Mar 2, 2018
With proper approach, growers can supply fresh products year-round

Spring is upon us in Michigan and we have emerged from the Persephone Period, which is the time of year when days are shorter than ten hours (day length calculator). As the days get longer, plant growth rates increase in response to boosted photosynthetic activity and warmth. As growers head to their hoop houses to harvest and seed, they may encounter crops at varying stages of production. In this article, we will discuss the difference between winter and overwintered production of cold season hoop house crops.

Winter production

For winter production of cold season crops, the goal is to time the planting so the crop is at a harvestable stage by the time day length drops below ten hours and the real cold sets in. Due to the ranges of days to maturity across different crop types, seeding dates will vary, so the best way to determine appropriate seeding dates is to run trials. Using standard production methods, seed a new succession each week after finding an appropriate range of dates. Keep in mind that each year will be slightly different, but keeping good notes on seeding and harvest dates will help inform future production decisions. In northern Michigan, winter crops are typically planted into the hoop house between late July and early September depending on the crop.

If appropriately timed, winter harvested crops will reach maturity as the growth rates begin to decline due to cold temperatures and reduced light levels. With the proper crop protection (row covers or supplemental heat), crops can be held in the hoop house for wintertime harvests. Using this approach, growers in northern Michigan can often extend the harvest window for more tender winter crops into mid-December and hardier crops extending into February.

Overwintered production

Overwintering of crops allows for early spring harvests of crops planted late in the fall. Growers should not expect to harvest these crops until growth rates increase in the spring. The primary advantage of this production method is that the crop is established in the ground waiting for ideal conditions before resuming its growth and reaching maturity three to six weeks earlier than a spring sowing. The disadvantage of this production method is that it ties up hoop house space throughout the winter months, reducing winter income potential.

Similar to winter harvest production methods, the best way to determine optimal dates is through production trials. The goal with overwintered production is to sow seeds early enough so that warm soil temperatures will encourage uniform emergence, but late enough so that the crop enters the Persephone Period with two to three sets of true leaves. If properly timed, these young seedlings will have a better chance of surviving the cold winter months. In northern Michigan, typical overwintered seeding dates will range from late September to late November depending on the crop.

To successfully overwinter crops, selecting cold-hardy varieties that will be able to withstand the subzero winter temperatures is critical. Row covers or supplemental heat can increase survival rates, though careful analysis of inputs is important to determine whether an overwintered crop is profitable.

Crop options

Which crops are selected for cold weather hoop house production will depend on production methods, market demands and grower preferences. However, there are crops that are better suited to these production methods than others.

Many growers rely on cold-hardy greens to provide income throughout the winter months. Spinach is likely the easiest to produce using overwintering and winter harvest techniques due to its extreme cold tolerance and familiarity. Lettuces and brassica greens are also commonly grown, though cold tolerance is variety specific. Root crops, such as carrots, beets, turnips and radishes also perform well in the winter hoop house, though some do not overwinter well in Michigan without supplemental heat. Some herb varieties, such as cilantro, parsley and fennel, can be grown into the winter, but may need supplemental heat for overwintering.

When properly managed, a mixture of winter and overwintered production methods can yield a constant supply of cold-hardy crops for sale and consumption throughout the winter, leading to increased revenue, balanced cash flow and increased customer retention. With careful variety selection and proper crop protection, Michigan growers can eat fresh year round.

–  Collin Thompson, Michigan State University Extension

Photo above: Northern Michigan hoop house in winter, including both winter harvested and overwintered crops. Photo. Collin Thompson, MSU Extension





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