It has become common for growers to purchase a DIY High Tunnel Kit, and ask manufacturers like us to design the structure so part functions as a greenhouse.
This means, the structure will be partially dedicated to in-ground planting, and part will be heated and dedicated to seed starting and propagation.
This often includes using interior partitions that vary in their level of complexity, as well as the addition of a heating element.
Design Elements for Multi-Purpose High Tunnels
The basic design elements between a standard high tunnel, and multi-purpose structure aren't all that different. Multi-purpose high tunnels still have these core features:
- Standard Ground Post and Bow construction
- Roll-up sides through their full length
- Single or double layer greenhouse plastic covers
- Single layer pliable plastic end-walls OR 8 mm twin-wall polycarbonate
- Standard entrance doors
Features Needed to 'Split' Your High Tunnel Uses?
First and foremost, 'splitting' your high tunnel for different uses will require two different climates.
Achieving these different climates is most easily (and inexpensively) achieved by installing a low-cost 4 year 6 mil plastic partition using snap clamps for attachment. This is likely the least costly method for creating two different growing spaces in your structure.
Once you have a partition separating your structure halves you will more easily be able to heat that section to the minimum temperatures required for seed-starting. This is mainly true because you now have less volume to heat, which will save you money.
If your partition is installed, and you want to install a walkway from the propagation-half to the high tunnel-half, you may want to have the ability to walk between sections. Here are some thoughts on creating passage between divided sections:
- Cut a slit in the center of your partition: Use inexpensive binding clips (like the kind used to hold potato chip bags closed) to keep the slit closed when not used. Make sure you have enough excess to 'bunch' the plastic up and clip it.
- Add framing: This is likely only reserved for people who want to make their partition more of a permanent feature for their structure. In this case you could actually frame a rudimentary end-wall in the middle of your structure. This means you could then install an ACTUAL door in your structures partition.
- A stick-on zipper or Velcro door: These are available out there, but we don't carry them because they usually have a very high failure rate (at least high for our liking). These might be available at hardware stores though.
Ventilation Considerations for Split-Use High Tunnels
So... you threw up a partition in your structure, and can now heat your seed-starting section much easier (and cheaper). However, when spring is in full-force, it might get HOT during the day... and FAST.
How will you manage to control temperatures in the propagation portion of the high tunnel or hoop house?
This is an especially important question to answer because your interior partition may not allow for easy end-to-end ventilating.
Here are some thoughts on controlling temperatures:
- Roll-up Sides: These are low-cost and come standard on most high tunnel hoop houses; these should help take a major edge off the interior temperatures. We have a post on the benefits of roll-up sides and how to install roll-up sides if you're seeking guidance.
- Peak end-wall ventilation: Even if you don't have electricity, you can do something to help remove hot air from your structure by installing a ventilation component in your end-walls at the structure peak. Aluminum Shutters with auto open and close wax cylinders are a great option.
- Exhaust Fans and Intake Shutters: Exhaust fans and corresponding power intake shutters are great. These are run by thermostats and requires electricity. While these would do well to remove hot air it should be noted that if you went this route, you need to make sure air can move through your partition. If your fan kicks on and doesn't have any air to pull, it will tax your fan motor.
Any air movement is better than no air movement when it comes to starting seeds.
For this reason, if you have the budget you may also want to consider HAF (horizontal air flow) fans. These help move air around the interior of your structure.
HAF fans are typically mounted to the truss-rafters or bows to help circulate air. This could help your entire interior environment NOT just your propagation portion of the structure.
Making the Propagation Part of your Structure More Permanent
You can make your propagation portion of the structure as legitimate or as simple as you wish.
This is the main reason more growers are starting to request split-use high tunnel hoop houses; they can avoid some of the permanent greenhouse elements that would otherwise result in a more permanent structure.
The above being said, some growers have tested their propagation portions for a couple of years and actually want to make those spaced more of a permanent feature of their structures.
Some growers make a more permanent propagation section in their high tunnel hoop house by:
- Laying gravel, stone, or a concrete pad in the seed-starting portion of the structure
- Installing a more permanent propane or natural gas heating element
- Installing a permanent drainage system in their floor
- Installing more permanent watering set-ups.
It should be noted that there might be permitting implications if you were to use concrete, or install permanent utility hook-ups.
Heating The Propagation Portion of Your High Tunnel
As mentioned in the above section... heating your structure may have permitting implications. Check with your local municipality before installing heating elements permanently.
With the above disclaimer about heaters mentioned, here are some options for adding heat:
- Electric space heaters: This is not the most efficient, but this is (believe it or not) a fairly common heating method for small farms that are diving their high tunnel or hoop house. After all, they are only heating a small portion of it.
- Modine propane / natural gas heaters: These are the most common type of heater for a greenhouse. They are mounted from the truss-rafters or set on a platform. They are made in various sizes and capacities for different size structures.
If you want to know what size heater you need for your structure, or want a quote on one of those Modine propane or natural gas heaters you an submit one of our contact-us form, and we could provide you a quote with shipping.
Get a High Tunnel or Hoop House Designed For Multiple-Uses
Whether you are fabricating your own structure, or looking to buy a high tunnel or hoop house, you should be able to plan so that it can function as both a greenhouse AND high tunnel.
Simply plan out the following before requesting a quote from a high tunnel supplier, or building your own:
- Plan out your interior partition: How large should the plastic be, and how will you hold it in place (snap clamps)
- Decide on your ventilation: Make sure you are able to regulate interior temperatures with roll-up sides, end-wall ventilation, and possibly HAF fans
- Plan how you will heat the structure: Whether wood burning stoves, rudimentary electric space heaters, or a more permanent propane or natural gas heater. Know what you want to do before building.
Of course it would be wonderful to have a dedicated propagation seed starting greenhouse, but when that isn't possible, a split-purpose multi-use high tunnel or hoop house might be JUST what your farm needed.
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