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GpsFrontier 11-09-2010 04:16 PM


Couple folks recommended no more than 12 for the simpson
Not sure about any specific variety's, but are you sure it wasn't because of temperature? My lettuce grew fine on well over 12 hours, 4:30 am to about 8:00 pm of daylight, and never bolted until the temp got over about 85 degrees daily.

NorEastFla 11-09-2010 04:23 PM


Originally Posted by halfway (Post 5580)
Straight 12 and 12. My last batch of soil lettuce was at 14/10 and bolted early. Couple folks recommended no more than 12 for the simpson. It looks like the basil is fine with those hours as well.

From the research I've done, it seems that the amount of hours light won't have any effect on your plants bolting if harvested at the best time. Indeed, 24 hour light has been shown to increase yield/per/plant.

Here's one abstract of a study:

Title: Yield and quality of greenhouse lettuce as affected by form of N fertiliser and light supply

1. AuthorsZ. Premuzic

2. A. Gárate

3. I. Bonilla

Author Affiliations:

1.University of Buenos Aires, Argentina. Av San Martin 4453 (1417) Analytical Chemistry, Department of Natural Resources and Environment, Faculty of Agronomy Buenos Aires Argentina

2.Universidad Autónoma de Madrid Department of Agricultural Chemistry 28049 Madrid Espaă

3.Universidad Autónoma de Madrid Department of Biology. Faculty of Sciences 28049 Madrid Espaă

"Lettuce (Lactuca sativa) cultivar “mantecosa” with different kinds of light supply and different N fertilisation treatments was greenhouse grown. Three treatments were applied: two with N fertilisation: 1 – mineral fertilisation with 94 % Ca (NO3)2 − 6% NH4NO3; 2 – organic fertilisation with biostabilised compost and 3 – without fertilisation: control. Each treatment received two different kinds of light supply: 1 – 24 hours artificial light and 2 – no artificial light. Yield and nitrate content and vitamin C were determined in plants harvested at commercial maturity. 24 hours of artificial light supply improved yield and decreased nitrate content, but did not affect Vitamin C content. Both fertiliser treatments resulted in the same yield level. However, mineral fertilisation resulted in a higher concentration of nitrate in lettuce whereas vitamin C content did not differ significantly between all treatments."

Yet conflicting statements are in this report:

by Sherry Rindels, Department of Horticulture (Iowa, USA)

"Producing a successful lettuce crop can be a challenge for home gardeners. Weather is the main problem. All types of lettuce (crisphead, butterhead, leaf or bunching, and romaine or cos) require cool, moist growing conditions. Daytime temperatures of 70 to 75 and nighttime temperatures of 55 to 60 are ideal. Adequate supplies of moisture and nutrients are also important. Lettuce requires one inch of water per week. As with other plants, gardeners will need to water when Mother Nature doesn't supply sufficient rainfall. A complete fertilizer, such as 10-10-10, applied to the garden prior to planting should be adequate for successful growth.
Bolting is a common problem experienced by lettuce growers. Bolting is the undesirable formation of flowers and seeds. Bolting destroys the flavor of the leaves by making them bitter and tough. It is caused by high temperatures, long periods of high light intensities, and drought. Lettuce has an internal counter that keeps track of the number of daylight hours the plant receives. Once a critical number of hours are received, the plant sends up its flower stalk. The exact number of hours varies from cultivar to cultivar. Apparently, lettuce goes through four distinct stages of growth; juvenile/vegetative, adult/vegetative, adult/intermediate, and adult/reproductive. The plant can handle environmental stresses quite well when vegetative. However, once the intermediate stage is reached, environmental stresses, such as high temperatures or drought, will cause the plant to bolt.

Gardeners can reduce the tendency for bolting in various ways. Lettuce can be started indoors under lights to give them an early start and then planted outdoors while temperatures are still cool. When growing lettuce seedlings under lights, do not leave the lights on for more than 12 hours because lettuce needs short days to grow."

(end of quotes)


It seems that the intensity of the light is the determining factor in these two seemingly conflicting reports.

In the second study above, it discusses using the four stages of growth to determine harvesting times:

lettuce goes through four distinct stages of growth;

1. Juvenile/vegetative

2. Adult/vegetative

3. Adult/intermediate

4. Adult/reproductive.

As long as the plant is harvested *prior* to it's entering the Adult/Intermediate stage of growth, bolting would be avoided and the plant would grow faster and provide more yield if kept in 24 hour lighting.

