Lettuce growing very slowly; brown spots on leaves

[Dennis Jay]

My system has been fully cycled for six months, but still not getting good growth out of most of my plants. Any suggestions would be welcome.

The system:

50 juvenile largemouth bass in 330 gal tote.

12' x 2' x 12" grow bed with hydroton, cycling every 18 minutes.

System is inside greenhouse with grow lights.

Water tests are pretty consistent with pH at 6.5; ammonia at .25 ppm; 0 nitrites and nitrates at 160 ppm

Temperature stays between 60 and 70. Higher on sunny days.

Humidity is high at 80 to 85%

I add a bit of liquid iron and potassium about every two weeks.

The problem:

30 days ago I planted lettuce seedlings. They grew for a couple of weeks and then very little growth since then. Some leaves died off. Others have brown and black spots (see photo). At the same time, I also planted a few seedlings in dirt. They are now about double the size of the lettuce in the grow bed.

Thinking that the lights might be too harsh on the plants, I moved them up to about 18" above the plants. I'm also thinking that there may be too many solids entering the grow beds (even though I have several hundred red worms), so I began filtering the water.

The fish are doing great, and they've about doubled in size in the last 60 days.

Anyone have any ideas? Thanks.

[Jonathan Kadish NYC AA Chair]

If you did have leafspot you will continue to have issues with leafy greens. If these basil have a hard time growing and the spots continue to manifest then you do have the bacteria in your system. Transplanting can be the source of the infection... from here on out I would recommend that you take a hard line and not introduce any possible threats to your bio-security. This means only starting plants from seed. If you continue to plant leafy greens the bacteria will remain indefinitely, you may have to forgo growing any type of plant that gets infected for several months.

[Vlad Jovanovic]

Holy Moses Dennis...that substrate that the basil sprouts are in seems way, way too wet. Is it like that often? Things being too wet and too crowded like that is usually a real good breeding ground for pathogens. Really, the roots of seedlings should never be allowed to completely dry out... that's it. That's all you really have to watch for. Keeping things too moist or wet is usually a bad idea.

Dennis Jay said:

Thanks for all of the advice. I've pulled the lettuce out — about 100 plants and replaced with some tomato plants that have been growing in dirt. I've also installed a fan, which has helped to lower the humidity by 5 to 10%. Some of the other plants — mint, okra and peppers — are doing fine. But some basil seedings I've been sprouting in dirt have developed dark spots (see photo). Is this anything to be concern about? I've also attached a better photo of the infected lettuce. The fungus has a dark and silver color to it.

[Dennis Jay]

Everything I have planted in the last several months has been from seed.

Jonathan Kadish said:

This means only starting plants from seed. 

[Dennis Jay]

It doesn't often get that wet, but it's obvious I overwatered. With humidity in the 75 to 80% range, nothing seems to ever dry out. The fan is helping, and on warm days, I keep the greenhouse door open to allow dry winter air in. Thanks again for all of your astute advice.

Vlad Jovanovic said:

Holy Moses Dennis...that substrate that the basil sprouts are in seems way, way too wet. Is it like that often? Things being too wet and too crowded like that is usually a real good breeding ground for pathogens. Really, the roots of seedlings should never be allowed to completely dry out... that's it. That's all you really have to watch for. Keeping things too moist or wet is usually a bad idea.

Dennis Jay said:

Thanks for all of the advice. I've pulled the lettuce out — about 100 plants and replaced with some tomato plants that have been growing in dirt. I've also installed a fan, which has helped to lower the humidity by 5 to 10%. Some of the other plants — mint, okra and peppers — are doing fine. But some basil seedings I've been sprouting in dirt have developed dark spots (see photo). Is this anything to be concern about? I've also attached a better photo of the infected lettuce. The fungus has a dark and silver color to it.

[Jonathan Kadish NYC AA Chair]

I thought you said you took tomato plants from dirt and put them in the system... that could be a source for pathogens if the bacteria was in the dirt.

