By Marc Hess
Editor, “Gardening South Texas,” newsletter
It is going to happen again. And we’re going to be surprised. Again. The first surprise was the ice apocalypse called Uri that caught us off guard between February 13th and 17th in 2021. A year later we were surprised again by a deep freeze that lasted from February 22nd through the 26th in 2022. Then in 2023, it snuck up on us in late January and stayed around until February 2nd of 2023. So what do you think just might happen this February?
The best chance that your garden and landscape have to make it through our next winter surprise is to prepare for it ahead of time. A hard freeze is considered 28°F or lower for two hours or more, killing crops and patio plants. In the big freezes the last three years, temperatures were at 0°F for several days.
Protect Your Irrigation System
During deep freezes ice will form inside any exposed pipes and equipment, causing them to burst. You will need to pay attention to your outside faucet covers and your landscape irrigation before you tend to your plants.
This is especially important because:
(1) water run-off from your outside watering system can freeze on sidewalks and roadways creating black ice and dangerous driving and walking conditions and
(2) freezing water can cause permanent damage to your equipment.
You will need to:
—-Be sure to turn off your irrigation at the irrigation controller, which is typically located in the garage. You can leave your irrigation system off until March or April and just water manually if needed.
—-Disconnect, drain and store anything connected to an outdoor hose bib. Your irrigation backflow device is expensive—and usually full of water—so it should definitely be protected from freezing temperatures if it’s installed above ground.
—- Pay attention to all your vulnerable pipes and hose bibs. They can be protected with fiberglass pipe sleeves, foam and faucet covers.
Not All Plants Need Protection from a Hard Freeze
If you plant native plants and other hardy plants, they’ll handle freezing temps well. These hardy plants may take some freeze damage but their roots rarely die and they will grow back when warm weather arrives. Covering only comes into play with tender annuals and semi-hardy plants.
Plants grown in pots and containers are particularly susceptible to death-by-freezing because their roots are directly exposed to extreme temperatures. Move your smaller pots and baskets inside. You may not be able to do that with your large containers. Try to roll them out of the north wind and under an overhead cover. Group them together so they keep each other warm. You may want to wrap blankets around the outside of the pots to keep the plants’ roots warm. When it warms up after a deep freeze move your container plants away from each over so that their leaves do not touch and spread their black freeze rot from one plant to the next.
Pond plants can be vulnerable too. When a hard freeze is predicted, just drop your floating plants like dwarf papyrus and the burgundy crinum to the bottom of the pond and leave them there until it warms up. Your pond will ice over but they will usually survive. Don’t worry about your hardy water lilies. They usually die back partly or all the way, but they will be back in the spring.
Freeze Hardy Perennials
Most perennial plants do not suffer enough frost damage to kill them and, therefore, they do not need to be covered. Freeze hardy perennials such as primrose, peonies, violas and heuchera can all be expected to survive the winter along with your irises and lily of the valley. Pansies are especially resilient to hard freezes but remember that they are short lived-perennials which means they will survive a winter or two but regardless of the weather, they will decline after that.
However frost sensitive perennials can be killed off in a period of prolonged sub-zero temperatures. The perennial that will need to be covered during harsh freezes include hostas and Bleeding Hearts (Dicentra). They should be covered to protect their foliage and flowers. Also you may want to cover up any blooming or budded up perennials. Often cyclamen works as a perennial in South Texas, and phlox also tolerates frost but they should be covered in the event of a deep freeze.
In general, tender plants like cannas will need to be cut back after freeze damage. The best practice is to plant them with this in mind, in combination with evergreen shrubs or other features that can conceal freeze damage.
Say Goodbye to Your Tender Annuals
Well, they are called annuals because you can expect them to die every winter under normal conditions. If you have any annuals then you had better protect them. Your beautiful, flowering, summer annuals are likely to die when temperatures dip to 32°F and lower. We love these annuals because they thrive in our long hot summers.
Some annuals such as marigold, calendula and sweet alyssum are commonly treated as perennials in south Texas because they can usually tolerate our moderate winters. Other tender annuals like zinnias and cosmos will be gone by the time winter is over. That being said, there are some hardy annuals which are often categorized as biennials, annuals, hardy annuals, tender perennials, or semi-perennials that can tolerate a frost but don’t like a deep freeze. These include the Laura Bush petunia, dianthus and snapdragons. If you hold out any hope to see these flowers next spring you will have to cover them, mulch them and pray over them and prepare to plant new stock in the spring.
It’s always good to complete these freeze protection tasks before severe weather approaches.
REMINDER: If suppliers run out of inventory in the run-up to a cold snap, you may get stuck using very thick cloth and bubble wrap.
“It’s a lot of work to cover plants for a hard freeze, and I don’t recommend getting sucked too deeply into it. When your hardy perennials get freeze-dried, leave them standing until mid- to late February so they can shelter the creatures who share your garden, as well as their own roots, and so their seeds can provide food for birds. It’s only another month and a half, and then you can whack them back to your heart’s content.”
~ Pam Penick, Cool Gardens in a Hot Climate (penick.net)
You can protect some freeze-tender plants with cotton sheets, lightweight blankets or cardboard boxes. But don’t rely on plastic, which can worsen cold damage where it touches plants. If you’re covering plants, make sure the sheets reach all the way to the ground and weigh down the corners.
Apply a healthy layer of mulch around your annuals. Mulch protects their roots from cold temperatures. Care for the plants well, watering and fertilizing them as their species require. Healthy plants are less likely to suffer permanent damage from frost than unhealthy plants.