Sunshine Weekly Weeder Newsletter
6 January 2016
Mason Bees Class
Come out to the garden on January 23 at 11:00 am to learn about mason bees from Julie Morales, a local girl scout working towards her gold award. Julie will also be placing mason bee houses around the garden to hopefully help us attract these very beneficial pollinators.
A beige metal garden hose hanger which was to be mounted on a new post in Zone Two has gone missing from the tool shed. If anyone knows its whereabouts, please return it to the tool shed or call Katy Davis at 512-454-1291.
Frost and Freezing.
It seems that we may actually be getting a frost in the near future (if the forecasters are correct). The following is excerpted from an article by Skip Richter who was the Travis County Extension Director.
One of the great challenges we gardeners face each year is the threat of frosts and freezes
The Science of Frosts and Freezes
We all know that freezes can kill plant tissues but do you know how? When the water inside a plant freezes it causes ice crystals to form that pierce the cell walls of the plant. When the temperature warms up, the cells leak out their fluids as they die and turn to mush. Freeze damage first shows up as dark, water-soaked tissues which then turn black to brown and dry up.
Frosts on the other hand appear on the surface of plant tissues as well as on most any other exposed surface but not permanently damage the plant. During the night the plant surfaces radiate heat to the sky. When their temperature drops to the freezing point the water vapor next to it freezes on the surface. It is somewhat similar to the process on a warm day when water condenses on your iced tea glass because the glass is colder than the air.
Can you have a frost without a freeze? The answer is yes...and no. It is possible for frost to form when the air temperature is above freezing. Solid surfaces and plants lose heat faster than air on a cold night. Anything that reflects the radiating heat back down will prevent or at least greatly reduce frost formation. We use the terms frost and freeze to refer to different types of temperature-related events. Typically frost forms on a still night when the temperature drops to near or just below freezing. A freeze on the other hand refers to a more extended period below freezing and may or may not include wind.
Most of the time in the fall or spring season we gardeners are dealing with a marginal freeze where the temperature drops briefly to just below freezing at the end of the night and then moves back up above freezing soon after the sun rises. This is enough to destroy a fall or spring garden, but not a winter garden.
We can do a lot to protect plants from a freeze because the temperatures are usually not too low and the duration is brief. Hopefully there is also not much wind, thus making protective measures easier and more effective. On the other hand when a hard freeze hits with a strong wind and lasts for a day or more there is usually little we can do to protect our gardens. The wind displaces any heat that might have helped protect the plants and speeds cooling of plant tissues. Extended time below freezing makes our simplest protective measures inadequate to the task.
Keep in mind also that plants vary in their cold hardiness as they develop from seedlings to mature producing plants. Broccoli for example is quite hardy as a strong, growing plant but the flower buds, the part we eat, are much more sensitive to cold.
Plant Protection Techniques
If we can take steps to help our plants through those cold snaps we can cheat the hardiness zone a bit in the landscape and keep a vegetable garden going all winter long.
There are a number of techniques we can use to help avoid freeze damage to our plants. Here are a few of the more common ones.
There are ways that water can help protect plants. First of all plants under drought stress can be more susceptible to cold damage. By watering plants several days or more before cold weather threatens you can relieve stress if they are suffering from drought. Water is also a great "heat sink." That is, it holds warmth and releases it slowly, more slowly than plant surfaces or air. Watering your plants right before a freeze creates a source of warmth that will slowly lose its heat over the course of a long cold evening. This alone is not going to provide protection from a hard freeze but can be used with covers to make a small difference on a marginal night, and every little bit helps!
Sometimes all we need to do is keep a plant alive through the cold. The first parts of most plants to freeze are tender new growth areas and the areas between leaf veins where the leaf is thinnest.
