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Mr. Smarty Plants - Freeze damage on perennials in Austin

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Thursday - December 10, 2009

From: Austin, TX
Region: Southwest
Topic: Pruning
Title: Freeze damage on perennials in Austin
Answered by: Barbara Medford

QUESTION:

Dear Mr. Smarty Plants, The recent hard freeze in Austin really took a toll on the plants I put in the ground in early October. The leaves of my salvia, lantana and esperanza are completely black! Is there anything I can do or are they gone for good?

ANSWER:

 

We have three questions on the docket regarding what to do after the sudden hard freeze that occurred recently in Central Texas; in fact, we are still dipping below freezing at night frequently. With your permission, we will address all three first as a group, and then, for each question, the individual plants involved. One thing that applies in every case is, don't fertilize. Plants should be fertilized in the Spring, when you want to encourage new shoots to appear. The last thing you want to do is encourage new shoots now that will put more stress on already-stressed roots and probably just get frozen back again.

You may already know what happened; actively growing plants still have water in their upper structure, particularly the leaves. A sudden hard freeze causes that water to expand, bursting cell walls in the leaves, and they quickly turn dark and look pathetic. What made this freeze worse was that it was earlier than we ordinarily expect these conditions in this part of Texas, very sudden, temperatures went down very far, and remained below freezing for several hours. A gradual decrease in temperature over a period of time increases the ability of plants or plant parts to withstand cold temperatures. A sudden decrease in temperature in late fall or early winter usually results in more damage than the same low temperature in January of February.

Your first plant is salvia; there are 37 salvias in our Native Plant Database, and 18 native to Texas. We picked one that we know grows in the Austin area to use as an example: Salvia azurea (azure blue sage). Since we have always recommended cutting salvias back to about 6 in. after the first freeze, this would seem to be the time to do it. The reason we like to leave 6 inches of stalk above the ground is so you know where it is, and don't accidentally pull out the new sprouts in the Spring, believing they are weeds. It seems unlikely that this plant will suffer permanent damage.

 

There are a number of lantana cultivars and non-natives in the commercial trade now, many of them considered sub-tropicals, and since the Lady Bird Johnson Wildflower Center is dedicated to the use, care and propagation of plants native not only to North America but to the place where they are being grown, we can't vouch for the hardiness of any but the Lantana urticoides (West Indian shrubverbena), native to Texas. First, use the thumbnail test on the branches of the plant you have. Scratch off a very thin layer of the outer bark. If the area under it is still green, the branch is alive, even if the leaves are dead. If it is black or slimy under that first layer, the plant may have sustained more severe damage. We would recommend that you prune it back pretty hard, mulch the root area to protect against future bad surprises, and play the waiting game. 

Tecoma stans (yellow trumpetbush) -
"Conditions Comments: Yellow bells produces great, yellow, attention-grabbing blossoms. The plant will not tolerate extreme cold well, but cutting it back to the ground in winter can help maintain yellow bells in your spring and summer landscape." In the interest of not having to look at the mess, go ahead and prune it down. This plant occurs naturally more in the southern and extreme western parts of Texas, and is considered marginal this far north. However, we believe that the "marginal" refers to the fact that it can be evergreen, and obviously is not evergreen here. With a little tender loving care, mulch on the roots, it will probably be fine. 

From our Native Plant Image Gallery:


Salvia azurea

Lantana urticoides

Tecoma stans

 

 

 

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