The seedlings started out great. A little over a month after they germinated, the branches began to fold upward and the leaves began yellowing with the veins turning purple. I planted more tomatoes at that time and they have been doing great.....dark green and dense foliage.

Thinking there might be a nutrient deficiency I've begun the past few days to water them with an organically based broad spectrum fertilizer. I don't see a drastic improvement so far.

So I'm trying to figure out what happened to the first batch. The stems are also purple at the base and green the rest of the way up.

First, the most common cause of yellowing in seedlings is over-watering and/or poorly draining soil. Especially likely when the yellowing is in the entire plant. Yellowing of new growth only indicates a nutrient deficiency, particularly N. Without knowing exactly what you used to feed I can't comment on that except to say if they are a couple of months old they are long overdue..

Second the purpling color is fairly common and a natural response of young plants whose roots aren't developed enough or are stressed, the temps are cool, or the plants are rootbound. Possible in this case if those are only 4" pots. It goes away as the plants mature assuming given proper growing conditions and usually poses no real long term damage to the plant. However avoiding stress is just as good for plants as it is for people. :)

The folding up leaves is also a a physical response of young plants to stress.

Causes of stress for young plants are many and impossible for me to ID from here without tons of details - air temps, soil temps, root development, amount of light exposure (they are leggy so odds are not enough), potting mix used, nutrients available, watering regimen, etc. etc.

I would "guess" they are over-watered, not getting enough light, and have limited root development for whatever reason. I'd lift a couple out of their pots and see if they are rootbound and if so transplant them.

Dave

These are 4" pots at the top but they are 6" tall.

For these three trays only, I used a seed starting mix of equal parts sand, compost, and peat moss. Because of the depth of the pots, and even though they have holes on the bottom, the bottom indeed seemed pretty soggy, so I drilled holes near the base of each pot to allow more air in. I also began watering only every three days starting a couple weeks ago. I re-potted a few of them into a mix containing vermiculite instead of sand a couple weeks ago, but they haven't improved. When I replanted them I could see the roots were nothing close to root bound. They were quite sparse in fact.

My greenhouse is in full Sun all day long. It is wrapped in 3.5mm Solexx which has 75% light transmission. I have other tomato starts of the same variety I started after these which are doing fantastic. The only difference being that I used a less dense potting mix.

Overheating is more of a problem than cold. The greenhouse hits 100 degrees most days even when it's in the low 70's outside. When the seedlings were young back in February, I even ran a heater on a thermostat at night to make sure it didn't drop below 65.

I assumed the compost would be enough to keep them fed until I planted. I mixed in worm casting with the compost. I'll keep feeding them the nutrients. I could switch to something specifically to helps the roots grow better. I get conflicting information....is it phosphorus or potassium?

Thanks again.

First, the mix you are using is not condusive to success with seedlings. Compost not only compacts in containers, drains poorly as you have discovered, but provides no nutrients to the plants because there is no active soil micro herd in the mix to aid in the decomposition or convert the nutrients in it to a form usable by plants. Compost and small containers just don't jive with each other well.

Add to that the sparse root development you have seen and "water-on-schedule-need-it-or-not" approach and you have the answer to the condition of the plants - the mix you are using and the over-watering.

I don't know why you elected to use the mix you did rather than one of the many classic soil-less growing mixes but you have unfortunately learned the hard lesson we all had to learn at one time.

If you are inclined to transplant your plants yet again into a quality soil-less potting mix, water them only when the soil 1/2 way down is dry to the touch, and set up a weekly feeding schedule of a 1/2 strength diluted well balanced fertilizer they will improve quickly.

What everyone who seems to be devoted to only organic nutrient sources needs to understand is that without an active soil web of beneficial bacteria, which don't exist in any container unless you add them, granular and non-liuid forms of organic fertilizers cannot work. Either switch to one of the many liquid organics or go with one of the synthetics and save the organics for after transplanting.

I understand the problems with temp control in greenhouses after my years in the nursery/greenhouse business. Unfortunately developing a way to control it is vital to plant health as either extreme is harmful to them. Automated systems are the ideal of course but many can't make that investment. But that doesn't mean you cannot and should not prevent the 100 degree days.

Ideal minimum is 45, ideal maximum is 65-70. Increase your venting, employ shade cloth, add a box fan for exhausting hot air and pulling in fresh cooler air, increase the air humidity levels, etc. are just a few of the temp control measures available. Much more info is available on the Greenhouse forum here.

Hope this helps.

Dave

PS: As any experienced grower can tell you, rootbound plants, no matter where you might see them or how they may appear to the eye, are never healthy plants. But that apparently isn't the issue here anyway.

I don't think overwatering is the problem. I water them with a nozel set to low on the shower setting for a half second in a 100 degree greenhouse. I think the problem is moisture retention. This particular mix may be too dense and is retaining too much moisture....especially at the bottom of these tall pots.

I'll proceed with the re-potting of these starts.

I very much appreciate the insight and suggestions. Thanks.

The sand was an experiment. After my last post I re-potted all 60 of the seedlings into my typical mix of 1:1:1 compost, peat moss, and vermiculite. The soil with the sand mixture was still crumbly--as I suspected it would be when I tried this--and it might work in shallower pots, but mine are quite tall and the soil was just way too soggy. It drained well, but the problem appeared to be that the sand left too small gaps for air to penetrate.

I can show you full flats of lush tomato starts that have not been fertilized once. Planted weeks after this first set but already larger. I understand what you're saying about the soil food web, but I think it's possible there may be enough bacteria and fungus in the mix of compost and worm castings to activate a soil food web and sustain a seedling through planting. If I'm wrong, then, great. I'm hoping to be wrong a lot.

I appreciate the watering advice.

I'm in the process of adding more vents to the greenhouse. It doesn't have permanent power though. I have a weather-proof inlet on the outside to plug an extension cord into with an outlet inside for running a heater or fan periodically. But the goal is to have the greenhouse be mostly passive.

Again, thanks for the replies.