Today's terrible tomato travail theorem.

When a deficiency in phosphorous exists, particular symptoms can include: Tomatoes:- Leaves dark green, purple underneath. Very slow growth.

I believe I suggested ventilation which would also carry off some of the mold inducing humidity.

An excellent suggestion, which I followed, with no change in the condition of the plants. The plants are not moldy, they are just spindly and listless-looking, with purple leaves.

Moisture and heat will generate mold. Wait for it.

So was the soil outside of your greenhouse as hot as it was inside? I doubt it, if there was ventilation.

Good luck.

You can drag them outside and spray paint the pots white. Use Fuse if they're plastic pots.

An excellent suggestion, which I followed, with no change in the condition of the plants. The plants are not moldy, they are just spindly and listless-looking, with purple leaves.

Why are you growing them in a greenhouse when it's summer? They do much better outside in the fresh air and even better when planted in the ground.

This is in northern California, on the coast, near the Oregon border. Outside daytime temperature yesterday was 64F at high noon outside,

First you tell us that the pots have the temperature of hot coffee. Then, that greenhouse is 80F and that it is 64F outside. There seems to be no way to get an intelligible answer out of you, so I bid you good day.

Billy, the pots were in direct sunlight yesterday. The thermometer was not. If these facts are not intelligible to you I will happily wave goodbye to you as you bid good day.

I have just returned from the greenhouse, where the air temperature is

You need to open up more ventilation in the greenhouse, and consider some shade cloth over the roof.

Omelet,

I have considered shade cloth over the greenhouse, but I fear that the reduction in sunlight would not be beneficial to the plants, We are in a coastal area and have fog and overcast a good part of the time. The problem seemed to be that when we do have full sun it raised the temperature of the soil in the pots (not the plants) too high. Shading the pots seems to be accomplishing this. I await further developments.

There is a large hatch in the roof and one at each end of the greenhouse. All three are open and there is no condensation inside. The only way to increase the ventilation would be with a fire axe.

Shade cloth is available in a wide variety of percentage filtering, one does not need to go to 95% shade when 40% will do. I don't know where you are on the planet but we are fortunate in SA to have such a wide variety available, and in different colours too.

Just trying to help...

I live in Texas and have greenhouses.

Omelet,

Are you on the Texas coast, or more inland?

Make it 1' to 2' above the ground.

A fan would help.

Central. Austin/San Antonio corridor.

Good idea! I concur.

Mine came with a thermostatically controlled fan. It also has two vents. I do not have anything in mine now because it gets up to 120°F if the sun is out even with the vents and door open. I have turned off the fan. No use in wasting electricity.

You could always raise cactus.