For larger plants that are kept growing into and beyond the vegetative growth cycle, the decreased light hours would be a factor in it's bolting, along with humidity, heat and drought.

I would set up the plants for low levels of 24 hour/day light, (studies show that the low intensities don't effect vegetative growth much), and plan harvests on the last days of vegetative growth with short crop cycling to optimize efficiency.

That way, yield is increased, bolting is eliminated and lighting efficiency is maximized by using the least intensity but longest hours.

Mind you, for me, this is just theory based on studies. I've yet to grow indoor lettuce, so my tests this coming year will show the real results.

I'm pretty confident that these folks know what they're doing, and have reported accurately. I'll have to let you know in a few months.

halfway 11-09-2010 04:46 PM

That is a consideration GPS, but the previous location for the soil lettuce indoors had a fan on it as well.

The length of day was somewhat validated by the hydro store grower who presented a case of early and late season lettuce growth when lite cycles are below 12 hours a day. Even less cosidering angles of the sun. It made sense.

After some researching on the net, I could not find anything as comprehensive as what Nor posted, but the info I did find confirmed and prompted to me to adjust to the 12 hour cycle.

I agree the article presented is very convincing and I have no reason to doubt it. I may do some further experimenting. Not sure I can split out a test set at this point though.

Thanks for the input guys, very informative.

NorEastFla 11-09-2010 05:07 PM

As with most flowering plants, the plant will enter the flowering stage naturally when conditions favor it as the next cycle of natural growth, *or* when stress is present that *forces* it into the flowering stage of growth.

The ending of the vegetative growth stage can be forced by heat stress, drought, very high mold causing humidity or plant damage. The plant "sees" these factors as a likely cause of it's death and responds by throwing itself into a *survival* mode of instant flowering to propagate it's species and make it's life worthwhile in plant terms.

If none of those factors are present, then the natural timing for each sub-species of plant type would determine the initiation of the flowering cycle.

Keeping those factors within tolerable levels for the plant and learning the plant types natural flowering time in days would be the key factors in eliminating unwanted bolting in lettuce it seems.

halfway 11-09-2010 06:37 PM

I look to begin harvesting leaves on about the first week of December with the middle of December being the "expected" full harvest as noted on the seed package.

Can't wait to see how they react to full nutrients in a week.

This will be the first full nutrient changeover....anytips or cautions?

GpsFrontier 11-09-2010 07:20 PM

I understand not wanting to change anything half way (no pun intended) through a test. I just thought I would add some things to the discussion. I have been wanting to move to Alaska for decades, even wanting to start my hydroponic farming operation up there (haven't made it yet). But I am still always interested in anything about that state. It's well known that Alaska is the "land of the midnight sun" and grow very large produce due to their 20-22 hours of daylight.

I would agree completely with NorEastFla, that the stress factors are key to lettuce bolting. I did a little searching and found some things on growing lettuce in the land of the midnight sun. Keep in mind they refer to growing in soil not hydro, but they are talking about growing lettuce in nearly 24 hours a day of natural sunlight. I have not read them all, but what I have read the issues are dew to stress. There is some reference to length of light being a problem. But that's dew to higher nutrient depletion from the soil in long daylight periods. That's a stress factor that can be easily remedied in hydro.

The Voice of Agriculture - American Farm Bureau
"Paul Huppert put down roots in Alaska and soon learned the secret behind growing tender good-tasting cabbage, broccoli, lettuce and potatoes. "Well actually, we have daylight practically all the time from mid-June on," said Huppert, the patriarch of four generations farming the rich Matanuska Valley. "We have 20-22 hours of sunlight and consequently that plant doesn't take a rest at night; it just keeps growing.""

""We can grow a crop of head lettuce in 60 days," says Huppert's neighbor, Ben VanderWeele. "The same crop of head lettuce, same variety, same everything, takes 90 days in the Salinas Valley in California, which is supposedly the best of the best.""

Alaska Mixed Vegetable Profile, in pdf. http://www.uaf.edu/ces/publications-.../FGV-00040.pdf
"Although there are numerous difficulties involved in high latitude vegetable production, the 100-day growing season is augmented by long daylength, which allows for high production under irrigated systems."

