What causes Tomato plants to drop their leaves?

[Leeds_lad]

Here is the latest casualty. This is the variety Cherokee Purple. As you can see, no sign of disease or anything, simply dropped off it's entire leaf stem.

[Leeds_lad]

Some of my tomato plants are a bit purple (I read this is due to a phosphorous deficiency due to cooler temperatures) but not the ones that are actually dropping their leaves.
You reckon any of this could be a factor?

[Creemteez]

Don't know about the phosphorous, Leeds lad, though as they are relatively young plants in good quality compost, they shouldn't be lacking anything at the moment.
As the leaves are dropping so suddenly, and looking at the remaining stalk on one of your pictures, I suspect a "bug" of some kind! It looks like the stem may have been eaten through! Check the underside of your pots for ANY animal life. I've had mystery holes appear and leaves drop off for no apparent reason, only to find the culprit (usually the teeniest of slugs) lurking on the bottom of the pot! It's also worth slipping the rootball out of the pot as sometimes they hide just inside the drainage holes.

[Florence Fennel]

How very odd. I hope you get to the bottom of this LL, it would be interesting to know what it is.

[Leeds_lad]

Don't know about the phosphorous, Leeds lad, though as they are relatively young plants in good quality compost, they shouldn't be lacking anything at the moment.
As the leaves are dropping so suddenly, and looking at the remaining stalk on one of your pictures, I suspect a "bug" of some kind! It looks like the stem may have been eaten through! Check the underside of your pots for ANY animal life. I've had mystery holes appear and leaves drop off for no apparent reason, only to find the culprit (usually the teeniest of slugs) lurking on the bottom of the pot! It's also worth slipping the rootball out of the pot as sometimes they hide just inside the drainage holes.

AH the remaining stalk that the picture shows is not from the one that fell off, it's from what remains of another stem I cut off (and badly at that =p). The entire leaf stem simply falls off right from the main plant stem. I inspected the area it came from, no disease there or nothing, a pretty healthy looking plant.

[Leeds_lad]

Well about the phosphorus, It's not that the soil doesn't contain it, it's that if the plants are kept too cold and wet for a while the plant has a hard time getting it from the soil. I honestly thought a purple tint on the plant stems and under the leaves were due to the variety until I researched it =p. Let's just say the ones who were showing it are snug as a bug now.

Now onto the mystery of the dropping leaves