Having the tools to grow past your first kill frost can open up a great opportunity for off-season sales in your area. Especially if your region is known for variable weeks of cold followed by an Indian summer, or a warm start to November or December. In my experience in central Virginia, we can extend fall crops and sometimes even continue to harvest some of the more hardy vegetables like cabbages into February or March.  

What Constitutes a Kill Frost?

Most fall crops will benefit from a short frost followed by a warm morning at the beginning of fall. Covering your crops too early may even attract pests to your crops. Often it is a bit of a guessing game and knowing your area. At my farm, we often get 3-6 degree unpredicted lows under the forecast. The best thing to do is to find a great weather app that shows you the hour-hour breakdown of the daily and even weekly weather to help you know when to cover. Generally, it’s time to cover those fall crops if you have more than 3 hours below freezing on more sensitive crops or if the low is 26 degrees F. or below that is also time to cover. 

What crops are more sensitive to cold? 

Frost tolerance can be different per crop depending on its stage of maturity. In regards to fall crops, our root crops such as carrots, beets radishes, turnips, and leafy greens like lettuce and arugula will experience cellular degeneration from too much frost. Meanwhile, a lot of brassicas such as collards, kale, broccoli, cauliflower, and alliums like leeks and scallions are much more frost tolerant. A 2-3 hour frost on these more tolerant crops is no reason to run out and put your row covers out unless you are worried about that unpredicted 3-6 degree low. So make sure you make a calculated decision and when you see lows of 26 or below or more than 3 hours of freezing and below it is probably a good idea to start covering. 

Can frost improve the taste of my fall crops?

Yes, absolutely. Cold-induced sweetening (CIS) in which extended temperatures at or below frost turn carbohydrates to sugars while protected from cellular degeneration with the row cover results in sweet veggies! CIS is a natural anti-freeze that vegetables use to avoid freezing and subsequent cellular degeneration. The stored carbs in the cells convert to sugars and act as a buffer, preventing water molecules from freezing. This conversion lowers the freezing point and will occur even under your row cover on frigid nights once you start getting into the lower 20s. Some of my favorite CIS occur in carrots, cilantro, parsnips, and daikons. Leaving us with phenomenal tasting produce that customers will naturally want more of!

What weight row cover works best?

There are different row cover weights per manufacturer. Usually, they are sold based on how thick or heavy the row cover is. My favorite weight is around 1 oz as anything heavier may help with much lower temperatures if you are north of Virginia. The heavier the fleece gets the less light transmission. 1 oz normally provides around 70% light transmission. 

The next consideration is how wide a blanket to buy for your bed space. Keep in mind what vegetables you want to grow and that you will be able to use this row cover in spring as well. On my farm, we have grass paths so we typically only think about 1 bed-top at a time. But if you have smaller paths then you could think about buying a wider row cover, such as a 10′ x 25′ or 10′ x 50′ 1.2 oz Medium White Anti-Frost Row Cover from Agfabric. This would be a great option to cover multiple rows with fewer sandbags to hold down the covers.

For just one bed, we would recommend a 5′ x 25′ or a 6′ x 50′ Anti-Frost Row Cover also available at Agfabric.

Now typically you will need a weight or staple to hold down the row cover, especially if it gets windy. I don’t personally recommend staples as this will decrease the lifespan of your row cover. We want to get the most out of these covers so that we are covering the cost of the fabric and making not losing money. Upnorth Sandbags are a great addition to any garden and you can space them 8-15′ apart depending on your skills to get that windward side nice and tight. If the wind can get up under your blanket it will! This is one reason we do not recommend hoops to go with the row cover. Another is that it is just one more thing to buy and again we need to consider our costs to be profitable. I am not convinced that adding the hoops plays a significant role in frost protection. While DIY Hoops make more sense for extending cool weather crops into summer or excluding pests as well.  

In conclusion

The initial cost of row cover may discourage a farmer from experimenting with late fall/winter crops. I have found late fall and winter to play an important role in retaining some of our favorite customers, by offering our products through the winter. If care is given to taking care of the row covers they will last many seasons!