Do most plants lose their leaves over the winter?

I put several plants in my greenhouse to overwinter and almost all of them lost their leaves. Is this because I didn't take care of them (we had serious white flies) or do they naturally do this? Almost all of them came back to have a new healthy life this spring. I just didn't know if I could do anything to avoid them losing their leaves. And if so, what? Especially the white flies? Is this just the curse of having a greenhouse?

The plants include: mandevilles, tropical hibiscus, lantana, tuber begonias, and dahlia.

Thanks!

I don't grow the begonias and dahlias so I'm not sure if those would normally keep their leaves or not, but all your others should keep their leaves if they're happy with the conditions. The other thing besides the pests could be the temperature--how warm did you keep the GH? I know that mandevilla, hibiscus, and lantana will all lose their leaves if the temperatures get low enough--I keep my GH at 55-ish and they all keep their leaves, but when I've had mandevilla and hibiscus outside wher the nighttime temps are regularly in the 30's they'll often drop their leaves but then come back in the spring (get too much below 30 for too long though and they won't come back). Lantana usually keeps its leaves to colder temperatures than the other two but I know when mine get enough frost they'll sometimes lose their leaves too.

Mandevilla, hibiscus, and lantana should all keep some or most leaves through the winter. Control of whiteflies will help.

Sometimes the stress from moving a plant from one environ to another can cause it to drop leaves. I inherited a massive holiday cactus that lost all but the woodiest of growth, and then every time it grows new segments, after about 3 or 4, they fall off. It had spent years in one spot of a house, and just won't be happy in the GH. All my own holiday cactus–strong and healthy growers. My experience is much like ecrane3's. If the temps or pests aren't the problem, then maybe water / humidity are lacking.

White flies, like mealies, aphids, etc., are controllable, however you have to be careful and vigilant. Prep the plant to remove most pests before you bring them in. I prefer to not use chems, but I have heard of fogging them. I spray the plants off with the hose. Then, use isopropyl alcohol and spray the plant down, esp. where leaves meet branches and branches meet trunk. Hose off the isopropyl immediately.

If you use chems, you can spray with that, or systemically. I have used sticky yellow cards. I think I bring in some spiders on some of the plants and they feast on the mealies, etc. all winter long. I might chem. spray some of the larger plants which get mealies without fail before I bring them in this year.

I moved a large group of outdoor plants into the greenhouse just a couple of days ago hoping to overwinter them and save costs on plants for spring of 2009.

Angelonia, German Ivy, Coleus, Ornamental sweet potato plants and took cuttings also, Vinca. I am in hopes they will all keep their leaves and that I will be able to propagate alot of them for more plants in my gardens for 2009. What do you think...will it work?

Sounds like a good plan, or experiment, at the very least.

Just watch carefully for mealies, mites, aphids, etc. Getting them before they are a problem are key.

Will be interesting to see how well you fare ..... yard sale in the spring for the extra plants, I predict!

I am about to try to make some cuttings of holly. MIght construct a small cold frame around them to protect them for the winter.

i have a 8x12 soldex greenhouse. I live in 8a. I just try to keep the plants barely alive in the winter. I don't water them unless they are wilting. Sometimes they look a little unhealthy but I only lost some coleus that I shouldn't have tried to keep anyway. In spring I trim them back , clean them up and fertalize. I grow lots of geraniums and a few semi tropicals. I have a small electric heater on a timer to turn on mostly at night. No bug problems