Winter is setting in and the frosts begin to descend upon the gardens, which brings unique challenges to the garden. The lettuce leaves turn their translucent shades of colors. The broccoli head looks like a glistening star. Collards offer a frosty accent to the landscape and some of the mustard greens look almost mushy in appearance. Farmer Nathan has some insight to share with 5 tips for harvesting around a frost.
Tips for harvesting leafy greens around a frost
Freezing. That 32 degree temperature of fate for many vegetables. If you see a chance for the night cold to reach freezing or colder, it is important to know when it is safe to harvest your produce. Especially when it comes to leafy greens. (If you are curious about when your first frost is, check out the Farmers Almanac!)
As the thermometer dips 32F or below in the morning, watch for any signs of frost before you begin to harvest your greens. I like to walk around the perimeter of the garden the day before a predicted frost as the footprints will be the first place for a frost to settle. In normal conditions, this will give you about 5 minutes of warning before the frost settles. Once you start to see the glistening signs of a frost, it is best to wait on harvest to prevent damage.
In cases where a hard frost (colder than 24 degrees), I like to hold off on harvesting or disturbing the plants until the temperature warms well above freezing. With many of the greens we grow, at 24 degrees icicles will actually begin to form on the leaf as the moisture is pulled from the leaves by the frost.
Avoid harvesting frosted plants
What happens if you harvest a frosted plant? First off, the water inside of the leaves has expanded, which doesn’t cause damage in itself. But if the plant is disturbed during this critical phase, there is a chance that the frozen cells could burst. This can cause irreversible damage to that part of the plant. In other instances, the frost causes the water to move towards the surface of the leaf, leaving the center fragile. In this case, a harvested leaf or plant would deteriorate quickly. Either way, I suggest avoiding harvesting most plants if possible when there is a frost.
Harvesting around a frost – afterwards
I generally like to postpone the harvest until after the frost has lifted. This can take a bit of time and careful observation needs to be made to ensure no damage is done to the crop. Harvest too shortly after a frost and the produce will turn to mush. At the same time, waiting too long after a frost (especially hard ones), and the crop may dry out as it tries to regulate the moisture levels. This is especially susceptible with leafy greens like lettuce or arugula.
Post harvest: handling leafy greens
If you have plants that has been damaged by frost, some damage is irreversible. This can sometimes be in the form of frost burn on the tips of leaves. Leaf spotting due to pockets of moisture that didn’t properly evaporate causing decay or lettuce drop. Or in some cases cause leaves to fall off due to cell walls that have exploded due to the water molecules expanding. For the longevity of the crop, I like to remove any damage that has the potential of spreading to other parts of the plant or spread diseases amongst other neighboring plants. Sometimes this is via a harvest and other times a spot removal of affected plant material.
When harvesting a crop after a frost, moisture is important to prevent the crop from drying out. I like to get any greens harvested into cool water within 20 minutes to help them absorb the water they need and crisp up. With root crops, simply spraying them off with cold water achieves the same goal. But don’t over do it, as there is such a thing as too much moisture. I like to follow up the water bath by placing the produce in a refrigerator with the greens exposed to the air to dry out for a bit to help extend their shelf life.
When to harvest root crops around a frost
Root crops tend to not be affected as much by frosts. This is especially the case with carrots, which can actually be harvested frozen and thawed out to use fresh. Most other root crops such as beets, turnips, and radishes like the same treatment as leafy greens for the longest shelf-life. Sometimes, I will top my carrots before a hard frost to keep the energy in the roots while using the earth as a cold storage. As long as you keep the carrots covered to shed any snow, all of those carrots can stay fresh throughout the winter for fresh eating right in the ground!
Tools to expand the harvest period
I love to use frost blankets to help keep the frost off the leaf surface of the crops. This helps buffer the air temperature while lifting the frost from the plant and onto the blanket. It doesn’t work 100%. But they definitely help build a small buffer in the winter garden. One thing to note is if the fabric is touching the surface of a plant’s leaf, it can actually cause worse damage. This is due to the cold transferring to a pinpoint location on the plant. I have lost a good number of crops to this, which is a casualty of winter farming. Check out our other post on protecting your garden from frost for more details on how to cover your garden.
Straw is a decent insulator for the garden. When spread overtop of some crops (such as turnips or beets), it can actually help insulate the crop from cold weather. This can help lessen some frost damage enabling a larger percentage of the crop to become harvestable. The downside is it takes time to both lay down the straw while also making the harvest period a little more messy.
The benefit of using mulch
Mulch plays another great role in the winter garden. I use it to help the soil hold more moisture. Soil with more moisture holds more heat than dry soil keeping the soil warmer. By mulching our rows, we have seen less frost damage and better management of our crops during the frosty months. And my root crops soak up the added heat by growing faster.
I also like mulch as it keeps the soil much looser. This allows for better transportation of nutrients and water throughout the plant’s root systems. Loose soil will also not stay as cold for as long as oxygen molecules can move around more readily. It acts like a blanket buffering the soil from the harsher cold temperatures.
I hope these tips for harvesting around a frost are helpful to you. may your gardens grow bountifully and help lead to a healthy & happy life.