So You Want to Put up a Hoophouse?
by Harriet Behar and Angie Sullivan

This article was first printed in the May/June 2010 issue of the Organic Broadcaster, published by the Midwest Organic and Sustainable Education Service.

Hoophouses are sprouting up like mushrooms (they can even look like mushrooms!) across the Upper Midwest.  Markets have opened for local foods, encouraging farmers to “extend” their season beyond what they could produce without this extra protection.  The investment in this infrastructure can have fairly quick payback, from both the higher prices “out of season” production can claim, as well as the higher quality and volume of produce you can reap from inside these structures.  The Natural Resources Conservation Service (a program within the USDA), has recently offered cost share dollars for the construction of unheated hoophouses or high tunnels (we will use the words hoophouse and high tunnel interchangeably). This support is in recognition of the controlled environment created within the structure, which can encourage more judicious use of fertility, pest and disease control inputs and result in the protection of water and soil quality, which is the key NRCS goal.

There are many excellent sources of information on how to construct a high tunnel, where to purchase a kit or how to put one up using a variety of materials you can buy locally.  Information on how to successfully grow a variety of crops within a hoophouse is also readily available and increasing every year.  MOSES, in partnership with the Minnesota Institute for Sustainable Agriculture (MISA) and the Institute for Agriculture and Trade Policy (IATP) recently launched the Midwest Season Extension website, www.midwestseasonextension.org. There you can find links to great Kansas State and University of Minnesota websites and listservs as well as many other helpful resources and the latest happenings in the hoophouse world.

Here we would like to run through some basic questions that you should consider, along with some ‘learn from our mistakes’ examples, to help you build a hoophouse that will be relevant to your operation as well as highly productive and flexible enough to keep you producing crops for years to come.

A Perfect Site is Key
One of the main decisions before putting up a hoophouse is site selection.  This decision should be based on soil type, soil fertility, full sun, good drainage and low weed pressure.   The more time you take to consider this decision, the more time you’ll save fixing problems later.   Hand-in-hand with site selection comes placement of your hoophouse.  Remember to place the hightunnel fairly close to your home.  You are planning to work in this structure during the cold months, the less distance you have to walk, carry your tools, equipment and your harvests, the better.
Level ground is a very important factor in building a hoophouse. You want your ground to be as level as possible, with no more than a 30% slope.  If you live on a hilly farm, like we do, this can be difficult.  Most likely, you already have a field where you are growing produce.  Don’t rule out that area for your hoophouse.  When we were considering site selection, we had it in our heads that we didn’t want to take up any ‘good’ ground we were currently using. Then the light bulb went on!  If you are already planting successfully in a field, you will be just covering it and extending the use of that field with a hightunnel.

Like any field where you would plant, you will need your hightunnel site to have good drainage. This is one of the most important aspects, second to site selection.  The last thing you want in the spring, when you are excited about working outside and getting your seedlings in the ground early, is to be dealing with standing water from melting snow and ice.  Nothing will delay your early planting more than beds that are full of water.  Water and snow running off the high tunnel, unless managed properly along the sides through either buried trenches with stone and drain tile or other mechanisms, could result in some very soggy areas within your structure. This can cut into your growing area, lead to disease, and damage your profits. 

If you plan to move the tunnel from location to location every few years, how much do you want to invest in this runoff management, and how can you design your structure site so it can be used as a regular field in the future?  Having buried rock and drain tile would not be disc-, field cultivator- or rototiller-friendly.   Landscape cloth or heavy mil black plastic might be one solution, perhaps even laid in a shallow ditch with a slight slope to carry away water from the sides of the hoophouse. This would still take some work to remove when you dismantle your high tunnel in the future, but would be less work than taking out rock and drain tile.  Still, if you plan to have the tunnel in the same place for many years, the better you plan for this water the less trouble you will have.  Ultimately, selecting an ideal site with land that slopes away from your structure will be much easier and much less costly in labor and materials than a highly engineered drainage ditch.
 
Equally important are the decisions about orientation and ventilation of the hoophouse.  The standard orientation is to have the center purlin run east/west.  This way you get the best light in the winter when the sun is low and you can have the long side of the hightunnel facing south to collect as much of the heat as possible.  But, you also need to consider your prevailing wind direction.  You would rather have the wind hitting a stronger endwall than hitting the side of your hightunnel directly.  A north/south orientation might not give ideal sun exposure in the winter, but not having your hightunnel blow down by prevailing north winds might be worth the tradeoff.  You will also need to think about ventilation of your hightunnel.  The NRCS cost share does not allow for electricity (or supplemental heat for that matter) in your structure. Hand crank roll-up sides are common.  Most plans come with instructions for how to make roll-up sides. 

