Thanks. I hadn't thought of the toggles, but those are ideal. I finally found someone who had taken temperature readings and made observations doing Kratky in very hot environments, and he found that high temperature, even high water temperature made little apparent difference. His theory is that the plant can do some of its own cooling bu evaporation.

Cool weather, which I will end up dealing with for our brief winter will surely slow plants down, but mostly the area I have warms up nicely during the day. I'll see how it goes. I can stand some slow-down.

I found some 17-quart black storage boxes at a not too high price, and I may pick up some 5-gallon buckets. My Tractor Supply sells their logo'd bucket with lid in opaque red very cheaply. But they might cramp the vertical space on shelves when plants begin to get taller. But I already have jars, so I may start there, too.

I happen to have a nice aluminum rolling rack with three shelves and an open bottom space, about four feet wide, which fits with the grow lights, which are about four-foot sticks, six of them. I also fell into a new (QA reject for a bad LED) set of three pairs of 48-inch 150W per pair professional LED grow light strips, ballasted in pairs, so they're convenient to mount two under each of three shelves. That's about 40W per square foot of available shelf area, which seems to be the recommendation. Wouldn't want to have to buy them new, after looking at prices.

Thanks. I'll report back with photos as I go.

First, just let me say I encourage everyone to do their own experimentation and trial/error. But I will offer up a couple of thoughts. I read somewhere that each head of lettuce will require more than a gallon of water over it's life. As I said in an earlier post, when I used smaller containers, including a 32 ounce pickle jar, I had to refill the solution lots of times. And once you are refilling, you can only fill the jar about 1/3 the way so you don't drown the roots. Refilling got to be a regular activity. And those plants did not get very large. I just think the jar was too small for proper root growth. With a single jar, refilling can be difficult because you have to lift the net cup out to access the inside. I broke off many lettuce heads accidentally doing this. It's awkward and cumbersome.

When I did my larger containers with 4 heads per box, I started with somewhere between 3.5 to 4 gallons of solution for 4 lettuce plants. I still have to refill those too. The dimensions on these boxes are around 16" long, 11" wide, 7" deep. The water lasts long enough to get the plant to maturity, and then maybe a couple of weeks more. So maybe like 6 weeks total, then start refilling. Sorry I didn't pay better attention on that. I am getting ready to start a new box soon, and will document better. And I will try to upload some pictures of the setup process I do with the pool noodles.

Anyway, the biggest part of the fun in all of this is experimenting and trying different ideas. I have my system nailed down well with lettuce so I can keep regular production going continuously. But I am still experimenting with other plants and containers too. So, whatever you do, just enjoy the process and see what works for you!

Oh, one more thought. I have done all of my lettuce indoors, in a closet under lights. There is zero ambient light or sunshine from outside the closet. I turn the lights on in the morning and off at night. Probably around 14-16 hours per day of light. The temperature in the house remains steady between 69 - 72 F. However the closet gets to 80+ degrees (because of the lights) if I don't leave the door open and have a little fan blowing in to passively circulate the air. Lettuce begins to bolt (make seeds, leaves turn bitter) at around 80 degrees. So it's important to monitor your room temp if you have lights that put off heat. My greatest success has been with Paris island cos romaine and giant Caesar. Black seed Simpson grew well, but I just don't like it as much. Every time I tried Bibb lettuce it started bolting immediately once the plant reached maturity. I do "cut and come again" harvesting, so the mature plant needs to live in a while. My current plants are just at 2 months old. 1 month of growing to maturity, and one month of harvesting every few days. I am about to toss them and start a new batch.

On the solution and containers... they get really nasty by the end of a plant's life. I dump whatever is left and wash the tub with bleach. I also wash my other parts with bleach (cups, pool noodle, rocks etc).

Well, I will definitely go with slow-to-bolt varieties. My location will be on that mostly enclosed porch where it is only modestly cooler than the exterior, meaning it will very warm indeed in high summer. I can't do much about it, since there is no workable temperature controlled area. But I see people growing successfully in hot weather, so we will see. I also will have considerable ambient light. no direct sun, but a glass wall facing a shaded area. So I'll match the lights essentially to the natural cycle as much as possible.

I do see some examples of tomatoes and squash and such doing very well outside with water temperature hitting nearly 100F. Tomatoes and all set just fine. Perhaps the steady availability of water lets the plant regulate its temperature by evaporation. I'll have to find a very small temperature probe to test that idea. One way or another, I'm doomed to become an authority on hot environment Kratky. The thermodynamics among the water mass, the water surface, the gas area above the water and in the plant tissues has to be complex, so the usual temperature rules for gardening may not apply so strictly.

