FREEZE PROTECTION ALERT
Citrus and subtropical plants throughout the south and southeast Texas are sometimes vulnerable to the temperatures which can be predicted as a very severe arctic freeze rushes into the area. Homeowners cannot assume that cloud cover will hold nor can they assume that the predicted minimum temperatures and durations will not be reached.
Do not rush out and harvest all of the mature fruit on your trees unless you do not plan to protect the trees or unless you cannot adequately protect the fruit. A rule of thumb is that it takes about four hours at 27 degrees to form ice in grapefruit (sorry, we have no conventional wisdom about satumas and other mandarins).
Do not wrap the trees up like you would a child since such efforts prevent radiant heat in the soil from reaching (and warming) the tree and fruit. Instead, drape tarps or blankets or similar material over the tree, pull the comers out tight and stake them down like you would a tent. The idea is to cover the top of the tree and as much of the surrounding ground as the cover permits. In this way, all radiant heat released from the soil beneath the overhanging cover will remain in that area, bouncing back and forth all night long to keep the trees from freezing. The tie downs are necessary to keep the covers stretched outward and to keep the expected strong winds from blowing the covers off.
Young, small trees can be banked with clean soil, as high as you can pile it around the trunk. In addition, banked trees can also be covered for additional protection.
Water thoroughly immediately, as wet soil can absorb more heat for subsequent cold protection.
Heat sources can be added beneath the covers for the ultimate in freeze protection. Incandescent lights are very good for this purpose. Be careful with the electricity, as the ground will be wet and there may be precipitation associated with the freeze. A pump-up type of gas lantern will burn all night, though you�ll have to pump it up again about midnight (just set it on the ground beneath the tented tree). The propane lanterns will also work if the propane cylinder will last long enough.
In summary, water thoroughly immediately, stretch covers over the trees (and tie them down at the corners) and prepare supplemental heat sources for use.
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