Another factor to consider when deciding what type of hoophouse to build is personal comfort while you are working.  This is one of those things that many of us do not consider until we can’t stand up straight because we have been stooped over for too many hours working in our hoophouse. If you are building a hoop with straight sides, you will have more room to stand up and work in the outside rows. If you build a hoophouse with curved sidewalls, you will not have much head clearance on the edges.   Also, think of bed size and walking path spacing.  Our first year we wanted to use as much space as possible for growing so we could make the most money out of every square foot.  So we made our walking aisles about 12” wide.  This was a disaster, and made working in our hoop uncomfortable. Not to mention the lost produce when we lose our balance and step into our bed of $7/lb. salad greens.  Make sure you give yourself enough room to work comfortably.  Trust me, with the extra value your out-of-season produce will have, you can afford to give yourself enough space to walk and work between beds. 

Get the Soil Right
As in any situation where you are growing plants, proper soil prep is a must. Preparing the soil with cover crops and compost before you close it in gets you far ahead in fertility and soil tilth, and is much easier before than after you have the end wall up.  There will be some compaction of the soil while you are building the hoophouse, so consider how you are going to perform tillage to loosen things up once you have the structure “skinned.”  Some growers make it possible to remove an end wall so they can still get in to the structure with their tractor and tillage equipment. Others simply use a walk-behind, rear-tine tiller to accomplish their tillage needs.  We made the mistake of not considering this when we started construction of our hoop, and now get the pleasure of lifting the tiller through the doorway when it is time for bed preparation. Even a wheel hoe, push-type cultivating equipment or electric powered small tillers would suffice.  If you plan to use motorized equipment make sure you always use it during the time of year when you can ventilate properly.
 
How will you go about constructing your hightunnel?  Will you have the company you bought it from do the construction?  If you are one of these people, you will just get to sit back and watch. But, if you are like most people you will either be buying a kit that is going to show up in a box or you will be pulling together your own materials list and building the hightunnel yourself.  If you are heading down the path of self-construction, here is something you will want to remember:  Make sure when you are constructing the base of your structure that you are careful to get it in square.  Reach back in your mind to high school geometry and dust off your recollection of Pythagorean’s theorem (A2+B2=C2). In the long run, it will be worth the time to do this step correctly.   We will leave the rest of the construction process up to you and the manual that comes from the internet or with your kit.

Planning the Hoop to Fit Your Production
Another decision you will be making is what you want to grow in this structure.  Most likely you will be growing a variety of vegetables or small fruit crops to take to farmer’s market, put in a farm stand or for your CSA shares.  Perhaps you want to grow just berries and tomatoes: think this through, since they each need a different type of environment throughout the year.  Or possibly, might you produce a crop that requires you to remove the plastic through the winter and put back on in the spring?  Tree fruits or brambles may require freezing in order to maintain healthy production since moisture and fertility can be better controlled in the tunnel as well as the added protection against sunscald, wind, and frost damage.  (Yes, stone fruits such as cherries and apricots are grown commercially in high tunnels as well as blackberries, raspberries, etc.) There is a much higher percentage of number one fruit from trees and brambles grown inside a high tunnel rather than outside in the field.  These are all things to consider when laying out your beds and making decisions about spacing needs for your hightunnel.

If you are planning tomatoes or cucumbers, will the high tunnel be constructed strongly enough so that you can tie your plant trellises to the greenhouse? Or will you plan to build trellises that are free standing? There are many options for trellising depending on what you are growing.  This is where talking to other growers can be helpful.  They have many creative ideas about trellising.

Remember that for annual crops you cannot, under organic regulations, grow the same annual crops year after year in the same “field.”  This regulation is in place for a good reason, and the hoophouse is just like any other field on your farm.  Soil fertility and management are the foundations for healthy crop yields as well as pest, disease, and weed control.  Crop rotation is critical, so you need to consider what your rotations will be within that greenhouse, to both meet your market needs as well as promoting healthy soil and nutrient cycling.

Keeping the Hoop Productive
Maintaining soil fertility from year to year can be accomplished by adding compost to your beds along with any organic fertilizers and micronutrients. If you are growing many succession crops, you will need to keep amending and fertilizing your soil.  Amending your soil can happen in spring or fall, and in many cases is done throughout the growing season. Most of the work in the plant beds can be done with a tiller and different hand tools.  Adding at least 2 inches of compost to your beds in the fall or spring will add organic matter to your soil.  During the growing season you can till in the crop that is done being harvested and add more compost.  Adding to the organic matter in your beds will go a long way in preventing problems with salt build-up from watering and diseases that can be a problem in a hoophouse environment.  Consider short season cover crops such as oats or buckwheat in your rotation.

