This time of year, the question for growers in temperate climates is not whether they will get frost—it is when and how strong! When it comes to frost in your garden and farm, you should sort out several principles and actions before the frost arrives.
Understand Plant Sensitivity
Frost kills tender annual plants, so it is important to know which annuals are sensitive. Families of vegetables like cucurbits are sensitive, but some more so than others. (Pumpkins are a bit tougher than melons and squash.) Tomatoes, peppers are also frost sensitive.
On the other hand, chard can handle light frost, and kale is totally fine!
Know the differences in crop frost sensitivity so you can prioritize plant protection when managing an approaching frost.
Determine Frost Severity
Severity of frost is a question of both conditions in the field and the surrounding environment. For instance, a frost warning comes into effect when temperatures dip to around 35 degrees F (2 degrees C), and certainly for anything around the freezing mark.
When frost occurs has very much to do with how long the ambient temperature stay this low. A severe frost that is very damaging to crops like pumpkin would be caused when the temperatures stays low for many hours at night. It is important to note that if it is cloudy or windy, even if temperatures enter into danger zones the frost won’t be as severe or may not occur.
Moisture also has a part to play. More moisture in the ground will take up the cold before the vegetables freeze.
Watch the Weather
This time of year, I have my phone’s home screen set as a screenshot of the weekly forecast so I am reminded to check the updated online forecast on a daily basis. I can plan days ahead of time and stay ready to act at any moment to take my garden into hand for frost protection!
I use reliable weather forecasting sites like Environment Canada (because I live in Ontario) instead of generic weather sites (like those preinstalled on your phone). Growers in the U.S. can check out the National Weather Service for forecasts.
What You Can Do
There are several ways to manage a looming frost based on your goals.
Harvest or Protect
First, harvest long-season crops that are frost sensitive before the frost. This includes bringing in your haul of winter squash or all your tomatoes for processing into sauces. In some cases, you may even want to bring in green tomatoes and have them ripen inside for a further increase in crop yield.
In other cases, the crop in question cannot store and must be protected for continued harvest. This would apply to (for example) a patch of chard that, if protected through a minor frost, can continue to flourish for weeks, a month or more.
So, basically, either harvest before the frost or protect against it!
Protect Crops to Gain Growing Time
It is important to note that, if you can protect against the first frost, you often end up with increased growing time. Covering crops like squash or tomatoes can give you more time to finish ripening.
It is also important to remember not to prioritize harvest and protection of crops that don’t face frost threat (or, in the case of some plants, actually benefit from it). Carrots, for example, grow sweeter in the fall after a touch of frost!
Needs & Haves
For protection, ask yourself how big an area you need to protect, and what do you already have for supplies?
Commercial growers use field row cover, which lays out nicely over entire beds of crops. The homesteader may simply decide to save old blankets and duvets, using them to cover a patch of tomatoes or chard to protect from overnight frost.
These blankets provide a lot more frost protection than a field row cover. But of course this isn’t practical for a 100- or 300-foot market garden bed!
Use Moisture for Minor Frosts
It is also possible to use a sprinkler system to reduce the frost impact, taking up cold into the humid air rather than freezing crop flesh.
This is a good solution for minor frost. But it won’t be enough for a heavy frost that sits on the ground for a long time.
Design Against Frost
It is also important to note that you can plan your garden layout for a reduction in overall frost.
Gardens set higher up will allow cold air to sink away in the coolest hours of night. But gardens down in a low spot (and especially if the wind is blocked by a building) will collect cold air, allowing frost to pool for hours in the early morning.
I hope these frost tips will serve you well to get more out of your garden.