"Head Lettuce production of 22,100 cartons were harvested from 52 acres in 2005. Average carton weight for Alaska grown head lettuce was 45 pounds, yielding approximately 497.25 tons of product"

"Sunlight is a major factor in crop production in sub-arctic Alaska with near-continuous light prevailing from mid-May through mid-July, followed by long but decreasing photoperiods through the end of the growing season."

"Lettuce is susceptible to tipburn, a disorder where the edges of some inner leaves die from a localized lack of calcium that is related to uneven water transport. Water stress can lead to tipburn damage during the long days in June and July in Alaska." (nutrient and water stress problems can easily be avoided in hydro)

"Lettuce is sold in cartons that usually have 24 heads and weigh approximately 45 lb." (that's 24, 2 pound heads, heavier than what I usually get at the store)


Here is a study on greenhouse production of tomato and different types of lettuce northeast of Fairbanks AK. There is some reference to using different cultivators for summer and winter in this ongoing study.


P.S. I wouldn't go full strength with the nuts yet, for me the plants are still to small to make it worth it. I would stick to half strength for another week or two. I always quickly wash out the reservoir with a soapy sponge and rinse thoroughly, as well as clean the pump and filter with each nutrient change. That makes it less likely for any pathogens to get a foot hold in the system (as well as any algae buildup). I also flush the system with plain water, then dump that before I add the fresh nuts. When my lettuce was just seedlings like that I went 3 weeks on 1/2 strength nuts, because plants that small don't take up much nutrients at all in comparison to the later stages of growth. And the look of the nutrient solution was still a nice translucent color with no cloudiness. Also I was running low on my supply of nutrients so I wanted to stretch out how long they would last.

halfway 11-09-2010 08:15 PM

Very timely info and well appreciated. I recall reading about the record setting produce because of Alaska's long day growing season.

I think I will up the daylight to 14-15 hours per day and watch for effects. As I think about it, this first batch is fine to tweak.

Thank you for the "experience" with the nutrients. I will take that advice. Same with the "flushing" you recommend.


NorEastFla 11-09-2010 10:46 PM

Something you may want to keep in mind is the harvest timing referred to on seed packages is in reference to traditional soil grown, outdoors gardening under natural sun.

Hydroponic farmers have found that it's much more efficient to grow for only 4 to five weeks on lettuce crops to maximize annual harvest weights. That allows for more crops per/year and radically increases the annual yields by weight.

You would be much better off growing for only 4 to 5 weeks under 20 hour lighting than trying to grow for the time span set for full grow soil gardening.

Just plant more head, more often. The rows can be spaced tighter as well.

The *young* lettuce is also more tender and more of each leaf can be used without the pith or woodiness of end leaf full sized soil plants.

tamsterg 11-18-2010 07:37 PM

I found some great easy to follow videos on you tube published by SureToGrow. They are also posted on hydroveggies.com website under educational links.

halfway 11-19-2010 12:01 PM

Video Update
Thanks for everyone's input to my learning curve.

Latest video update. Awesome. Thanks for the note Nor East about keeping nutes till week 3 as opposed to my original plan of 2 weeks, I believe I will continue this process for these veggies.

YouTube - Hydroponics Growing System 19 Nov 10 Ebb and Flow (Flood and Drain) Hydroponics

GpsFrontier 11-19-2010 06:15 PM

Thanks for the video update, your plants are looking great. Those roots have a nice healthy white color to them also. That's just about the size my lettuce was when I switched them over to full strength. What does your friends and family (the die hard dirt growers) say?

P.S. I'm curious, what did you decide on for a lighting cycle.

halfway 11-21-2010 09:32 PM

Dulling Root Color?
Ok, replaced the spent solution with clean water and let it "rinse" the system for 24 hours. I emptied that and added fresh water with full solution this morning which is at the 3 week mark.

I think it was time as some of the new growth on the basil is lighter green than they should be.

I also notice the roots of both the lettuce and the basil are not nearly as white as they have been.

I do not see any other signs of distress in the roots or the veg growth.

Should I be conserned with the dulling of the roots from white to almost a brownish haze?

Thanks in advance.

GpsFrontier 11-21-2010 11:04 PM

I always try to stress observation of the plants as the most important factor in knowing how they are doing. Just like you noticed the leaves starting to become yellow. I used to mark when I changed the nutrients on the calender, and/or added anything to it (and still try to). But after forgetting so many times, I mostly just rely on observation to tell me when to change them. Although knowing when it was changed last is still important, because as you get used to knowing how long the plants can go without problems (including pH swings), signs of early problems can be a singe of other issues.