Do you plan that this hoophouse will remain in the same location for 10 or more years, or do you anticipate moving it (taking it down completely, not the moveable high tunnels on skids) to a different location?  If you are not planning to move it, you will need to consider how you will deal with salt build up and compaction of the soil.  How you lay out your rows from year to year and the type of watering you do will affect this. Drip tape will not compact the soil as much as overhead watering from a wand or sprinkler will.  By having permanent beds and walking paths, the risk of compaction to the soil is lessened and makes amending the soil easier. 

Water Issues Are a Critical Consideration
Whether you are growing many varieties of greens in early spring or late fall, single crops like tomatoes, cucumbers and strawberries or a combination of all of the above, one critical thing you will need to decide is how you will water your crops.  Drip tape, sprinklers, a hose? The most common watering method, it seems, is drip tape.  This is the most efficient way to get the water you need to your plants with very little waste.  With drip irrigation, generally one main hose runs the width of the hoophouse with lines of drip tape runing down the rows of each bed.  If you decide to use drip tape, it’s a good idea to get a timer on your hose spigot.  Too many times you turn on the water and get busy in the fields, or worse, yet forget you turned the water on and it runs all night.  If you have a timer it eliminates any worry about leaving the water on too long and lets your bad memory off the hook.  You can just turn it on, set the timer and forget about it.  On our farm, we do not use any landscape fabric or ground covering on our beds, so we do not bury our drip tape below the landscape fabric like some folks do. Because of this, we found we were constantly straightening and pulling our drip tape to keep it next to our plants.  This is especially true if you don’t use an anti-siphon spigot for your hose.  As the water is shut off, it will draw the water up and thereby pull your drip tape at the same time.  The easy fix for this is to use some landscape stakes and push them down over the ends of the drip tape to hold it in place in the beds. The other big advantage of drip irrigation is how clean it keeps your produce.  You don’t get sand & dirt splashed up on your produce like in an outside environment, which translates to easier post-harvest handling.

Sprinklers can work, however, you will need to be careful about the time of day you water. Try not to leave too much moisture on the leaves of your plants, as this will tend to lead to disease and fungus problems. Water early enough in the day to give your plants plenty of time to dry off and you should be fine.

If you are not growing through the winter, and only growing from late spring to late fall, you can probably get by with running a hose.  But if you plan to water in the hoop through the cold, snowy days of winter, what is your water source plan?  A large tank that serves your drip tape system with a stock tank heater might be one solution.  You would still need to fill the tank, but not as often during the winter.  Unless we have a lot of sunny days, you will probably only need to water once every 10 days or so.  Overwatering can be a problem too, since cold wet soil and plant leaves can lead to fungal problems.

Planning for Cold
Many hoophouses use no supplemental heat and are simply used for season extension.  However, there have been studies that suggest that keeping temperatures slightly above freezing can double production of winter salad greens, from two crops per year to four crops.  This is a decision you will need to make based on your own operation.  There are many options for heating hightunnels.  The NRCS cost share will not allow supplemental heat, so if you want to grow through the coldest part of the winter, perhaps planning for a secondary blanket of plastic or spun row cover over your crops would be a good solution.  Having purlins or anchors strategically set in place when you build your hoophouse will give you the flexibility to add this extra protection.  Remember too that the side walls will be colder than the center of the greenhouse, and it might be better use of your inside space to have your paths along the side edges (unless it is too short to walk there).  Stacking hay along the side edges may not be the best idea, since this offers great habitat for rodents. It is quite easy for them to then start making holes to move from their homes to their fresh salad dinners inside your high tunnel.

We hope you give some thought to these questions and that they help you develop the answers for your own situation and farm plans.  Take the time to attend field days or even just visit other folks who have high tunnels and see how they have dealt with these various issues.  You can learn a lot from what other farmers have developed and what they have decided was not satisfactory.  If you have an NRCS cost shared hoophouse, you must track how this is lessening your use of pest control products and protecting ground and surface waters from soil fertility product leeching.  Tracking these items will help you learn how best to use your high tunnel, both for fun and profit!

Harriet Behar is the MOSES Organic Specialist, and Angie Sulivan is the MOSES Resource and Events Coordinator. Both have diversified vegetable farms featuring productive hoophouses.