Preparing Your Oracle Garden for Cold Weather

By Catesby Suter

The first frost of the season came early this year, on 10/27/2020. That’s two weeks before Oracle’s average first freeze, which according to the National Weather Service, is 11/12. Because of Oracle’s location in the foothills of the Catalina Mountains and its hilly terrain, with plenty of low lying areas, temperatures are variable. Often a cold sensitive plant can survive in a sheltered area, or near a stone wall that holds the heat of the day. Every yard has microclimates, so it is possible that less cold hardy plants will survive in your neighbor’s sheltered garden, while these same plants, grown in a low spot in your yard, will suffer.

But you can help protect your plants by taking a few time-tested steps. The first step is to select plants adapted to your area. The United States Department of Agriculture has tracked temperatures and prepared maps showing the different climate zones across the country. These climate zones are determined by the average annual minimum winter temperatures, and each zone is divided into 10° increments. Because of our variable terrain, and depending on where you live in Oracle, your climate zone could be either zone 8 or zone 9. Zone 8 has minimum temperatures between 10-20° and zone 9 between 20-30°. Garden and landscape plants are typically labelled with their hardiness zones. If you are in doubt as to whether you live in a part of Oracle considered to be zone 8 or 9, chose zone 8, as plants adapted to this zone are more likely to survive the occasional harsh winter. Remember that the zones are based on averages, which means that there may be an occasional winter that is colder or warmer.

Most vegetables are grown as annual plants and are broadly divided into warm season plants and cold season plants. Warm season plants are frost tender; our early frost took out tomatoes, squashes, cucumber, pumpkins, beans and basil. Cold season herbs and vegetables include semi-hardy plants that can survive a light frost (generally considered between 29-32°F) and hardy varieties that can withstand the colder temperatures of a hard frost (25-28°F). Whenever a light frost is predicted in Oracle, it is best to prepare for the harder freezes, as local conditions vary considerably, and weather predictions aren’t always reliable.

Examples of cold-hardy (25-28° F) vegetables include:

• Brussels sprouts,

• Kale and collards which actually become a bit sweeter after a frost,

• Broccoli and spinach, and

• Garlic which is usually overwintered and harvested in early fall or late summer of the following year.

Examples of Semi-Hardy (29-32°F) vegetables include:

• Cabbage and Swiss Chard - if the outside leaves become damaged, remove them before harvesting.

• Arugula, leeks, mustard greens, cauliflower, and Kohlrabi can die when unprotected during periods of extreme winter cold

• Root crops such as carrots, turnips, and beets, are protected in the soil and can be harvested after a frost.

Additional steps to protect your plants from freezes and frosts:

• Using a row cover or an old sheet to cover your plants when low temperatures are forecasted (avoid plastic, as it is not a good insulator and if any part of the plastic touches the plant, expect to see frost damage.) If you have a translucent row cover, then the light will be able to penetrate, but if you use old sheets, be sure to remove them as temperatures rise, so your plants are once again exposed to the sunshine.

• Applying a 2-3” layer of compost to your plants in late summer/early fall and then apply a 3” layer of mulch, such as straw, or shredded bark. The nooks and crannies in the mulch trap warmer air near your plants.

• In a pinch, you can water your plants before a frost. When water changes from a liquid to a solid (during freezing) a small amount of heat is released. Often this is sufficient for the plant to survive.

Pay attention to your irrigation system during freezing weather. Make sure all above ground faucets and piping are insulated; you can purchase foam covers at most hardware stores. Remove your hose nozzles and release the pressure, as freezing water can burst your hose.

After worrying all summer about giving your plants enough water, it’s now time switch and start being concerned they are getting too much. Cool wet soils encourage fungal diseases that cause stem and root rots. Reduce the frequency of your irrigation and plan on checking in with your plants frequently to insure they are getting enough, but not too much, water. In the winter, most fruit trees do well with a slow, deep watering about once a week. Reduce water gradually and check your plants often. An easy way to determine if the plants are getting enough water is to check the soil. For bedding plants and vegetables, you can use your finger to verify that the soil, about an inch from the surface is moist, not wet and not dry.

For fruit trees and shrubs, you can check the depth of water penetration by pushing a narrow rod (1⁄4 to 1⁄2” in diameter) through the soil. When a tree has received enough water, the rod will penetrate easily to the 12” mark or slightly lower. If the rod slips too easily through the soil, or penetrates past 3’ and comes out wet, the soil is too saturated. When a tree isn’t receiving sufficient moisture, the rod fails to penetrate more than an inch or two. If that is the case, try increasing duration (how long), rather than frequency (how often).

Don’t prune trees and shrubs before the winter cold sets in. Pruning stimulates tender new growth that can be easily damaged by frosts and freezes. Wrapping young tree trunks helps prevent the thin bark of younger trees from splitting when warm days are followed by freezing nights. Both splitting and sunburning can occur in winter, especially when trees have a southern or southwestern exposure.

And don’t forget our feathered friends! Keep your bird feeders topped up and provide some fresh water. Even if the water freezes, there are generally only a few days when daily temperatures don’t rise enough to thaw the water. Wild birds especially appreciate fatty, high-energy foods (including sunflower seeds) during cold months. For hummingbirds, feeders will freeze around 29° F, so take them in if a freeze is forecast, or you might end up with a broken hummingbird feeder. If it has been more than a week or two since your hummingbird feeders have been visited, you can safely take them down. Tucson and Phoenix both have year-round hummers, but at Oracle’s elevation, year-round residents are rare. It is a myth that the presence of filled feeders will stop birds from migrating. The truth is that the urge to migrate is so strong that any birds that remain behind are likely not healthy enough to migrate.