Dennis Jay said:

Everything I have planted in the last several months has been from seed.

Jonathan Kadish said:

This means only starting plants from seed. 

[Vlad Jovanovic]

Part of the advantage of any soil-less growing system is not having to deal with dirt born pathogens or pests. why would you start plants off in dirt, and then transfer to AP? I've sprouted thousands of seeds in just hydroton...and have a wonderful germination rate. All the stuff you see in my rafts were germinated directly in net pots filled with hydroton. I just don't put them in the DWC trough until about 10-15 days after they germinate, but they all seeds start off directly in hydroton. This has a number of advantages.

1). There is no transplant shock for the seedlings Since the seed is started in the same place it will live out it's life, so no waiting days and days for them to get over transplant shock and start growing again. So better for them.

2) It's a HUGE time and energy saver. Transplanting seedlings sucks IMO and is a totally un-necessary waste of your time/labor in most AP scenarios. So better for you.

3) It's also cheaper that way, since there is no coco-coir, vermiculite, perlite etc...to buy.

4) No soil born pests or pathogens (even in bagged and bought products I've often come across various larva and who knows what else that you can't see...fungal/bacterial).

Starting seeds off in soil, or any other medium, seems pointlessly time consuming, counterproductive, more expensive, and doesn't give germination results that are any better than starting them off in a LECA media, and can be the source of many a pathogenic headache.

[Roger Baldwin]

Vlad I agree with sowing seeds straight into the LECA. There is a very high germination rate,  At my nursery we start many vegetables in professional seed starting mix to sell to customers and the germination rate of the starter mix is not as high as the AP grow bed (flood and drain).  That doesn't even address the time and energy saving aspect.  Also I have seen MANY things in "sterile" bagged goods, like seed starter mix, that should not be in there, centipedes, grubs, bits of shredded plastic.

What is the problem with placing them in the DWC to germinate?  I am starting my first DWC bed and just getting ready to sow my seed, what do you recommend?

[Vlad Jovanovic]

I'm not saying that there will necessarily always be a problem, but I'm a really, really firm believer in not keeping things overly moist at the young seedling stage...floating the 'youngins' 2 maybe 3 times a day for 10-15 minutes at a time is plenty for me. of coarse this will depend a bit on your location (heat/light). I can't remember the last time I saw a bout of pythium, collar rot, crown rot, root rot etc...

Actually, I like to somewhat air-prune my seedlings for the first 10-15 days. 

[Roger]

I'd watch out using H2O2 in your AP system.  It is a disinfectant that will kill that bacteria in your bio filter.  If you do use it try to cover the top of your GB so none of it enters your AP system.

[Roger Baldwin]

Makes sense. but aren't more mature plants more susceptible to such ailments because of the lack of light and air penetration? I plan on keeping the top of the LECA dry by elevating the net pots with the blue board. And also I am a big fan of circulation, I have a HAF(horizontal air flow) fan constantly blowing across my GBs. I will try to germinate straight in the DWC tank for this go around, but I will keep your recommendation in mind if i encounter problems... That's one good thing about starting small, it makes it easier to experiment.

[Dennis Jay]

I started the plants from seeds in dirt and didn't buy them as seedings. You're right about this being a source for pathogens. 

Jonathan Kadish said:

I thought you said you took tomato plants from dirt and put them in the system... that could be a source for pathogens if the bacteria was in the dirt.

[Bob Campbell]

What is a good strength of H2O2 to use?   I just looked at the bottle of Hydrogen Peroxide I bought at the drug store and it says 3% topical solution.  Would you dilute this or use it straight?

Jon Parr said:

I would personally mist the plants and surrounding area lightly with hydrogen peroxide to kill spores while handling, and to help prevent any spores from going airborne. No big deal, but H2O2 is a relatively safe disinfectant, and leaves nothing behind but water and oxygen.