The roots looked nice to me. Although I did see some slight brownish, but that is not necessarily a sign of any problems. Older roots will tend to become brownish naturally, also the nutrients in the solution tend to stain the roots the older they get. As long as you are continuing to get good new growth, and the new roots are continuing to grow out white, and the older roots are not turning dark brown, as well as the tops of the plants are looking good, then that wouldn't be anything I would worry about.

If they do start to turn dark brown, the two major factors that I know of is "lack of oxygen in the water", and "excessive nutrient temperatures". Of coarse dark brown mushy roots could be caused by pathogens that can cause root diseases also, as well as fungal diseases, but I have not ever come across that specific problem. Like I said, I clean and flush my systems to prevent that sort of thing. But I have dealt with "excessive nutrient temperatures" (I live in the mojave desert). But I would consider the two major factors first.

I always keep an eye on the nutrient temp just in case, it should be be between 68 and 72 degrees Fahrenheit optimally. Above 80 and your likely to see signs of browning as well as dissolved oxygen loss in the water. Below 60 and the plants wont be able to absorb the nutrients as well, and your likely to see signs of stunted growth. Because I grow outside my nutrient temps have ranged from 110 in summer, to about 38 in winter, so I have seen extremes and dealt with both.

I also add H2O2 (hydrogen peroxide), not really for pathogen/fungal control, but for adding extra dissolved oxygen. But it can help reduce the number of pathogens in the solution also if you ever come across it. I use 1 tsp (5mL) per gallon each week (when I remember). Sometimes I forget when I added it because I didn't write it down, so I will wait to add more so I don't add too much in too short of a time.

P.S. Just thought I would mention that when I flush my systems with straight water with each nutrient change, I usually just run it through a couple of cycles (30 min each or so). Then sometimes I empty that out and do it again, before emptying that to add the fresh nutrient solution. But I don't think flushing it for 24 hours will hurt anything.

GpsFrontier 11-23-2010 05:48 PM

8 Attachment(s)
Just thought I would post a some pictures of brown roots that were caused by excessively high nutrient water temp. If I remember correctly the nutrient temp was in the upper 80's and low 90's at the time of the pictures. They are the roots of the strawberry's that I grew 2 summers ago, and the pictures were taken in either late May or early June. Our temps in early June reach in upper 90's and by late June they are in the 100's (I grow everything outside). I sent the pics to General Hydroponics tech support, who told me it was caused by the nutrient temp. That's when I first learned that the nutrient temp was important.

I then froze blocks of ice to cool down the nutrient solution with, I then saw new roots coming out a nice white like they were supposed to be. I needed to add ice blocks twice a day, once in early morning, and again in mid afternoon. Even so, the nutrient temp would fluctuate and I couldn't keep it within range constitutionally. By early July the daytime temps constitutionally reach the 110 degree mark, and I was simply not able to keep up with freezing the amount of ice I needed. With all the containers of water jam packed in the freezer absorbing all the cold, the ice creme was getting soft and melting (even on the highest setting). So I gave up on my first summertime attempt at hydroponics.

I know you are growing inside and are very unlikely to see anything like those nutrient temperatures, and I didn't post the pictures to scare you. But I had the pictures, and thought it might be helpful to see what happens when the roots of a plant are constitutionally subject to high temps for future reference.

halfway 11-23-2010 07:24 PM

Very helpful post and it doesn't scare me in the least. That is good to know because mine are just lightly brown. It was enough to notice after they had been brilliant white.

Thanks for sharing the experience. I believe your "underground" water holding tank is designed to offset the heat right?

GpsFrontier 11-23-2010 10:51 PM

Ever scene I had that problem, I have been on a quest to find economical ways to cool the nutrient selution. The in-ground reservoir (geothermal reservoir) was the only realistic economical option I found. Just about every other option involves using a lot of electricity, and with $700 electric bills during summer (because of running AC 24/7) adding much more to the bill is not really economical for me. The design works as intended with ease of use in mind. Although I never really finished it. I had planed to build up the above ground portion because I was not able to get the hole as deep as I wanted (too much rock in the ground here). I also never really completed insulating the above ground tubing, and plant buckets that I Had intended to do. But never the less, the nutrient temperature remained pretty constant between 80 and 84 degrees thought the hottest part of the summer (late July and August), and I never added any ice to it at all.