Covering plants is the simplest, most practical way to protect against a frost or freeze. Keep in mind however that a blanket doesn't keep a plant warm, at least not to any significant degree. Blankets keep us warm because our bodies produce heat that the blanket helps hold in. if you wrap up the branches of a small tree or shrub you aren't doing it much good. These "landscape lollipops" as I call them are not effective. In fact they may keep some of the heat available to the plant away from it. The reason is that the main source of heat for a plant is the soil. On a cold night heat from the soil rises up around the plants. If you use a blanket to trap this heat within the plant's canopy you can make a very significant difference on a cold night.
When I talk about trapping heat I don't necessarily mean warm air, just air that is warmer than freezing. If you keep the temperature around plants from dropping below freezing you have accomplished your goal. Even cold soil is actually significantly warmer than freezing and thus a source of "heat" on a cold night.
To cover plants effectively, lay the cover over the plant and allow it to drape down to the soil on all sides. Then secure it with boards, bricks, rocks or soil to hold in the air. This is especially helpful in preventing a breeze from cooling things down faster. The next day, remove the covers to allow the sun to warm the soil surface a little and then replace the covers as the sun goes down.
I have used cardboard boxes and large round garbage cans to cover plants. Plastic sheeting or any material that radiates its heat out quickly will "burn" (actually freeze) plant tissues where it touches them. It also tends to not reflect the radiant heat back down as well. Plastic is good, however, in holding in the air on a windy night so if you cover the plastic with a blanket or sheet you can increase the amount of heat reflected back to the plant and soil.
Rowcover over hoops
Spunbound polyester rowcover fabric works quite well in holding heat. The lighter weight types are not as effective as the heavier types, which are generally sold as "frost blankets", but all types are helpful. I have set up hoop tunnels with PVC pipe stuck into the ground to form a series of arched hoops down the row. You can also drive short sections of rebar into the soil and then slide the PVC onto them. Space the hoops about 4 feet apart and attach another piece of PVC down from the top of the hoops for added support. The hoop tunnel is useful for preventing a tarp or other heavy material from crushing plants.
If it is going to get too cold for a simple cover to protect your plants, adding a source of heat beneath the cover can make a big difference. Anything that provides some heat is going to be helpful, especially if you have a good cover that is secured to prevent wind from moving the warmer air out from beneath it. One way to add heat is to place containers of water beneath a cover. This is most helpful when the plant is very small such as a new tomato transplant. Milk jugs work well. Place one or two jugs right up against a new transplant to provide maximum protection. The larger the container of water the more latent heat it can hold. Five gallon buckets are especially helpful if you can make sure the cover over the plant prevents air movement from outside wind and is effective in reflecting radiant heat back down.
What constitutes a Light or Hard Frost?
Light Frost = Temperatures 28-32 degrees F
Hard Frost = Temperatures below 28 degrees F.
Likely damaged by light frost: Beans, cucumbers, eggplants, muskmelon, New Zealand spinach, okra, peppers, pumpkins, summer squash, sweet corn, tomatoes, watermelon, amaranth, and winter squash (plants).
Can withstand light frost: Artichokes, beets, carrots, cauliflower, celery, chinese cabbage, endive, lettuce, parsnips, peas, swiss chard, escarole, arugula, bok choy, mache, and radicchio.
Can withstand hard frost: Broccoli, Brussels sprouts, cabbage, collards, kale, kohlrabi, mustard, onions, parsley, peas, radishes, spinach, turnips, leeks, and sorrel.
It is important to understand that temperature is not the only factor affecting survivorship of plants during a frost event. The further a plant or its parts are from the ground, the more likely it is to be damaged by frost. The ground is usually still warm in early fall and will radiate some warmth to plants that are close to the ground. Humidity can also help protect plants from frost. Humid air holds more heat and reduces the drying effects of frost. Air movement also has an influence on frost damage. When wind blows during cold nights, it sweeps away any warm air trapped near structures or the ground, eliminating their insulating capabilities.
Regardless of the protection from frost any temperature below 25 degrees F is dangerous territory for vegetable plants.
What to Plant in Early January
Asparagus crowns, Garlic Chives, Hrseradish, Parsley, Chervil
Officer and Zone Coordinator Contacts - Sunshine Garden
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