I know it’s only January but I am thinking about a greenhouse or something so I can extend my growing season for vegetables. Any suggestions? AL

In Oklahoma we have a fairly long growing season, but once you get used to eating fresh vegetables from the garden, it’s easy to miss that during the cooler and winter months.

There are basically 3 approaches you can take to extending your growing season: low tunnels, high tunnels, and greenhouses.

Low tunnels are constructed of hoops of wire or pvc, bent in an arch over your crops and covered with a fabric or polyethylene plastic to essentially create a small little greenhouse. Low tunnels will give you a couple of weeks head start in the spring or a similar extension of the growing season in the fall. These are not heavy-duty structures and are typically built in such a way that they are easy to take down when no longer needed. On surprise cold nights, a blanket or an additional layer of plastic or garden cloth can be added to keep them safe. Many gardeners use these low tunnels each year with good success. You might want to start here to see how it goes before investing money in a high tunnel or a greenhouse.

High tunnels would be the next option and they are called high tunnels because typically, you can walk in them. They are also a good mid-level option since constructing a high tunnel can cost about $.50 per square foot as compared to $20 or more per sq. Foot of a greenhouse.

Here are some of the differences between a high tunnel and a greenhouse.

1) There are no temperature control systems in high tunnels. They rely on the sun to warm them up and summer breezes to cool them down.

2) High tunnel crops are usually grown in the ground or in raised beds, as compared to elevated tables and concrete floors in a greenhouse.

3) Greenhouses typically are attached to a solid foundation while high tunnels tend to have concrete anchors.

Galvanized steel or aluminum is typically used to build the high tunnel frame. This will provide a good, solid frame which is necessary to ensure your high tunnel will survive our Oklahoma winds.

Once your frame is built, you will want to cover it with a single layer of clear 6 mil polyethylene plastic. Typically, this plastic is attached in a way where it can be removed in the summer to prevent your making an oven which bakes your plants.

It’s also not a bad idea to have the floor of your high tunnel be a little higher than the surround ground to improve drainage.

As far as a location for your high tunnel, it should be located in a place that receives at least 6 hours of sunlight a day with the peak of the tunnel running north and south. Using your house or shrubs and trees as a windbreak isn’t a bad idea either.

In your high tunnel, you will be the thermostat. During the day, the sun will heat up your high tunnel with some of that heat being transferred to the soil underneath your tunnel. This heat will help keep your plants warmer in the night.

High tunnels won’t be a lot of help in very cold weather, but you can add a space heater if needed. Just be sure to have adequate ventilation.

Cooling the high tunnel on warmer days is typically accomplished by rolling up the sides or removing the end coverings to allow ventilation

Greenhouses are typically stand-alone structures but can be built in such a way as to use your house or garage as one of the walls. Essentially, you can spend about as much as you want to on a greenhouse with prices rising sharply if you add a heating or cooling system. Temperatures in greenhouses can be controlled by space heaters, a forced air heater, hot-water, or a steam system. Radiant heat lamps over the plants is also an option. Again, just be sure you have adequate ventilation for any system you plan on using to minimize carbon monoxide or ethylene accumulation.

In the summer, you will need to be able to cool the greenhouse down via windows or doors you can open, or you may need to install a cooling system. Yes, it’s easy to see why greenhouses can get expensive. The cost to operate an air conditioner as a way to keep your greenhouse cool is likely prohibitive, so some type of evaporative cooler would need to be installed.

Also, if you do construct a greenhouse, be sure your door is big enough to allow access for wheelbarrows or garden carts. It would be a shame to be all done with construction and then realize that you can’t get some of your tools inside.

For more information on greenhouses or high tunnels, visit the Hot Topics section of our website www.tulsamastergardeners.org. See you in the garden!

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org. Photo: Lynn Brandenberger