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The Homeowners Column
A bit of cold weather returns to the garden
State Master Gardener Coordinator
For the past month I have been stuck in an oration loop in which I incessantly recite to anyone within earshot, "Well, you know it can still freeze". I knew technically it could still freeze since the average date of last frost is April 20 and the day of last frost is May 18, but after several days of summer temperatures even I was getting bored with my refrain.
Just to remind us we are not in charge of the weather, the looming prediction of cold weather arrived. So how did our plants fare? As with many things in life, it all depends. It depends on where your garden is located. City gardens with all the surrounding sidewalks and parking lots stay warmer than gardens in the wide open spaces of the country. It also depends on the plant species, the growth stage of the plant when cold occurs, how cold it gets and how long it stays cold.
Most of our perennial (non-tropical) plants such as hosta and peony can easily deal with short periods of 32 degrees. Frost hardy plants of lettuce, spinach, broccoli, collards, cabbage, peas, turnips and pansies laugh off the cold. The warm loving vegetable plants of tomato, squash, pepper, sweet potato, watermelon, okra, lima bean, eggplant, and cucumber can be damaged or killed by cold temperatures. If you already had these warm lovers in your garden, it is a wait-and-see game on how they fared after the recent cold. Damaged tissue will appear water-soaked and mushy. Sometimes damage is confined to the tip growth and plants will grow new leaves and stems. If the whole vegetable plant looks wet and slimy once it thaws, than it's time to replant.
Rhubarb and asparagus harvest is in full swing right now. If the leaves of rhubarb show damage after a freeze, the stalks should not be eaten. The calcium oxalate crystals that make the leaves poisonous can move into the stalks after a freeze. If the leaves look healthy, the stalks can still be eaten. If the leaves look soggy like cooked spinach, remove the damaged stalks and place in compost pile. As new rhubarb stalks appear this year, they can be safely eaten.
Frozen asparagus spears will be limp, dark and water-soaked with drooping tips. With eating frozen asparagus it is a quality issue and not a safety issue. Thawed spears will be mushy, but safe to eat.
Fortunately with tree fruits most of them in our area were past bloom. If temperatures stayed above 30 degrees F. the last few nights, little damage from cold should be evident. Here is a great chart of tree fruit critical temperatures from Michigan State Extension http://msue.anr.msu.edu/uploads/files/PictureTableofFruitFreezeDamageThresholds.pdf
Small fruits such as strawberries, grapes, blackberries and blueberries can also be damaged by cold temperatures. Strawberries are blooming right now. Critical temperature for strawberry flowers in full bloom is 28 degrees F. Most of the strawberry crop (at least 30 percent) is produced on the first bloom, often called the king bloom. Complete loss of the king blooms can be serious. Any blooms that are killed by frost will develop a dark center.
With grapes new growth may be killed at 30 degrees F. If new growth is damaged, grapes will often regrow, bloom, and produce about half a crop, depending upon cultivar. With blackberries and blueberries open flowers can be damaged at 28 degrees F.
For more information on critical cold temperatures on fruits and vegetables check out:
Fascinated by the weather? Join University of Illinois Extension Master Gardeners as Dr. Eric Snodgrass, UI Department of Atmospheric Sciences, presents "Weather Revealed" a look at practical weather analysis and weather forecasting on Tuesday, May 20, 2014 at 7 p.m. at University of Illinois Extension auditorium, 801 North Country Fair Dr. in Champaign.