Producing Hydroponic Culinary Herbs

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There is no doubt about it — ornamental flowering crops are still the bread and butter for many greenhouse operations across the country. However, there are emerging opportunities for greenhouses to produce edible crops.

 

 

The increased interest in locally produced food is giving greenhouse growers cause to reflect on the products they grow. Are there opportunities to produce food crops in your greenhouse?

Switching over to tomato, cucumber or pepper production can be a big change for any greenhouse. These crops have long production cycles and may not fit as easily into windows of opportunity between ornamental production cycles. However, culinary herbs are a relatively quick and can easily be grown in simple hydroponic systems (Figure 1).

Select Your Crops

The first question to answer in hydroponic culinary herb production is, “What should I grow?” Herbs vary widely in popularity. Basil is, by far, the most popular culinary herb and is the most widely grown. Other popular annual herbs include parsley, dill and cilantro. Some popular perennial herbs include rosemary, mint, thyme and oregano. While you may want to focus strictly on the most popular herbs or those used in the biggest quantities, you still may want to consider growing some of the minor herbs such as sage, marjoram and chervil in order to offer your customers a complete suite of culinary herbs.

If you are looking to culinary herbs to fill an open space in an already-established production schedule, it may be best to focus on annual herbs. These crops are easily propagated by seed, generally require less time from sowing to harvest, regenerate quickly following harvest and do not grow extensive root systems, which make them more amenable to different production systems.
Alternatively, if you are looking at starting a longer-term herb program, perennials should be considered. Perennial herbs are commonly propagated from stem-tip cuttings, take slightly longer to reach a harvestable stage, regenerate following harvest and have a larger root mass, which must be taken into consideration when selecting production systems.

Choose A Production System

There are many ways culinary herbs may be produced. “Living herbs” can be produced just like containerized ornamentals grown in the greenhouse. A plastic container filled with a commercial substrate works well for this purpose. Managing nutrition for “living herbs” grown in peat-based substrate is also similar to fertilization strategies used for containerized ornamentals.
Alternatively, a hydroponic production system is a good choice for producing fresh-cut culinary herbs.

There are many hydroponic systems that would be amenable for culinary herb production — too many to cover in this article. The two systems that should be considered first are the nutrient film technique (NFT) and water or flow culture.

The NFT system is a relatively simple recirculating hydroponic system (Figure 2). The main components are a nutrient solution tank and troughs or channels that plants are grown in. The size of the nutrient solution tank will depend on the number of troughs that will be irrigated.

From the tank, nutrient solution is pumped up and delivered to troughs at the rate of around ¼ gallon per minute. The troughs range in size, but for annual herb production, troughs measuring around 2 inches deep and 4 inches wide are common; wider and deeper troughs may be used for plants with larger root systems, such as perennial herbs.

The length of the trough can also vary in length from just a few feet to up to 30 feet long. Nutrient solution flows down the trough, which are on a 1 to 3 percent slope, creating a thin flow or film (hence the name) of solution bathing plant roots. Additionally, the top of the troughs are usually covered to block out sun and impede algae growth. After reaching the end of the trough, the water is then collected and drained back into the nutrient solution tank.

One advantage of this system is that the constantly circulating water will usually have adequate dissolved oxygen in the nutrient solution — a key factor for hydroponic production. However, one of the drawbacks of using the NFT system is that if a pump fails and nutrient solution ceases to be provided to plants, problems may not be far off.

Another hydroponic system that is useful for herb production is called raceway, raft or floating culture (Figure 3). This system basically consists of a pool of water, ranging from 6 to 12 inches deep that is filled with nutrient solution. The pool or raceway can be constructed with a 2-by-12-inch board and a vinyl liner. Smaller, commercially built units may also be purchased. Polystyrene boards 1 ½ to 2 inches thick are floated on top of the nutrient solution and plants are placed in holes so that the root system comes in contact with the nutrient solution.

One challenge with this system is that without the circulating water, dissolved oxygen levels can decrease to sub-optimal levels and require aeration to maintain oxygen levels. However, one of the biggest benefits of this system is that plants are growing in the nutrient solution and are not dependent on pumps to provide water. In the case of a power outage, the crop will be fine until power is restored.

What Next?

This article is by no means a comprehensive guide to hydroponic culinary herb production. However, hopefully you now have a better understanding of the process and can evaluate if there may be a place for culinary herb production in your business.

I think that there is a real opportunity for culinary herb products. For example, let’s take a look at the holiday season. Fall and early winter (i.e. Thanksgiving through the New Year) is a time when people are getting together to celebrate with family and friends or with businesses and coworkers. This is a time when restaurants are busy and looking for locally sourced culinary herbs.

Alternatively, gatherings hosted at homes have appetizers or dinners as focal points and cooks will be looking for high-quality fresh herbs at their grocery store.

If you are looking for an alternative to poinsettias to fill your greenhouse in the fall and early winter before bedding plant production starts, hydroponic culinary herbs may be a crop to consider.

Christopher J. Currey (ccurrey@iastate.edu) is an assistant professor in the Department of Horticulture at Iowa State University.
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