From pansies to peppers

It is becoming more common for me to walk into greenhouses and see changes afoot in production. I am not referring to new genetics or cultivars of flowering ornamental plants; I am talking about entire greenhouses transitioning “from flowers to food.” There is no denying that production of food crops in greenhouses is on the rise. While there are new facilities dedicated to food crop production being constructed, there are many greenhouses that are transitioning anywhere from some to all of their production from ornamental flowering crops to food crops.

There are a number of factors contributing to the increasing number of growers starting to produce food crops. Some of the reasons include: an increasing demand for fresh, local foods by consumers; a reliable and consistent source of produce for grocers and restauranteurs; and, the ability to grow a very high-quality indoor crop in the off-season that has more value than its field-grown, shipped-in counterparts. And we can’t overlook the opportunity for increased and even new revenue streams.

Whatever your reason(s), if you are contemplating making the transition from flowering crops to food crops, there are a number of points to keep in mind before switching that will help your transition. This article aims to highlight some of the most important considerations you will need to make when initiating a transition into greenhouse food crop production.

What is your market?

How are you currently selling your products? Are you a wholesaler? A retailer? Wholesalers have the advantage of being able to specialize production for a narrower product mix. The efficiencies that come with growing few crops can really pay, especially in large-scale facilities. Alternatively, if you are retailing, you’ll likely want to carry a more diverse product mix for your customers. There are a few different ways you could approach this. You could try to grow a wide variety, from leafy to vining crops, though trying to grow a wide variety of crops in similar conditions can pose some challenges. Alternatively, you could specialize in one or two crops and purchase other types of produce from other growers to retail alongside your crops.

What are your crops?

Once you have decided to grow food crops, you have to identify which crop(s) you will be producing. There are numerous crops that can be grown successfully in greenhouses, and I tend to lump these crops into one of three categories: 1) vining crops; 2) leafy crops; and 3) small fruits.

Vining crops include tomatoes, cucumbers, peppers, eggplants and melons. One characteristic of these crops is the longer crop cycles ranging from 3 to 4 months to up to a year; they are not suited for quick turns or short-term greenhouse production. Additionally, these vining crops require regular plant maintenance such as trellising, pruning and training. Hydroponic systems such as rockwool or coconut slabs and Dutch or BATO buckets are most frequently utilized for producing these crops.

Leafy crops, including lettuce, greens and herbs, are a bit of a contrast to the vining crops, with respect to their attributes. Leafy crops generally have a short crop cycle, as short as five or six weeks from seeding to harvest, making them well-suited for short-term production. Additionally, leafy greens and culinary herbs are most frequently produced in nutrient film (NFT) or deep-flow technique (DFT) hydroponic systems. There is no plant maintenance such as pruning, training or trellising; once the seedlings are planted into systems, they do not need to be handled until harvest unless you are performing multiple harvests on culinary herbs.

Small fruits such as strawberries and brambles are not nearly as widely grown as vining and leafy crops, but they are produced using systems that generally utilize a soilless substrate. While these more challenging crops are not widely grown, these crops have the potential to produce a premium products and profit.

Where are your knowledge gaps in production?

Once you begin looking at how to produce your crop(s) of choice, identify which aspects of production you will need to start brushing up on or learning about to try and ease the transition. When I compare floriculture and food crop production in greenhouses, there are clearly aspects where production is similar, though there are also several ways where production can be quite different.

Most greenhouse growers transitioning into food crop production have experience growing crops in substrate in containers. This knowledge of substrate, including the physical and chemical properties of growing substrate and how to manage irrigation, can be useful if you are transitioning into production systems that utilize substrate more than others (Fig. 1). For example, producers growing culinary herbs in containers or strawberries being grown in hanging baskets can utilize their experience with substrate in when managing these crops. The bigger learning curve comes with systems utilizing a smaller volume of substrate relative to the size of crops, such as slabs of rockwool or coconut coir for tomato (Fig. 2) and cucumber production or, even more, with water-based systems such as nutrient-film (NFT; Fig. 3) and deep-flow techniques (DFT).

Are you currently capturing your irrigation runoff and recycling it for use in production? If so, you are already working with a type of recirculating water culture. One of the biggest benefits that hydroponic production systems can offer is the ability to recycle nutrient solutions. For systems such as NFT and DFT, this recirculating culture is inherent in the design of the system. For production in Dutch/BATO buckets or coconut or rockwool slabs, these systems can be open (drain to waste) or closed (capture and recycled). Recycling water for hydroponic food crops is similar to ornamental crops, though more intensively managed. The irrigation water or nutrient solution must be adjusted to the appropriate pH and have the appropriate amounts and ratios of mineral nutrients, as well as being sanitary.

Just like floriculture crop production, light has a large impact on crop quality and yield. When the three different aspects of light are considered — quantity (daily light integral and light intensity), quality (spectrum or color) and duration (photoperiod) — light quantity has the greatest impact on food crop production in greenhouses and controlled environments. This can be attributed to the fact that finished food crops are sold based on weight and increasing the quantity of light (including light intensity and daily light integral) increases photosynthesis which, in turn, increases growth and mass. Unlike many floriculture crops, the photoperiod, or duration of light, is not very important for production, even for crops that require flowering such as the fruiting vine crops. One exception to this rule is strawberries; depending on the type of cultivar you are growing, photoperiodic lighting may be required.

Similarly, the principles of managing temperature are similar for ornamental and food crops. Managing the average daily temperature can help make yields and harvest more predictable, similarly to how it is used to control time to flower for ornamental crops, whether it is a tomato or a basil shoot. Like floriculture crops, excessively warm temperatures can cause flower abortion. Instead of reducing value from delayed flowering and diminished ornamental appeal, fewer flowers reduce yields of fruiting vegetables such as tomatoes and peppers.

What next?

Producing floriculture and edible crops may seem as similar as apples and oranges (or, more appropriately, pansies and peppers). But the transition can be made more smoothly with the proper planning and preparation. Carefully assess where are you are, where you want to be and what it is going to take to make those changes.

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