Part 2 - Lettuce Blog

Optimizing Lettuce Growth with the Right Environment

We want to be able to produce a top quality crop of leafy greens economically, quickly and repeatedly. In Part One of the Lettuce Blog Series we discussed the Greenhouse Structures to provide the best possible space for growing, now let’s consider setting up the inputs to create the best possible growing environment in that greenhouse.

The first consideration is water.
For hydroponic growing it is the medium that the plants live in and that supplies the plants with the nutrients they need. The first thing to always do is have your water source tested so you know exactly what its analysis is. Don’t forget that some sources will vary at different times of the year. In most cases pretreatment of the water is minor and can consist of as little as adding some acid to bring it into a comfortable level. When setting up the system GGS can recommend the best solutions for your specific needs.

Deep Water Culture Lettuce

In both NFT and Deep Water systems the water is constantly flowing. It runs through the beds or troughs and is recycled. The flow may be different for various systems but the basics are the same. As the water flows back to the storage tanks it is tested for fertilizer levels. It is also filtered and additional water and fertilizer are added as needed. Then it is ready to be recycled. In some cases the water temperature can be adjusted, more often cooled during hot summer days to help prevent plant stress. Oxygen levels are another consideration. Along with our hydroponic system partners, GGS has all the automated system solutions for your fertigation/irrigation requirements.

Light matters.
Level of light, type of light and duration of light are significant factors in quality and growing time needed for leafy green crops. There is an extensive amount of ongoing research for the effects of light on plant growth, crop timing and quality. The growing time of most leafy greens can be reduced by as much as 20%+ by adding extended day light. Starting when the seedlings are put into the greenhouse on day 2 the light levels are increased and the length of day extended. Depending on the intensity of the light levels growers will extend the day to 16 up to 24 hours. Most of the growers seem to run 17-18 hours per day. As much as leafy greens like the light, on intense summer days you may need to close the shade curtain from about 9 to 4 to avoid intense light and the high temperatures that can be generated. These factors can cause tip burn. Also adding calcium to the fertilizer and turning on some of the circulation fans to add vertical air flow will help.

This brings us to the discussion on the lights. Do we go with HPS or LED? Traditionally HPS were the greenhouse standard. They still are very popular because they are proven to work well and their cost is about a quarter of the cost of an LED. LEDs are no doubt the future of lighting and the amount of research and advancements we have see in their technology over the last few years is amazing. With that being said you have to be careful. The number of companies in the LED light business has exploded. With that the pricing is all over the board and the claims of what each suppliers’ lights will do makes it hard to decide the best one. At GGS we are constantly monitoring the advancements and checking to make sure there is credible testing in greenhouse plant production backing up any claims. You do not want to find yourself with a light that was better suited for a parking garage than growing plants.

Specifically for leafy greens light spacing is 60-80 sq. ft. per light. There is some disagreement as to what to choose. In the colder times of the year, HPS gives off some helpful heat. In the south LEDs may be the better choice because they are cooler. There are also electricity savings with LED lights. The latest research shows that in the last 5-7 days before harvest if you give the plant blue/red light especially for red varieties of leafy greens your get a stronger more intensely colored plant. With all the advancements and research into best growing practices lighting will be a major talking point for optimum production advantages for quite a while. Consult with GGS specialists for lighting solutions designed for your specific production and budget requirements.

Keep it Cool.
Cool pads placed over the vents are the standard solution for keeping the greenhouse from getting too hot for summer production. Water is run through the pads and as the exhaust fans draw the air through the vents and through the pads the air is cooled. It should be noted that greenhouse grown leafy greens do like a cool climate. We have been in greenhouses in the heat of the summer that have beautiful crops. Cool pads are a standard solution. You can also cool the water in the troughs or ponds. A relatively new option for cooling is high pressure mist systems to reduce temperature. As mentioned earlier closing the shade/energy curtains during the hottest part of the day also helps prevent stressing of the crop.

But not Too Cool.
The heating plans for a leafy greens facility vary. For Deep water culture in southern climates as little as a forced air heater to supplement is enough. The large pools of water moderating the greenhouse temperature is a factor in planning the right heating system. Where seasonal temperatures are colder a Hydronic heating system than can include boilers, headers, mixing groups, main distribution and return lines, overhead heating, under bench heating, snow pipes, perimeter heating etc. are recommended.

For an NFT growing system the Hydronic heating system is recommended because you will want to put hot water loops under your benches for bottom heat. Niagrow, a part of the GGS Group of Companies specializes in heating system. They design heating systems to create ideal growing environments for all plants. Contact our GGS team on this and more to help you with your growing business.

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