Planning the final harvest of storage and biennial seed crops based on temperatures
Temperatures at which to harvest:
35 Basil, Basil Seeds
32 Tomatoes, Peppers, Eggplant, Zucchini, Cucumber, Winter Squashes, Sunflowers,
Non-hardy flowers, Storage Onions, Beans
~20 Cabbage, Celery, Celeriac
~15 Carrots, Bunching/green onions, Turnips, Collards, Kale, Beets, Most Lettuces, Spinach
Ripening fruits such as tomatoes and peppers may appear unharmed after a freeze but the flavor will be compromised. The flavor is not as strong, maybe even bitter, and the texture is pithy. Tomatoes harvested from dead vines also lack much of their natural acidity and are therefore not recommended for canning or drying.
For storage and biennial crops, it is imperative that they are not exposed to temperatures at which tissue damage occurs. Winter squash and onions that have been frosted will develop a soft spot in storage which will rot first. Because they are above ground, they much be harvested before temperatures reach 32. Potatoes which have been frosted will also develop a soft spot, but because they are below the ground can be harvested when the ground is at risk of freezing. I dig them at about 28 degrees and no earlier.
For dry bean crops which are allowed to dry down on the vine, exposure to a frost before fully dry results in ruined beans. If a frost threatens before the beans are fully dry, harvest the vines and hang them in a well-vetilated, dry area to finish ripening and drying down. Dry pea crops can handle a light frost, but should be similarly harvested and hung if temperatures dip below 20.
Cabbages varieties vary in hardiness. Cabbages exposed to temperatures to which they are not hardy will develop a soft spot which will rot in storage. I dig at mine when the low is about 20 degrees.
Though carrot roots can handle down to 5 degrees, tops begin to die at about 15 degrees. This is relevant for storage because if the green tops are killed, the shelf life of the carrot is diminished. And if you are growing for a biennial seed crop the growth point for the new seed head is killed.
Mature celery and celeriac is much less tender than young plants, which can get crispy leaves at just below freezing.
Many dry and wet seeds will continue to mature after the mother plant has died. For tender wet seeded crops such as tomatoes, peppers, zucchini, cucumbers, and eggplants, harvest fruits and allow seeds to continue maturing in storage. For tender dry seeded crops like many popular cut flowers, seed maturing can continue and even hasten after the plants sustain significant damage from frost. I allow most to continue drying down in the field until ready to harvest, even after the nights begin to freeze.