CO-Horts Blog

Friday, September 4, 2020

Weather Rodeo

Posted by: Lucinda Greene, Arapahoe County Extension

The weather promises to be a wild ride for the Denver metro area starting Tuesday after Labor Day.  Remember the polar vortex in November 2014?  The bomb cyclone in March 2019?  The mini-polar vortex in October 2019, and the extreme temperature changes in February 2020, and April 2020?  By now, we are becoming familiar with the uneven weather patterns as seasons change along the Colorado Front Range. 

This weather can wreak havoc on the plants in the landscape.  Especially those you have cared for all season long!  Generally, if plants have been properly cared for, and are not under drought stress or pest or disease pressure, trees, shrubs, and perennials can handle these early frosts or freezes in September.  However, because we typically have another month before we put our vegetable and annual gardens to bed, you can take steps over the weekend to limit damage to these plants and still enjoy a beautiful fall harvest.

Pumpkins are a warm season vegetable crop that could benefit from being covered during an early season cold snap. Photo: Lisa Mason  

Follow these tips to give your plants a fighting chance to survive next week’s cold snap:

  1. Trees and shrubs – give all woody plants a good drink over the weekend or on Monday. The temperatures in the Denver area are expected to be hot – the high 90’s.  Trees and shrubs can handle the stress from a rapid temperature change better if their root systems have adequate water.  Moisture in the soil also helps moderate soil temperatures and helps protect plant root systems because water has a high heat capacity. 
  2. Perennials – give perennials a good drink like trees and shrubs.  Most perennials suited for Colorado’s Front Range (USDA Zone 5A to 6A) can handle these temperature swings. 
  3. Vegetables -  Depending on how cold it is expected to get in your area, harvest and cover warm season vegetables.  Frost cloths, bed sheets, drop cloths, or blankets make suitable covers for vulnerable plants including tomatoes, zucchini, peppers, cucumber, and squash. Use stakes to keep the material from touching foliage.  Remove the cover promptly in the morning when temperatures rise.  
  4. Vegetables – Depending on how cold it is expected to get in your area, you may wish to cover cool season vegetables like chard, spinach, kale, and lettuce. Root vegetables like beets, carrots, onions, and garlic should be okay without a cover.  
  5. Annuals in landscape beds – Cover with a cloth similar to warm season vegetables. 
  6. Annuals in hanging baskets and containers - Water the soil in hanging baskets and containers well.   Remove hanging baskets from their hooks, and store them indoors along with containers if possible, or group hanging baskets and containers together outdoors and cover with a cloth.  If containers and hanging baskets can be gathered together, store on the ground and cover, taking advantage of warm soil temperatures to keep air around these plants above freezing. 
  7. Finally, after this unanticipated early cold snap, take stock of your landscape.  Do you have frost pockets, or micro-climates that show evidence of higher than normal freeze damage, and therefore colder air accumulation?  Swales, or wide open exposures can experience colder temperatures away from sidewalks and buildings.  Consider moving desirable plantings to other areas of the landscape if you notice a consistent problem.  Or, consider choosing different plant material that withstands these inevitable temperature swings.  Native plants are a great option, since they have evolved in this tricky climate. 
  8. Call your local Master Gardener office if you have additional questions.  They are standing by to help! 



  1. I planted a few fruit trees last week. How should I cover them?

    1. Water well and add mulch at the base of the tree to preserve moisture. Keep the mulch 6" away from the trunk.

  2. What about rose bushes that have been established for two summers?

    1. Water well this weekend, and if not already present, you can add an even layer of mulch (2-3") around the base of the shrub. At this time, don't mound the mulch up around the plant as you might do to prepare for winter. That task will come later this season.

  3. In Loveland they're now calling for a low of 23. I don't think bedsheets or blankets are going to save my tomatoes, basil and annuals at that temp.

    1. Hi Pat-
      We totally agree! The forecast has changed significantly since the original post. Given a new colder forecast, warm season vegetables and herbs should probably be harvested this weekend. Hope the weatherman is wrong this time!

  4. I really appreciate the tip to assess the damage afterward. We are in a new house so this will be a good way for us to identify microclimates!

  5. I have cantaloupe climbing on trellises. They are protected somewhat behind them from a wooden fence. What type of covering would best protect the fruit already set? I have beach towels, quilts, sheets, and fleece blankets. I'm not sure which would be best for each type of plant, or if it makes a difference. I also have tomatoes, cucumbers, squash, peppers, lettuce, and corn. I'm not too worried about my root vegetables.

  6. I finally just got blooms on my raspberry bushes, anyway to save these?