Protecting plants in cool weather

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The ideas discussed in this article are relevant for mild winters. In severe cold climates some of these ideas may be applicable during the fall season before the deep winter freeze.
In El Paso the night time winter temperature can go down to 20°F. Our sunny climate and mild daytime temperatures help warm up the ground during the day but the soil temperature also takes a steep plunge at night with cloudless skies. In our otherwise mild winters, this is what is most damaging to the plants - the quick loss of heat on clear nights. Risk of frost is highest during these cold, clear, calm nights. Frost is less likely during cloudy or windy nights although it is not always a certain defense against frost.
Whenever it gets below 32°F most plants will need to be protected. Cold hardy annual flowering plants and vegetables may tolerate temperatures lower than 32°F but may not always be frost tolerant. Some plants, specially warm weather or tropical plants in containers will need more protection than others.

Identify frost tolerant microclimate areas in the garden/patio
Some areas in the garden may be more protected than others. Areas near large structures, tall walls, large trees etc may have more frost protection. Plants may get significant protection even by very minor changes in their microclimate. The principle behind any of these microclimate changes is minimizing the loss of heat from the plants. There is no artificial source of heat being used but rather, the effort is to hold on to as much heat as possible that the plants and soil have accumulated during the day.

Mulch
Mulching the plants is a very important protective measure against cold and frost damage. If the roots survive plant will revive next spring but if the roots are dead there is no coming back. Mulch the base of plants, whether in ground or containers, with compost or any other natural plant based mulch which can degrade easily without contaminating the soil.

Frost Cover

It is a synthetic light weight fabric that allows air, sunlight and rain to pass through yet slows down significantly the loss of heat from the plants and ground.
It can be left in place during the day if the days are cooler than 40°F. Frost cover should definitely be removed if the temperature is going to be more than 65°F. Between 40°F and 60°F the decision to leave the cover on during the day depends on wind chill, cloud cover etc.
Hold the cover down to ground with weights, bricks etc. Appropriate size clips from any office supply store could be used to attach the cover to wire hoops or container edges.
Here are some ideas for using frost cover

  • Move the containers in a patio during the winter. Arrange them nicely but close together. At night cover them all together with a large, wide frost cover. A size such as a 9 x 12 feet is quite useful for this purpose. Frost cover may be removed during the daytime.
  • For the most tender plants such as tropical container plants you may cover with 2 layers of frost cover and leave a single layer on even during the day. Open the cover on a sunny warm day about once a week for more ventilation, brighter sun exposure and watering the plants.
  • If in a small area of patio aesthetics and design are not a high priority you may consider covering the patio floor with black plastic and keep the containers on that. Black color increase heat absorption during the day.
  • Keeping water filled buckets among your plants and covering them all (plants and buckets) with one frost cover may have some additional benefit as water will also hold on to the heat.
  • For the plants in plant beds a frost cover may be directly spread on them without any hoops if their leaves are not soft and tender.
  • For small plants, seedlings and for plants with tender leaves it is best to have hoops made of either PVC pipes or thick galvanized wire.
  • The thick galvanized wire hoops are easy to install can can be stored away in small space in garage or garden storage after the winter. The hoops are made simply by cutting the wire and bending it into a hoop. When measuring the wire length to be cut for each hoop allow about additional 8-10 inches at each end to be inserted in the ground.

Burlap

Burlap will also provide moderate frost protection. It may not protect tender, small plants. It can be useful in dry weather but is not very useful when rain or snow is in forecast. Burlap gets heavy and soaked with water after a rain or snow and may result in some plant damage. The advantage of burlap is that it is a very environmentally friendly product and completely biodegradable if made of 100% natural fiber. You may consider covering the burlap with a layer of plastic during rain and snow.


Clear plastic
Plastic provides frost and winter protection but has to be removed during the day or the plants will get cooked in the sun. Plastic is definitely helpful during those severe cold spells with ice and snow that El Paso occasionally gets once every few years. Large plastic sheets may be bought at any home improvement stores, usually available in the paint supply section. The plastic sheet is layered over the frost cover for additional protection from rain and snow during 2-3 days of stormy weather. Leave the plants covered for few days till the storm passes. If the weather gets sunny but the temperature is still cold during the day, just remove the plastic layer during the day and leave the frost cover in place.
Store away the plastic after winter to be used again following years so less plastic goes in the landfill. Buy heavier weight plastic sheets which are not easily damaged in just one season.

NOTE: If the day time temperate is in mid 60s or higher, remove the frost cover or burlap. Cover the plants again in the evening around 4 or 5 PM. This helps in better heat retention as less heat is lost during drop in evening temperature after sunset.
If your plants are in an area which will get only 3-4 hours of sun you may leave the frost cover on all day. Burlap definitely needs to be removed during the day as plants will need light. Frost cover allows adequate light to pass through.




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Broccoli, cabbage, lettuce, spinach and other cold weather plants were under these hoops. Peas were grown against the bamboo support. The frost cover over the tall bamboo stakes is difficult to cover and uncover every day. It also takes quite an effort to keep this arrangement standing in the wind. This idea did not work well. The wire hoops however are definitely successful and easy to use during all winter months.

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Frost cover on wire hoops easily are able to protect the plants even during light snow fall. The plants are surprisingly undamaged. During the colder than usual freeze in El Paso few years ago when the temperature had dropped down to 2°F (picture not available) the plant protection arrangement was surprisingly successful. Two layers of heavy weight frost covers topped with one layer of heavy weight plastic were used to cover the plants. The plant bed stayed covered in snow and ice for 3 days. Chances of any plant survival looked slim. Frost cover and plastic were left in place for about 3 days. Then the plastic was removed and frost covers were left for an additional day. Only minimal damage was sustained by some plant leaves which were at the edge of the plant beds. Rest of them were in quite good health, unaffected by the chaos outside the hoop.