Beautiful gardens by William Johnson
WHEN DID our landscapes move north? Are we not situated on the balmy Gulf Coast of Texas? Should our USDA plant-hardiness-zone map rating be changed?
Temperatures dipped low enough and for long enough to exact a toll on cold-sensitive landscape plants in the county a few days ago.
What’s a gardener to do? It’s easier said than done but do not panic at the miserable appearance of cold-sensitive plants just after a hard freeze.
Several factors influence the extent of cold injury suffered by ornamentals and even certain types of fruit, especially citrus. Such factors include variety – some might be more cold-tolerant than others – and age; recent plantings that are not well established are more susceptible to freeze injury. A very important factor is the general health of a plant.
However, you can take steps now to help reduce the occurrence of additional injuries to ornamental and fruit plants resulting from the latest cold snap.
• Keep your plants well watered. Watering is an extremely important plant-saving practice for winter. It is very important that those in containers as well as in the soil be provided adequate moisture throughout the winter season.
The wind in the winter, like the sun in the summer, will dry soil so be especially sure that it is well watered if another cold snap appears to be coming to prevent plant roots from drying out.
• Even though woody plants might appear to be in poor condition, do not do any pruning until late winter or early spring. This applies to all citrus and ornamentals, including palm trees.
Heavy pruning now can stimulate new growth, which could easily be burned back if another cold snap occurs. Also, it is easier to prune and shape ornamentals after the full extent of any damage is known.
• Proper fertilization is a key to winter hardiness for many perennial landscape plants. Our local soils are usually low in nitrogen and potassium, the elements that plants use to boost their cold protection defense during winter.
Even if it’s been a while since you fertilized your perennial landscape plants, do not start fertilizing cold-stressed plants until they have resumed active growth in the spring. The use of fertilizer now might stimulate new growth that’s very susceptible to cold injury. Also, fertilizer salts could cause further injury to stressed root systems.
• Damage to most citrus fruit occurs when temperatures fall below 28°F for at least four hours. Grapefruits are the most cold-hardy of the citrus fruits, in part because of their thick skins, followed by oranges, mandarin types, lemons and limes.
Large and thick-skinned fruits are more cold tolerant than small, thin-skinned species. When fruit freezes, it can still be used for juice if quickly harvested.
• Do not be in a hurry to prune plants such as hibiscus, pentas, lantana and plumbago. They can be cleaned up a little if they look unsightly or if your friendly neighborhood association sends a letter, but don’t cut them all the way back unless you’re willing to give up a security layer for the plant. Leave some of the damaged material intact.
Try to be patient and, where feasible, don’t remove dead leaves and twigs of bananas, umbrella plants and suchlike until at least mid March. Should yet another cold snap occur, the dead foliage can help protect the rest of the plant from cold damage and can aid the plant in a quicker recovery.
• Plants with thick, fleshy roots, like cannas, firespike, four o’clocks and gingers, can be cut all the way to the ground and they will regrow next spring. Even after severe freezes, most plants like bougainvillea and hibiscus come back from the roots, so don’t give up on them.
• Most cool-season vegetables fared well during the cold snap, with broccoli, cabbage, cauliflower, collards, kale, mustard and onions coming through fine. The cold can make these cool-season vegetables taste even better.
However, unless they were protected, warm-season vegetables bit the dust and it’s time to remove them from the garden.
• Some plants, of course, won’t stand any freezing weather regardless of how many toughening techniques you employ. That’s one of the reasons for using only thoroughly hardy plants in the basic framework of your landscape – such as for shade trees and screening and foundation plantings. Use the less hardy, more tender plants – flowering annuals, bougainvillea, hibiscus, etc – as filler to add interest to entryways, flower beds or borders.
The full extent of injury to many plants might not become apparent until summer. It will be of utmost importance that cold-stressed plants are also provided good care throughout the coming growing season to safely achieve a full recovery.
William Johnson is a horticulturist with the Galveston County office of Texas A&M AgriLife Extension Service. Visit his website at aggie-horticulture.tamu.edu/galveston/index.htm.