Your experience with constant refilling follows my experience with large self-watering outdoor planters where you can actually tell how much water the plants and soil are demanding. And it's far more than one would guess.

I'm inclined now to begin with 5-gallon buckets, which I can get fairly cheap and in opaque color and can take one to five plants each. General storage boxes seem too flimsy for the water load. And the buckets are better suited for placing outside in useful weather. And five gallons may be enough water mass to slow warm up from overnight temperatures, if shielded from daytime radiant heat. I will probably start seeds indoors under lights at all times and move outdoors where workable. I have a rack that is easy to reconfigure for shelf height.

I also don't see examples of plants in 32 ounce jars reaching their full size potential. Seems to work okay with culinary herbs that don't get so large anyway, and I'll probably do some that way.

I want to make this work in all seasons for the fresh greens year round. And I really want to push the normal envelope on tomatoes.

You brought an interesting question to my mind. I don't know if the heat-sensitive nature of a lettuce plant is in the leaves and outdoor temp, or if it's the roots and soil/water temperature. Maybe it's both.

Now, as far as tomatoes go, I have had great success with Kratky tomatoes both indoors under lights and outdoors. I'm in south/central Texas, like you appear to be, and it gets hot inside my outdoor Kratky containers. But the tomato plants are doing fine and producing a lot of fruit. They are the "husky cherry" variety.
My indoor tomato is about 3.5 feet tall, and has about 25 tomatoes in various stages of growth. And it appears to be putting up new stems and leaves all the time, and has lots of blooms still developing. The ones outdoors were set up in the Kratky containers at the same time and of course grew much faster than the indoor plant. But it looks like the indoor plant, while growing slowly, will thrive and produce lots of tomatoes for me. They are indeterminate, so I don't know how long the indoor plant will last. No weather or temperature change in the fall or winter, so will be interesting to see how long it goes.

I'm actually pretty excited about my indoor tomato plant. Never thought it would work, but figured I would try just for fun. I doubt a plant that produces larger "slicing tomatoes" would work inside. But still may try it sometime.

The indoor plant, compared to the outdoor plants, is incredibly clean and dark rich green, and absolutely no sign of pest or disease.

Definitely choose some heat tolerant lettuce varieties, and I'm sure you will do fine. Might also consider ways to shade the container from the sun. I have put old window screens against my outdoor container to block some sun. Helps keep the box a little cooler.

I will be anxious to hear how your setup goes! Keep us updated.

https://youtu.be/4FBfIqFIj3c

I hope that link works. I do my "pool noodle method" similar to what this guy does in his video. But I don't use hemp mat. Just use a little extra piece of pool noodle to gently wedge in the center hole, just barely tight enough to keep the seedling suspended above the water.

https://youtu.be/JXKfIASdSqM

Another good video on the subject

I started my 2nd set of 3 jars on Sunday. One thing that amazes me is how fast you begin to see growth. In less than 48 hours, the small white fuzzy root begins to emerge, and in less than 72 hours the first two green leaves can be seen. Nature is truly a wonder.

Good to know about having to refill the jars. I will keep an eye on that.

The pictures below are of one jar planted with 4 seeds of Paris White Romaine 11 days ago. While they are still small, you can see the root structure is developing well, and the water level is down about 3/4 of an inch to where I filled it before I put the net cup in on Day 1. Not hard to imagine the water being used quickly.







I imagine each one of these plants will get quite large. Of these first 3 jars, I am going to thin 1 jar to 1 plant, the 2nd jar to 2 plants, and the 3rd jar to 3 plants, and compare them as they mature.

I think I am going to start some spinach seeds, although I have been told they don't do as well using clay pellets. Someone told me to use vermiculite and peat (I think that's what they told me.)

Murphy, seen this one. Shows water and container wall temps outdoors.

https://youtu.be/OcpFULoPfEo

And yes, I'm south Central Texas. Heat index only 105 today.

