I’m planning to convert a small portion (maybe 8x18’) of my unheated hoophouse to grow some perennial fruits and berries. I’m doing my best to leverage this growing space and diversify. I currently do winter and summer veg and plan to continue that, but would like to expand the variety of fruits I grow. I’m located in south-central Iowa, zone 5A. My unheated hoophouse is likely a 7A. The challenge being that much like outside the tunnel there are some late frosts, coupled with heat spikes in early spring that would likely coax early-bloomers to bloom too early (though I wish I thought it would be worthwhile to grow pluots and interspecifics). Also, I don’t want to waste valuable space growing things I can grow outside the hoophouse unless it really extends early or late-season harvest.
So far I’m planning on adding 5 vars of blackberries (which aren’t reliably hardy outside for me), a few strawberries (so I can hopefully get berries a month early), maybe even a few asparagus for early harvest. I may put a fig in the ground in there knowing it will need pruning and may occasionally freeze back. Possibly a Salavatski pomegranate? Anything else folks would recommend? I’m at a bit of a loss here…
My thought is an unheated hoophouse isn’t likely a Z7. It will get just as cold at night on coldest days as outside. Then during the day it will be much warmer. Those violent flutuations will be very hard on things like figs. That’s not based on firsthand experience just my judgement.
You could try pluots which will take zero or probably -10F. I’d heat for those to hold zero on coldest nights. And then heat just enough in spring to avoid freeze damage. That won’t be very expensive of a heating bill.
Thanks for the response. I did say “likely” a z7A, but I’ll concede that was too strong. I don’t know for sure. I have intended to get a min-max thermometer to test this, but all I can say is it NEVER gets as cold in the hoophouse as outside (not that there’s any significant insulation but its always considerably warmer during the day and moderately warmer at night). Here’s just a single data point, but I think its telling. On our coldest morning last winter when it got down to -18 outside, hoophouse was +4 at dawn (and +28 less than two hours later while still at least -12 outside). Another thing is there is likely quite a bit of temp variation depending on where in the hoophouse my thermometer is placed. Anyhow, it certainly may not be z7A, but I feel pretty confident it is at least a z6A. But I’ll only know for sure when I order min-max thermometer!
I have no intention of actively heating it at this point. My ‘passive’ heating includes keeping my 20 laying hens in there during the winter, along with 3 full IBC totes of water (that’s 825 gallons), and a couple yards of pseudo-active compost. Those 3 things make a difference, though I can’t be sure how much. I neither designed nor built this hoophouse.
I agree the diurnal temp swings are violent, but my winter salad greens, carrots, cilantro and perennial herbs handle it with aplomb (though there is zero growth from Dec thru Jan). I’ve already ordered the blackberries, and the strawberries, asparagus and fig(s) are free for the transplanting so I don’t really have much to lose there. I’ll start with that, actually measure my temps next year, then build from there. Maybe I’ll even consider adding a hardy kaki persimmon, if I can keep it pruned to 8 ft!
Thanks for your thoughts, I’ve learned a lot from your posts and experience.
My greenhouse which is 32x54x16ft tall and covered with a double inflated layer of woven poly won’t maintain anymore than 1-2F warmer inside than out. With one exception on cloudy nights I’ve seen +6F warmer inside. So I’m skeptical of a +22F temperature differential absent massive passive heat mass or one of those structures heated by circulating air under ground.
One member on here claimed a similar differential. I found out later the lean too structure was open to his garage. That means it was being heated by the garage/house. That’s not an unheated structure.
Would you be willing to share your experiences (successes and failures) on growing in your tunnel during cold weather? In this thread or a new one? I’m in zone 5 as well. I would be working on a mini scale, but I’d like to hear what’s possible.
I inherited the use of this greenhouse from my mother-in-law when we moved to the property 1.5 years ago. Its 30x50x10ft double poly detached from any other structure by 20ft. It is on a very, VERY slight south-southwest facing slope. There is no active air circulation. The long axis runs NE-SW which I would think is less ideal from a passive solar gain perspective than E-W. There’s a 6x30ft concrete pad along the NE end. The soil is good Iowa black dirt. I use a crappy old thermometer though I’ve never had any reason to doubt it. I keep it out of direct light and towards the middle of the greenhouse. However, it may have been propped up on the ground and there may be a fair amount of heat radiating out of the soil by morning on a cold night.
