennials, or small shrubs are planted is the “kill, dump, rake, and plant method.” Kill the area you wish to plant with glyphosate herbicide, repeat in 10 to 14 days to kill any lasting vegetation. Obtain good landscape bed builder soil from a reputable dealer, dump this soil over the area where vegetation was killed. Then rake and smooth bed to an average depth minimum of 6 inches. Ideally wait for a rainfall to settle the soil prior to planting. It seems to be easier to lay the mulch down on the bed, then plant into it instead of mulching after planting.
HAPPY GARDENING !!!!