High Tunnel notes

Submitted by Ben on Thu, 03/26/2009 - 09:36

Last night the Emporia Area Local Foods Network (EALFN) held a class on "high tunnels" -- unheated, plastic greenhouses large enough to walk through.  Attendance was unbelievable -- some 70 people for a 3 1/2 hour class at dinnertime!  After an introductory video, we had two speakers from K-State's high tunnel project, http://hightunnels.org .  Here's what I learned:

  • Expect the "poly" greenhouse plastic to last 4 years in the midwest, then reuse it for smaller projects such as row covers or cold frames.
  • Don't worry about holes in the plastic -- it doesn't need to be airtight to work, and it is very tear-resistent.
  • Double-poly walls can be a good investment -- a small electric fan (or a wind vane, as some Amish demonstrated) can keep the walls inflated and make them much stronger and last longer, as well as raising the insulation value of the walls.
  • The researchers used manufactured arches which have grooves to attach the plastic using "wiggle wire," but plans are available online to use PVC instead.
  • Drainage is very important.  Don't put a high tunnel in a low spot.
  • Use drip tape for easy watering, but be careful when using tools such as hoes.
  • Beware of salt buildup from compost and other fertilizers; if it appears, you will have to leach it out.  The speakers did not feel that salt buildup from irrigation water is an issue in this area, unlike in Fairfield.  They say the local water will cause calcium deposits, which are not a problem for plants.
  • For a winter harvest of greens, plant by early October.
  • Raspberries and blueberries do very well in high tunnels, producing about 2x the yield as outdoors.
  • Most tomato blights are less prevalent in high tunnels than outdoors, with the exception of powdery mildew.  I think I heard them say that one recommendation for treating mildew is a spray of baking soda in water, but I find that hard to believe -- the effects on sodium and pH would be pretty drastic!  Need another source.
  • Strawberries are very popular to grow in high tunnels around the world, but not so much in the Midwest -- our summers are too hot.
  • Flowers are by far the most profitable crop to grow in high tunnels, but they require a lot of attention.
  • In the summer, install shade cloth, remove the end walls, and roll up (or down) the side walls.