All I know is my Aug-Nov seeded lettuce, spinach, arugula, carrots, cilantro, parsley, turnips, kale, broccoli survived the winter and continued growing once warmth and light increased in February. The only thing with the veg is they got covered with Agribon 19 row cover for most of Dec-Jan (per manufacturer it provides only 4 degrees of frost protection). The -18 degree night caused some cold damage to the broccoli and cilantro, and I lost 5-10% of those plants, the remaining broccoli and cilantro recovered. No other plants suffered any damage all winter.
Our extreme minimum this winter so far was -8 - -10 (though I didn’t check to see what the thermometer in the greenhouse read). There has not been any cold damage to plants in there this winter. I did cover my rosemary with an old towel. It was undamaged.
You’ve got me curious though. I need to get a min-max thermometer so I have a better picture of what’s going on in there. Cheers.
Not much to tell really. I read Elliot Coleman’s Winter Harvest Handbook and been trying to put it to use. Its been surprisingly successful. I’m still working out ideal planting times. Like Elliot says you are extending the HARVEST season more than the GROWING season. Plant LOTS if you want to eat salads all the time. I only ended up harvesting a big salad a couple times a month in Dec and Jan, and realized I needed to overplant this year. Then in March when its going gangbusters your friends and family will be impressed by all the produce you’re giving them and they haven’t even started planting outside. In addition to the list above, I also had chard, green onion, wild arugula, mache, claytonia, daikons and other winter radishes planted and the only thing that suffered any notable cold damage was broccoli and cilantro. I saved the seed from the surviving cilantro and have that sown this year, but its been relatively mild so far.
When I lived in Colorado I had a few cold frames and they worked wonders in that milder and sunny winter climate, but midwest winters would be a hell of a lot harder on me if it weren’t for the hoophouse!
It’s possible I suppose that 6x30 concrete pad could have coils running under it that circulate water for warming. Then again in the old west rocks around the fire ring were later rolled under the campers blanket to keep warm because rock holds heat well which is likely with concrete too. The old timers I’m told backed their model Ts up a manure pile so it would start the next day. There are lots of days to keep things warm that are not obvious. Fruitnut is right something does not seem right. Having said that when I was a kid I lounged on the south side of the house at times in the sun because in the winter there is not s warmer place to be. Back to the original request on what to grow which is what I heard of high tunnels being used for in Iowa originally was peaches. Blackberries you can grow now but peaches are a premium at times in Iowa. Fruitnut would have good advice on figs etc. Maybe cold hardy Chicago so if temps plunged one night the loss would only be growth and not roots.
Please let us know when you get the max/min thermometer and collect some more information on how the inside temperature compares with the outside temperature. It may also be interesting to collect some information on how much the water temperature in the IBC totes changes
I noticed you mentioned that you have 825 gallons of water in the high tunnel which probably helps with the temperature swings. Thats about 6600 pounds of water which has the ability to store 1BTU for each pound of water for each degree of temperature increase. Just a 10 degree change in water temp would store over 66,000 BTU.
I have always wanted a high tunnel, but was reluctant to take on another project. Please let us know how everything works out.
Nope. Its just a simple concrete pad. My MIL and FIL built it some years ago and confirmed this.
My thoughts exactly.
Well, I would be concerned that peaches would be coaxed into early blooming moreso than outside the greenhouse, but I’m starting several pits of a local variety that I could graft onto as a rootstock and try next year risk-free.
I’m no greenhouse expert and its a very basic structure so I’m inclined to doubt my old thermometer, but regardless of numbers I’ve sure been impressed with the results. Hopefully, my redesign and adding a few perennials helps me more fully leverage this great resource!
Yeah, Ericka lives just down the way from me and was my source for these peach seeds. My MIL has had good success growing peaches on the property. They seemed to produce well for her at least every other year, though were fairly short-lived. However, she provides ZERO care for her fruit trees
