Plastic hoops for early spring harvests

Early spring vegetables grown under plastic hoops

Even in central US you can harvest early spring greens from seed sown in late summer the previous year. The photo above was taken March 21. We’ve already made a cutting of radichio, spinach and chard. Also growing in the photo is butterhead lettuce, a red leaf romaine and a feathery leaved anise.

Granted, we had a pretty mild winter this year. So maybe we just got lucky. But our experiement was successful enough to re-double our efforts next year.

Below is a photo from March 9 of this year – barely past February! We are doing some very early weeding – the down side to growing through the winter…

We have had good success growing vegetables through the winter in Iowa
We have had good success growing vegetables through the winter in Iowa. Although leaves die, the plant lives and jumps to life witht he first warmth of early spring.

The system is simple. We prepared the beds and planted a variety of seed throughout September. To hold the PVC hoops in place we drove rebar at an angle into the ground and slipped the PVC pipe over the 6 inches or so of the rebar we left protruding from the ground. Normally one would use a UV protected transparent plastic of the type you could buy at FarmTek, but here I used the heaviest of the clear plastics I could find at our local big box store. This is not a durable solution though as this non-UV protected pastic will degrade in the sun. Thankfully winter UV levels are apparently quiet low in Iowa, so maybe the plastic will last a couple years.

I left the hoops uncovered to facilitate weeding, thinning and watering until hard frosts threatened. Even when I did finally pull the plastic over the hoops in October I would leave the ends open and/or pull the plastic off again on sunny or warmer days.

Clear plastic does an incredible job of trapping heat from the sun. The small areas unde the plastic heat up very fast once the sun hits them, even when the air temp is chilly. It has taken me a couple years to get familiar with this process. A very valuable tool is a digital thermometer with a remote sensor unit. Put the remote sensor into a plastic zip-lock baggy to keep it dry and clean. Put the reciever in a window where you can easily monitor the temps under the plastic.

We planted carrots and beets, cilantro, chard, leaf, butterhead and romain lettuce, mace, spinach and radishes. We harvested radishes and cilantro through the winter. It doesnt look like the carrots survived, although this year we’ll plant them in August and use the hoops as an in-ground storage. We’ll pull them as needed through the winter. Lettuce and other leafy greens die back with the cold, but the plants live, and jump to life with the very first rays of spring sun!

Its important to remember that once covered your planst will rcieve no moisture. So monitor ground moisture and water if needed. We didnt need to at all this year. You may well need to re-cover the hoops in the spring if temps are forcast to dip well below freezing. I would recover for temps below 25F, or if the cold spell was to last for days.

Finally, this year we will use wood shavings as a mulch to keep weeds down and to create a layer of protection. I may use a ReMay type floating row cover to assess the cost/benefit of it.

Spring vegetables grown under plastic
Spring vegetables grown under plastic. Central Iowa, March 21st