Even though the temperature reached 80 degrees this past Monday, I think it’s important we talk about FREEZE PROTECTION of landscape plants. I KNOW -- TRY NOT TO LAUGH!!! Frankly, I was surprised how few people covered their susceptible plants this past week when we temperatures dipped into the high 20s two nights in a row. Nevertheless, it was the bone-headed, plastic users that I did see that has prompted me to get this message out ASAP.
I personally got out and covered all my tropical landscape plants that are freeze susceptible, but I exclusively use the freeze protection fabrics/frost covers, and would never, ever recommend the use of plastic trash bags for freeze protection.
Typically, I also see many people throw the laundry at freeze protection. Sheets, blankets, flannel shirts and old pajamas – people will try anything they have, rather than invest in proper frost cover/freeze blankets. And while clothes and sheets do work better than plastic, there’s not near the level of protection that you can get with the frost cover/freeze blankets.
That’s because the patented freeze protection fabrics are spun/manufactured in such a way that they can create a difference in temperatures as much as 6-8 degrees warmer underneath that blanket. Whereas, a single bed sheet may only create a 2 degree difference. Thus, if the temps are 27-28-29 degrees the temperature under the frost cover is above freezing, while the blanket or sheet can still be below freezing.
Speaking of temperatures, I’ve said it before on The GardenLine for years and I stick by it, that 25 degrees is kind of a magic number for us in the Houston area when it comes to more-than-normal freeze protection. In other words, 32, 31, 30 degrees for very few hours doesn’t do much to prompt me into frantic freeze protection. I think that’s because most of the tropicals that are available to us these days can actually take a few hours of freezing or just below. And if you look at cold-hardiness charts and descriptors of plants “anything below 25” seems to be a common thread in the need to protect.
Let me give you a great example: Over fifteen years ago Queen Palms were not planted as much as they are now, because they were considered very susceptible to freezing temperatures. I haven’t covered a trunk of any of my Queen Palms in years, and we’ve gotten temperatures as far down as 26 for several hours on many of these Queen Palms in the last dozen years. They are adapting to cooler temperatures for sure, but they are simply breeding more cold-hardy Queen Palms as well. I think it was over 10 years ago the last time I heard of any Queen Palm lost in a freeze.
It’s also laughable to see people needlessly cover typically hardy plants like Azaleas. The fact is most azaleas require cold weather to help the plant set up its blooms for February through March. The only time I would ever cover Azaleas is if they were covered in blooms and we were on the verge of an ice storm.
So, what do you cover for the most part? Herbaceous or green-stemmed tropicals as well as tropical vines are the best examples of what needs to be covered. Examples: Hibisicus, Gingers, Cannas, Mandavilla, Bougainvillea. You can even find garden books written for Texas that claim that cold-sensitive palms such as Sagos and Dwarf Pygmy Date Palms need protection. I use that magic number of 25 degrees or below as my guidepost for covering those. I’m confident that light freezes for a few hours are harmless to those palms and of course harmless to all woody-stem, woody-branch plants. If the landscape shrub is normally considered an “evergreen” it can take temperatures well into the low twenties without ever showing any signs of damage. For the typical tree, shrub, woody vine to be freeze damaged in Houston and the Gulf Coast, we would have to experience temperatures as low as the teens and single digits for several days in a row.
And outside of the freeze blankets/frost cover protectors (unless you want to use sheets and blankets) here are the other basic tenets for freeze protection of landscape plants.
Mulch, Mulch, Mulch! Mulching all landscape plants is a great cold-protection technique. Granted, while our temperatures are never cold enough to freeze the ground, slightly exposed roots are susceptible to winter damage. Plus, the mulch also traps the warmth that’s in the soils and it helps preserve moisture that is also a great defense for freeze protection.
Water, Water, Water! Water the entire landscape as well as containers. This may sound counterintuitive to some, but well-watered plants are less likely to suffer freeze damage. Dry soil is a poor insulator for the roots, while moisture in the soil can also be drawn through the plant to reduce desiccation (drying out) of leaves in cold winds. Again, our soil doesn’t freeze, so watering the soil is a great idea to aid and abet in freeze protection. Cover, Cover, Cover! I say invest in frost covers/freeze blankets. The neat thing about freeze covers is that you can leave them on the plants you’re protecting for days. This is important to those of us “lazy” gardeners who so want to be participating in the horticultural aerobics of “cover; uncover” each and every day. They are designed in such a way that they can still allow for light and air circulation. Unlike blankets and sheets (as especially plastic) which would need to be removed the next day the temperature immediately gets above freezing. You can also improvise “covering” plants with big boxes. Just make sure they too are removed the next morning the minute the temperatures get above freezing.
Lights, Lights, Lights! Use the Christmas lights, hopefully before you put them all up for the season. There is heat generated from those lights and then with a cover of some kind, that heat is mildly trapped. I’ve seen lights used for Sago Palms and vegetable crops for the most part in January and February) Uncover, Uncover, Uncover! It’s already been alluded to, but when the temps get above freezing (33 and above), unless you’re using frost blankets/freeze protector fabrics, remove everything else the next morning to let the plant processes resume normal functions. No Plastic, No Plastic, No Plastic! It’s as simple as this: Plastic that is touching leaves will be a conduit for freeze damage. The plastic still absorbs freezing temps and if a hibiscus leaf or stem is in contact with said plastic its drawing that cold to and through the plant. Yes, plastic strapped around a make-shift structure or box (often called a cold-frame) can act like a greenhouse, but it’s the people who simply take a plastic bag and covers a plant with it are the ones that are doing more damage than good.
Wind Chill is not normally a factor on plants, as opposed to human skin. If the temps are in the mid 30s, but the wind chill is say 27, I don’t feel you need to cover your plants if you’ve done everything else in the watering and mulching departments.
Finally, what if you have freeze damage from that January 2nd & 3rd freeze? For the most part just leave it alone. On anything that has woody stems/woody branches, you have to resist the temptation to get out and prune back the freeze damage. Let the dead leaves and stems near the tops of the plant provide additional protection for the remainder of the winter. The best time to prune back any of these plants is after they begin a small sprouting period early in the spring. That way it is obvious to determine exactly where and what you need to prune.
Hibiscus are the best examples of the need to be left alone. Yes, there are some exceptions in the “tropical” landscape plant world that can and probably should be pruned a bit during winter damage. The best example would be banana trees. First, remember that the fronds/leaves are expendable at anytime. They will go brown at the first cold spell and should be removed the minute they look bad. But the trunk is the important part, and should be protected from winter freeze damage when possible. People have used everything burlap to newspapers to carpet remnants for trunk protection. However, if the top of the trunk is freeze damaged you will need to cut that part off. It usually manifests itself in a mushy mess, and if left to its own devices that mush will continue to move on down the trunk. So, always be prepared to cut back “fleshy”, non-woody plants when they have suffered such freeze damage.
While I’ve focused on Landscape Plants, all of this applies to vegetable gardens being grown in winter too, with the exception of tomatoes. Everybody has their own method and I would love to hear your ideas. In the meantime, outside of home made cold-frames, I think the coolest way to protect susceptible veggies is with a little something called a Water Wall.
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