Frost exposure in Fall changes Brussels sprouts from somewhat bitter to buttery. The first harvest of sprouts I had before frost was tough and had a sharp taste. Now instead of springing them up to 28℉ nights, Brussels sprouts which have been exposed to frost are developing caramelized sugars that cheap, store-bought varieties lack in terms of flavour. There is timing and both science and art that will tell us we can expose them to the frost.
Frost Benefits
- Converts starches to sugars at 32-28°F
- Enhances nutty flavor compounds
- Thickens outer leaves for frost resistance
- Triggers antioxidant production
Protection Methods
- Cover plants below 20°F with burlap
- Use straw mulch around stalks
- Install temporary PVC hoop houses
- Water soil before hard freezes
Harvest Timing
- Begin picking 10 days after first frost
- Harvest bottom sprouts first
- Leave top sprouts for later frosts
- Stop harvesting at 15°F
Using burlap is a way to prevent frost burn from incredibly cold snaps. I drape the burlap over stakes to avoid placing it directly on the plants. Keeping burlap away from the crop creates an air space between the plant and the burlap itself. I used this method during last December's polar vortex event. The plants covered with burlap produced 20 lbs of sprouts; the uncovered plants froze solid.
As the temperature begins to rise, it is best to harvest your vegetables in full sequence to maximize your frost cycles. I typically harvest the bottom sprouts first, giving the top sprouts a chance to sweeten further. This staggered harvest method has tripled my yield. Keep unwashed sprouts in a perforated bag (it does not need to be a classic produce bag) for six weeks at 32° Fahrenheit, the flavors will keep intensifying.
The maximum amount of sugar conversion happens roughly 72 hours after exposure to frost. The best way to test this is to use a refractometer. Under perfect conditions, Brix can go from 6% to the 12% range, and my biggest batch has been 14%, or the sweetness of a candy store. This biochemistry is why gardeners fight for that first frost and eagerly go in the garden before breakfast when it's cold outside.
Read the full article: How to Grow Brussels Sprouts: Pro Tips for Big Harvests
