Curiosities: Why are some crops planted in spring and others in fall?

Temperature sensitivity is the primary determinant in when crops can be planted, says horticulture professor Irwin Goldman. For most fruit and vegetable crops in Wisconsin, that means planting in spring. The more frost-tolerant crops — beets, kale, broccoli — can be planted earlier than those better adapted to warmer conditions, such as tomatoes, peppers and melons.

In general, “bulbs, roots, tubers and stems typically tend to be more cold-adapted and fruits tend to be more warm-adapted,” Goldman says. In addition to the extra steps — and thus more time — needed to produce a fruit such as a squash or tomato, it’s also likely that the fruiting plants co-evolved with insect pollinators, which fare better in warm weather.

For crops that can take the cold, fall planting can allow them to get established before winter, then take advantage of the moisture from winter precipitation to get a jumpstart on growing once things begin to thaw. For example, grains such as winter wheat and barley can be planted in fall then harvested in summer, when spring-planted grains are still immature.

In addition, some plants require a cold spell as part of their development, a process called vernalization. One example is garlic, which is planted in fall, Goldman says. “Garlic needs the cold to form the bulb.”