Lettuce production thoughts.

[jamromhem]

I was thinking that lettuce production could be made a "mass production" system relatively easy with 3 systems. I wanted to run my thoughts through here and see what people think.

First system is the seed starting system. It will be a virtical stack of rails each with an NFT/spray system. (similar to the one I have on my first system) The rows will only be about 6 inches apart from eachother (virtical spacing) to let you put a large number of rows on top of eachother. The water will be able to get more airation through the splashing of the spray. And you can have a single Flouresent fixture on a hing to fold down to provide light to young seedlings. and you can get small plastic trays from your local garden shop to serve as humidity domes over each plant.

Second system would be similar. Probably slightly higher spacing virtically. The lights can be mounted just below the rail above, or still be able to hing towards the rear of the unit to allow more functional space when moving plants in and out. This system would be running the light strength nutrients, and would be for the mid ranged plants.

The third system would be the production system. This is where the mature plants will be and could have a few different designs... I would think an angled rail would be more space efficient with the roots being developed by this point. You could have this one with natural or supplimental lighting as needed.

This wouldnt take much room and could probably be downsized to a few 2ft wall spaces (with 2ft flourescent lights) with ease, and would let you produce much more lettuce than a single family could eat in most cases :P

This is just a thought. Let me know what you think and I might make a set for the personal entertainment value :P

[GpsFrontier]

How many lettuce heads are you wanting to harvest weekly? Are you wanting to grow more than one variety? If so, what types, and how many do you want to harvest of each weekly? When you say "mass production," are you thinking of a commercial grow operation to sell the lettuce?

[jamromhem]

I was figuring I could harvest as many lettuce as I can grow with my power/space constraints. More of a test bed for expanding later. The more I can grow in the smallest space with the least energy, the more I can plant for when I get some land. I will probably be wanting to do some commercial growing for the local area later for some side income/to keep me busy.

[GpsFrontier]

The reason I asked was basically because the amount of plants, as well as plant needs would dictate the best type of system. But overall for a continued supply of lettuce heads, 3 separate grow stages in rotation is a good plan (seed propagation, seedlings, then maturing plants). However the NFT/spray system will become complicated and more expensive on a large (especially commercial) scale. As well as the spraying will become unnecessary with the 3 growing stages because the roots will grow long enough in the second stage. The two most common methods to grow lettuce commercially are either NFT, or Water Culture systems. Weather the system you use for the maturing lettuce plants (any variety) is an NFT, or Water Culture, I would build the the propagation and seedling setups the same.

The proprigation
Propagation trays you can get at most hydroponic shops and cost only a couple of dollars. They generally hold about 72 sprouts (cells) in each (10x20) tray. Two twin 2 foot florescent lights (T5, or T8), would be sufficient for up to two 72 cell propagation trays for lighting (less light would probably result in elongation). Or two 4 foot twin lights for up to five 72 cell trays. Depending on location and time of year, you may need to use artificial heating or cooling to keep the air temperatures in range.

The seedling setup
Each sprout would now be transferred/transplanted into the basket/cup they will mature in to keep labor to a minimum, as well as allow the roots to grow through the baskets/cups (making it imposable to transplant them again without root damage). Smaller heads like butter lettuce, or grand rapids leaf can probably do fine in 2 inch cups, while large heads like romaine lettuce will probably take 4 inch cups.

The easiest, simplest, cheapest, as well as most space productive seedling setup I can think of is a water culture system. How large depends on how many plants you will be growing. For a commercial setup, a custom built system would be the cheapest as well as most productive. But for a home system, modifying short plastic storage totes with a lid would be the cheapest, as well as simplest (about $8 ea at wal-mart). Using storage totes like the ones I've used in the past. (picture attached). Light proofing the base by painting it black, then white to reflect light. Then cutting holes in the lid spaced closely together (like the attached pictures). They wont be in the system long enough to become crowded.

