Structures & Equipment
The Sky’s the Limit with Vertical Farming
By Dr. Mohyuddin Mirza
By Dr. Mohyuddin Mirza
DECEMBER 2016 – Cold climate, economic downturn, empty buildings and warehouses have always spurred interest in indoor horticulture. Various terms have been used, such as indoor farming, vertical farming, container growing, vertical walls, and many others.
My memories took me back to 1985 when I got involved with a warehouse farming project in Spruce Grove, Alberta. A computer engineer there had become fascinated with using technologies he had developed and he had learned to grow plants on a hydroponics system. He built a smaller unit inside a building, installed a few high-pressure sodium (HPS) lamps and started experimenting with growing lettuce. The goal was to grow butterhead lettuce of a size comparable to what was being imported from the U.S.
EXPERIMENTING AND RESEARCH
Considerable time was spent in experimenting and research. Resolving tip burn issues, root tip death, nutritional deficiencies and some time toxicities were just a few of the challenges. I remember changing the nutrient program and we did produce some excellent crops … and some not-so-good crops.
Finally, a very impressive indoor farm was built in a large warehouse. Included were five levels, sections of eavestroughs that stretched from the planting end to the harvest end, robots for transplanting lettuce, a water recycling system, and good packing equipment.
The focus was on growing and marketing butterhead lettuce in the range of at least 250 to 300 grams. The biggest cost was in maintaining the proper temperature for lettuce.
In a year’s time this facility was out of business and the reason was the market. Wholesalers would not pay more than what they were paying for lettuce from the U.S., although the quality was good, and it was locally produced with no pesticides applied.
Today there is considerable interest in building and operating vertical farms and there are many different types of vertical farming systems that have been built or are being built. There are claims of proprietary technologies and design patents. Here are few examples of projects in which I have had some role in their development.
- Photo A: This is an A Frame vertical growing system using PVC pipes with holes. Plants are inserted into two-inch diameter pipes containing a growing medium. Water and nutrients are supplied from the side (black pipes) and drained on the other side into a tank. The pH and EC are adjusted and the nutrient solution is recycled.
- Photo B: A crop of Swiss chard and other leafy greens. Sunlight is the only source of light. There is no separate temperature control system. Reasonably good crops are being grown by some growers. Tip burn is still an issue with some lettuce varieties.
- Photo C: A grower built this learning model inside a greenhouse to grow leafy greens with LED lights. It featured four layers. This was his prototype for aquaculture.
- Photo D: This room has been fitted with lights and fans for air circulation for growing microgreens.
- Photo E: LED lights can be utilized.
You can also use a vertical unit of several layers in a warehouse. Building simple vertical units, looking much like shoe racks inside a greenhouse, is a popular concept. You can easily buy them, stack them, put trays in and start growing.
MAXIMIZING SPACE USAGE
I have also seen plants grown in a vertical setup. Here, pipes or troughs are placed on walls and plants are grown in holes. Basically, the idea is to use the maximum amount of space. How you provide light will vary based on the setup. What knowledge is essential to make these ventures successful?
In my opinion growers or would-be growers may try to fit the plants into a manufacturing type of warehouse. They may forget that plants have their own business and if that business is not conducted properly and optimally, then forget about your own business.
Before talking about essential plant parameters, check with the bylaws, development permits and building permit requirements. A grower has to spend several thousands of dollars to get drawings made for the structure, plumbing, water use, etc.
In many vertical farms, the grow structures are built inside a warehouse and there is no sunlight available. At best, sunlight may be made available by installing windows at the roof and some light may come in for the top layer.
The biggest challenge for growers is to select a suitable source of light. The preference for many of them is to go for LED lights. I know of two would-be growers who experimented with different types of LED lights at different heights and actually grew plants and recorded their weights, etc. The light distribution, however, was so erratic across the growing surface that there were growth problems. The information from different companies was also difficult to bring to the same level to make good comparisons.
It is not only the light in micro-moles/sq/m/second but the proper spectrum is also needed. Due diligence is required in selecting lights. Also if you select LED blue and red spectrum lights, then also include some white bulbs for the human eye. The lighting should be comfortable for employees.
It’s important to understand the term “PAR.” Photosynthetically Active Radiation covers the range from 400 to 700 nanometers. Know the language of light when you are talking to suppliers of lights.
Beside PAR, it’s important to also understand the term PBAR – Photobiologically Active Radiation. This includes the UV range from 280 to 400 nanometers and provides some critical information for plants.
Also learn about “kelvin,” the Color Rendering Index, and watts/micromole.
So my suggestion is to ask lots of questions when talking with representatives of LED manufacturing companies and also prepare for your light distribution in the units you are planning.
For example, if typical beds are four feet by eight feet (32 square feet) and lights are to be installed 12 inches above the beds, then ask how the light will be distributed. Once plants start growing they will reach closer to the light and the top leaves will get much more light. I have seen lower leaves turning yellow on basil, arugula and kale due to poor light. This means you may have to harvest the crops earlier.
I have seen some LED light spreadsheets on 32 sq./ft. production trays ranging from 140 to 280 micromoles/sq.m/second. Under such light spread expect to see plant growth variations.
I see a big challenge in providing proper climate control inside a warehouse for multiple crops. When we talk about climate, we mean temperature, relative humidity and carbon dioxide.
Air conditioning the entire warehouse is one option but it would be expensive. Cooling the warehouse when lights are on will be required.
You then have to decide how dehumidification is going to be accomplished. I have seen problems where air conditioning units are being used for dehumidification as well. These problems are related to leaf edge burning, leaf tip burn, edema and water condensation inside of young heads of lettuce.
Some growers have suggested covering each unit with some plastic material but then how is the air going to be moved?
Just be aware that if root temperature is higher than leaf temperature, then many of the previously listed problems can develop.
I will write on water and nutrient management, diseases and insect control strategies and some other aspects of vertical farming in an upcoming issue. There will be a learning phase to make vertical farming successful.
Dr. Mohyuddin Mirza is a greenhouse consultant. He can be contacted at firstname.lastname@example.org.