Timing Your Planting Dates for Earliest Spring Harvest
Overwintering entails establishing very young plants that can survive the winter and resume growth extra early the following spring. Once daylength increases to 10 hours, these plantings will grow rapidly.
Keep in mind that wide fluctuations in late-winter temperatures can sometimes cause overwintered crops to bolt before they reach a harvestable stage. This can be minimized by choosing varieties with greater bolting tolerance. (Our Good for Overwintering category, which includes varieties selected on this basis in our overwintering trial programs.)
The most calculated approach to scheduling seeding for overwintered crops involves seeding in the late summer to late fall, depending upon the crop. (Be sure to review the Overwinter Planting Chart for the crop-specific planting windows.) The correct timing will allow germination and the first stages of growth to occur before the plant goes dormant during the Persephone period. Growth will begin again when days begin to lengthen.
Another overwintering method involves sowing just before the ground freezes, so that germination occurs after deep winter, as daylength increases and temperatures warm. This method can result in a lot of dead seed, however, if conditions do not pan out. (There is a risk that a higher percentage of seeds will rot in the soil during cold, wet conditions.)
An additional strategy is to seed just as the ground begins to thaw, or just as the Persephone period is ending (so technically, this is not overwintering). This works well for direct-seeded spinach and brassicas. Only the top inch or two of soil needs to be thawed in order to plant the seed.
Scheduling Guidelines for Planting Crops for Overwintering
Ten hours of daylight
Use our clickable Overwinter Planting Chart to time your planting dates for earliest spring vegetable harvest.
Keep in mind that the planting dates are back-scheduled from the last 10-hour day at your latitude.
The number of weeks before the Persephone period is calculated for each listed crop.
The vegetable crops are grouped, as outlined in the chart key, to reflect their reliability for overwintering success.
What About Overwintering Flowers?
How to extend your growing season with cold-hardy annuals
After several years of research and trialing, we are pleased to share the results of our overwinter flower trials. Along with the Winter Growing Guide information here in Johnny's Grower's Library — which pertains primarily to vegetable crops — we now offer an extensive series of educational resources on overwintering flowers:
- Intro to Winter Growing
- Scheduling Guidelines for the Winter-Harvest High Tunnel
- Winter-Harvest Crops • Planting Chart
- Winter Production in the High Tunnel
- Overwintering Scheduling Guidelines
- Overwintering Crops • Planting Chart
- Protection Methods for Overwintering in Low Tunnels
- Focus on Crops & Varieties for Winter Growing
- Overwintering Onions from Seed