The main system for maturing plants
The easiest main system could be either a Water Culture, or NFT system. Depending on how many plants will be growing in it either would be very productive. Fallowing the same design setup as the seedling setup, and expanding it to multiple growing chambers as needed is relatively simple. Just spacing out the holes for the lettuce plants farther apart to accommodate the full grown plant. Like to 8 spots per container like I did with my lettuce. However if a large number of plants is planed, or large verity like romaine lettuce are planed. A costume built system would be more cost effective, as well as productive. But again NFT systems are very productive for growing lettuce, although the 4 inch square fence post tubing is very expensive for such a setup. But again large varieties like romaine would benefit from the oversized tubing because of their size. Though small varieties could just as easily use rain gutter downspout tubing instead.

Plant Rotation
Deciding on how many plants you want to harvest weekly will tell you how large of a system/s you'll want/need to rotate production. As an example if you wanted to harvest 1 lettuce head every day. That would be 7 a week. Generally lettuce plants (most smaller varieties) take about 6 weeks to go from seedling to harvest. So 7x6=42, then add another week for the seeds to germinate (7 more plants)=49. So in that case you would want a minimum of 49 total plants going at any given time to ensure the harvest quota of 1 lettuce head harvested every day. Also each week starting a new batch of at least 7 new sprouts (probably a few extra in case some don't germinate).

So depending on your growing conditions (a large factor in how fast they grow). Sprouts would be ready to put into the 'seedling system" about a week after germination, where they would remain for about 3-4 weeks. From there they would be large enough to go into the main maturing system for another 2 to 3 weeks. So I would expect it to go something like this;

14 to 28 germinating sprouts at any given time (first 2-3 weeks)
21 to 28 plants in the seedling system at any given time (next 3 to 4 weeks)
14 to 21 plants in the main plant maturing system at any given time (last 2 to 3 weeks)

Total growing time "once seeds germinate" between 6 and 9 weeks. Then taking these numbers I would design and build the system/s to accommodate at least that amount of plants. Then I would also know what I could realistically expect in the way of harvest, as well as cost to build, space needed etc.. Even energy consumption once I knew the amount of lights I needed, air pump/s, water pump (if the maturing system was a NFT). By gathering the total wattage for each electrical device, and figuring the amount of hours each will be used. Then imputing that data, as well as what I pay per kilowatt hr (found on your electric bill) into a Electricity Cost Calculator.

[jamromhem]

Thank you for the Very impressive and thought out post. It gives me a good bit to think about and work on for my system. You make a lot of very good points, and I will probably use a lot of your ideas.

I will let you know what I come up with. I will be rethinking a few things in my system. and finding some more information about what I am using I will be able to manage my grow medium a lot better, and cheaper.

[Paul Perkins]

First, thank you very much for your thoughtful and informative posts in this thread. As suggested, I went to WalMart and bought 4 of their 10 gallon blue Rubbermaid Roughneck totes with lids ($8 each) and drilled six 1-7/8" holes in each lid to accommodate 6 of my 2" netpots with lettuce seedlings that I had already started in rockwool a few weeks ago. Also as suggested, I added an airstone connected to an air pump, added my water and nutes and can't wait to see (and taste) the results. However, this experiment raises a few questions:

1. Do you have any suggestion as to how high the water level should be inside the totes? Up to the top? Just above the bottom of the netpot? Does it matter so much as long as the roots are wet and the water is aerated?

2. Re: the seedling stage. After germination, I read that you suggest a storage tote with more holes spaced more densely together for growth prior to moving into the main system. Other than the closer spacing of the holes, do you do anything different in the "seedling" stage than what you do in the "main" stage? For example, I've also read that the nute solution for seedlings should be 1/2 strength versus growth stage. True? Do you give your seedlings more sun/less sun? Lower waterline of the nute solution to just wick the rockwool versus immersion, etc.?

3. In your pictures, I see you built a shade over your lettuce. I live in Central Florida where our afternoon sun is nearly comparable to the intensity in AZ. Did you find that without shade your lettuce couldn't handle the intensity?

4. What propagation medium would you suggest for lettuce?

5. Finally, for a custom DWC lettuce growing setup, what do you think about using a Firestone PondGard EPDM "Fish Safe" liner inside a wood frame with blue foam polystyrene as a float surface? Any suggestions on how deep a DWC system should be? Is EPDM safe? Any better materials to use?

Thank you for any suggestions or experience you can offer.