Yes, Jim, you are absolutely right. It really is amazing how fast things grow in hydroponics. I don't know the full dynamic, but I assume it has something to do with us setting up the "perfect" and "least resistive" growing environment possible. The roots are growing freely through water, so there is no energy being spent for the roots to fight their way through packed soil. The nutrient solution (theoretically) provides a perfect balance of "food" the plants need, and there is abundant water continuously available. And when done indoors under lights, the cycles of light and dark are perfectly balanced, and there are no cycle interruptions by cloudy days or changing weather. The plant spends no energy "adapting" to an ever-changing outside environment and weather and temperature. Everything remains in a (sort of) perfect balance, where the plant may spend all energy available to grow healthy roots and healthy leaves, and it's never deprived of anything it needs. All variables are controlled.
I have not really researched any of this, but that is my working hypothesis on the matter.
But, yes, it makes for rapid growth, which is certainly fun to watch. And you can do it year-round without worrying about the changing seasons.
Of course my indoor tomato plant didn't grow super fast like the lettuce does, but that's probably just because the lights are not quite enough to support rapid growth in a larger plant.

I have not tried spinach yet, but it's on my to-do list. I have grown Malabar spinach hydroponically, but that is a vining plant and is technically not spinach anyway. I also have grown melon and squash hydroponically indoors before eventually transferring the young plant into soil outside.

Pictured are my seedlings I will be setting up in my kratky containers soon. Probably later this week. I will try to take pictures of the process.

Keep up the good work!

This is Jim's Thread and journal, and I don't want to hijack it with my journal. So I am documenting my latest round of Kratky lettuce on another thread.

https://garden.org/thread/view...

Two weeks in now on the original jars. I thinned to 1, 2 and 3 plants from left to right to see if there is much of a difference depending on heads.

Lettuce is looking solid. Keep up the good work!

How's that lettuce looking Jim?

I'll get another pic tomorrow. Growing well and real dark green. Can't believe the root system!

Yeah the root system is fun to watch. I don't know if it's basically the same size as what grows in soil or if it grows larger since there is no resistance to its growth. I'm starting some rainbow chard. I have grown plain white colored Swiss chard, but this is my first time with the colorful version. I have seen on YouTube the red chard having red roots. We'll see how it goes.
But yes, I find myself peaking in the box at the roots daily.

Day 21 of the first jars I planted.

They have really jumped since your last photo. What was it, like 5 days? Good work my friend!

Yesterday, I got everything seeded, fed according to the plant type and pH adjusted. I have five 3.5 gallon buckets on each shelf of a two-shelf rack, most with four 3" cups and two with two cups. Two, 100-watt LED strips per shelf. Lettuce, spinach, arugula, tomatoes, peppers, basil and sugar peas. That's enough variety to test the environment.

It's set up on an enclosed porch, so the air temperature is much like outside in the shade, meaning right now a high around 98 for a couple of hours. Because of the tough environment, I'm documenting closely and will start logging water temperature. And temperature in the seed sponge. I'm interested to see if evaporation modulates temperature.

If and when the tomatoes develop sufficiently to stand it, I'm going to run a temperature probe into the stalk at a branch point and see what's happening there. I see people doing outdoor hydro in high temperature and getting good yields, so I really want to know what the actual plant tissue temperature is to see if the plant is managing it when it's got a large water heat sink.

A plant that could evaporate without limit seems to be able to lower the temperature enough to make a difference. I'm not at all sure that the accurate wisdom about air temperature and the viability of soil-grown tomatoes necessarily applies to indoor hydro. For one thing a tomato plant in an outdoor container or garden in direct sun may well be hotter than the air and actually fruiting at a higher temperature than one would assume just from air temperature. Maybe there's a useful overlap between the tissue temperature of the outdoor tomato in sun and the indoor hydro tomato with plenty of water available.

It's said that 95 is the fruiting limit and 85 the color limit. I suspect a plant out in the direct sunlight on a 95-degree day may have a tissue temperature well over 100 when it's fruiting, depending on how much is can cool itself by evaporation. What I want to see is if in an indoor hydro situation, it can bring it's tissue temperature into the fruiting zone, which may actually be well into the 90's and not much cooler than the air on the porch.

I find studies, but they often grow in a control chamber but light with halide lamps, which run about 1000F and may well heat the plant above the air temperature they are using to report effect. There were root temperature studies, but nothing measured what was actually happening to plant tissue temperature.

There have been leaf temperature studies. Many are hard to apply, because the closely controlled test chambers are in no way similar to natural environments. But one study found that well-watered poplar trees reduced their leaf temperature by evaporation by 9C, which is about a change of 16F, enough that would bring a technically unable to fruit tomato down into fruiting range. Normally, they risk dehydration from doing it, but that's not a problem for hydros. A survey of studies found that plants in general can regulate their temperatures much as mammals do.

Oh, come on! You can't all have gone dormant back in July!
I've been looking everywhere for people to talk to about hydroponic vegetable growing. Did kale, chard and bok choy last winter, and now I'm getting adventurous.