That's about 10-12 degrees warmer than perfect. So despite the fact it could have been better if I didn't get lazy, I think it preformed quite well. I also know next summer I can make it better by not being lazy, and finishing up the details. I also have two new ideas to test next year. Both work on cooling by evaporation, but in different ways. One is relativity easy and inexpensive to build. The other will take some more research, as well as small scale testing and refining in order to see if it's feasible and what it would take on a larger scale.

The first one was built by a guy in Phoenix where they get the same type of daily temperatures we do here (phoenix is about a 4 hour drive), and he clams it works well. He sent me pictures of it with details, but I don't want to post his pics because I never asked if he would mind. But When I build it I will be happy to post all the details of how I did it. Also I may draw up some 3-D pictures to post asap for people if there is any interest.

halfway 12-06-2010 06:46 PM

Time for an update.

We have been steadily harvesting over the past few weeks and the lettuce and basil have been excellent.

I didn't see a noticeable change with lighting above 13 hours so that is where I have kept it. The lights remain about 2-3 inches above the plants and the fan pushes the little heat generated out of the way. Without the fan it hits around 82 degrees, with the fan it stays around 68. Perfect for crisp, tender greens.

The browning in the roots I posted about earlier still remains, but many new and bright white roots have grown around them and from the sides of the pots. I may have created a little root shock OR it occurred from holding the nutrient change from 2 weeks to 3 weeks. The plants were not effected at all, so I will remain at 3 weeks for initial nute changes with lettuce in this system. I did notice a slight decrease in color at around 20 days, so 3 week nute changes it is.

Since 5 pots grow Simpson lettuce and 1 is growing basil, I have a need to keep crops in rotation as discussed by hydrogardener here and in HIS blog. He has a great system that I am using as somewhat a template for keeping us in rotation. Many others' methods are incorporated as well.

I am building 2 DWC systems for lettuce rotations and still debating the future use of this ebb and flow. The determining factors include the size of plants as I need to keep the floros on them at a uniform spacing. Keeping the basil horizontal is a challenge!!

Here is a pic from November 27th. This is after many harvests.


GpsFrontier 12-07-2010 05:54 PM

Hello halfway,
Sounds like the plants are doing good. I'm not surprised at the basil, the basil that I grew got about 1 foot tall and 1 foot wide before I pulled the plug on it because I wasn't able to keep the nutrient/water temperature under control any more, so I'm not sure how big it would have gotten. 68 degrees is a great temp for growing lettuce. I wish I had a basement where I could grow year round lettuce greens like that.

Just wondering, how deep is the water culture systems for the lettuce that your building planed to be. Mine did great in a regular water culture system, with the water only being 3-4 inches deep. Although the deeper it is, the more of what I call buffer water (nutrients) there will be. That could allow for longer intervals between nutrient changes, provided you keep them fresh by not allowing to much algae and other things like unwanted pathogens to grow in it. Good aeration of the water, water circulation, blocking light and keeping the water in the right temperature range will help a lot in keeping them fresh as long as possible. In a water culture system (deep or not) when there's no water pump circulating water, an air pump and bubbles from air stones keep the water moving (circulating), as well as aerate the water. So the more bubbles, the more movement the better. Especially when trying to keep them fresh for longer periods. But for me, I don't think there's a need, or even much benefit for it being deep just for lettuce.

halfway 12-08-2010 07:52 AM

Thanks for the input GPS.

The totes are 8 gallons each and the nutrient level all said and done will be at about 5.8 gallons. The volume was of concern for the very reasons you stated (stability/temperature).

The air pump and stones I will use are all large capacity. I had the pump on hand from a large fish tank.

Now to get the holes cut..........

GpsFrontier 12-08-2010 04:37 PM

No problem halfway, sounds like you have planed it just about like how I did mine. http://www.hydroponicsonline.com/for...th-system.html

Mine held about 6 gallons of nutrient solution in it, but because the tote is wide and long, the water level was not deep. I'm not sure what shape your new totes are but I am guessing their about the same as the ones I sure, and/or like they ones your using now. I was thrown off by the term DWC (Deep Water Culture), I don't really consider it deep until the water level is about a foot deep. Good luck with the new system.

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