by William and Mary Weaver
Consider growing hydroponic herbs and greens in your greenhouse this fall, in place of traditional fall crops with “commodity” prices. Greens and herbs grown in a fall greenhouse have several advantages, according to Dr. Chris Currey, of Iowa State University.
First, herbs can be sold value-added simply by packing them in clamshells and selling them in the produce section of a grocery store. Second, you can often produce greens and herbs without using pesticides. Third, your product will be superior to field-grown because it can be grown clean hydroponically in the greenhouse.
Finally, after your final harvest, you can take out your hydroponic set-up rather easily without having to retrofit everything to return to growing your usual spring bedding plants.
Currey recommends growing a wide variety of herbs — specializing in basil and parsley, and three types of lettuce: butterhead, loose leaf and romaine lettuce, “which also works well in this system, but is not as widely grown.”
In herbs, said Currey, “Your mainstays will be basil and parsley, but it will be important for your marketing that you also devote some space to more minor herbs. If you hope to sell your basil and parsley wholesale or to restaurants, you’ll be more likely to succeed if you can supply their need for all the herbs.
Choose your varieties carefully, Currey advises. “Our challenge is that most breeding is focused on field crops. There’s not a lot of breeding being done specifically for hydroponic greens and herbs, as there has been for tomatoes, cucumbers and peppers.”
It really pays to do your homework on varieties; you have the opportunity to choose the genetics of the variety you plant. Talk to seed companies and other hydroponic growers. Email your State Extension specialist. “One of the best ways to find the best hydroponic varieties,” Currey continued, “is to conduct your own variety trials, although taking the greenhouse space to do this could put the squeeze on your square footage.”
Currey mentioned several potential problems to avoid by your choice of varieties. Taller basils can tend to “lodge,” in a hydroponic system and can desiccate. To avoid this, choose the shorter basil varieties.
Also, with basil, take into consideration the leaf size. “The larger leaves are actually preferred by chefs. They take less time to chop, and can be used in specialty dishes, like basil wraps.”
Also, be aware that depending on the basil cultivar you choose, you can get a three-fold increase in mass from variety choice alone, without changing anything else. “The variety ‘Genovese,’ for example, will yield about 17 grams per plant. Choose a better yielding variety instead, and you can triple the weight of your harvest.
Consider also how much branching you want in your basil variety. Large leaf basil grows six branches, which can increase the amount of time you’ll wait until it regrows for a second harvest. The variety “Emily,” on the other hand, branches very little.
Currey, however, does not recommend trying for multiple harvests from the same herb plants. “I fundamentally support a single harvest program for the sanitation of the greenhouse,” he explained. “We don’t have a lot of pesticides labeled for herbs, and besides, spraying for disease runs counter to the pesticide-free image that customers like. Save yourself a lot of headaches and produce a nicer product by replacing your plants after each harvest. You can be planting and harvesting herbs at all stages, saving labor.”
For producing seedlings for hydroponic systems, you don’t need specialized facilities.
Germination is simple using a bench with heat mats. Like herb seed, lettuce seed is not pricey unless you buy pelleted seed or a high-priced variety like ‘Rex’ buttercrunch.’
“We use 164 or 276-cell trays. The 276 is the smallest I’m aware of. With the bigger cubes you can wait longer to transplant, but we generally transplant after two weeks. I use phenolic foam (Oasis) rather than rockwool or netted peat blocks. Oasis dries down more quickly, giving me the opportunity to water again, rather than staying wet and waterlogged. Oxygen in the root zone is important.”
Use of the Nutrient Film Technique for your hydroponic system has the advantage of placing the plants at a comfortable height. The nutrient solution is automatically oxygenated as it moves through the system, frequently using troughs on a slope, with spaghetti tubes delivering water to bathe the roots in a relatively thin nutrient solution. This system is vulnerable if a tube becomes clogged, or the pumps stop during a loss of power, since there is so little water in the system to begin with.
You can also use a Floating Raft System, which has the advantage of high density planting, eliminating aisles. The ‘rafts’ have holes drilled at your chosen plant spacing. This system has other advantages over the Nutrient Film Technique. Since the water is deep, power outages are not a serious problem and there’s no worry about clogged spaghetti tubes.
The floating raft technique requires oxygenation or aeration of the solution, since the roots are submerged. But if the pump goes down, it can be awhile before roots suffer from lack of oxygen. Depending on the time of year, you may need to chill or warm the nutrient solution. Designed properly, floating raft systems can have labor savings.
For recirculating hydroponic systems, start with the best water you can access, such as well, municipal, or re-ionized water to extend the life of your nutrient solution.
“Growing cool,” for herbs and greens, can slow production of new leaves, delay harvest, and actually increase production costs. Into the 70’s is a desirable growing temperature for most herbs, and also works well for lettuce.
Consider hydroponic herbs and greens for your fall greenhouse
by William and Mary Weaver