That is quite correct, Dorothy. The amount of water a plant will need depends on how much of it there is to support (if that makes sense). A fully herbaceous plant that has completely died back will need very little water for a long time but an evergreen plant, such as a shrub, still has a lot of living material to just keep ticking over and hence will need more water.
Badly explained answere, sorry.

you also have to remember that many plants that are not actively growing [dormant] will be affected by the cold too.

The snag is our plants have been under frozen snow for three weeks... the top few inches of soil are also frozen. Now if it starts to thaw tomorrow it will still take weeks for all the snow to actually go - unless it suddenly gets really mild and the snow sublimates rather than just melting. Meanwhile with the top inches of soil frozen any melt is not going to get into the ground. I only have to look at our rhododendrons to know they are short of water. The leaves are all hanging straight down. Once the snow goes and the soil warms then they will start to life again.

I am concerned for the likes of our crinodendron which suffered badly last winter when we had frost in the ground for a month. It basically lost most of its leaves and the flower buds dropped. It has recovered but this weather will stress it again. If a plant is stressed too often and for too long it eventually does not survive.

fingers crossed for you then mg.

Thats sounds bad MG as a lot of plants were stressed over the dry summer. My Rowan was very stressed this year and had lost all its leaves by August so this will not be helping it?

Well Drc assuming it got a good drink between August and now your rowan should be fine... Its rots will go down further into the soil and so it should still be pulling up water.

SBG thanks - we also moved some acers in December and are both worried that they had not had time to establish before this weather set in... oh well much as I love and cherish every last plant and friendly grub/bird in the garden have to accept that nature rules!

Do hope it will be ok but as you say its nature!

If the comment you were commenting on came from me, then to a certain extent I was talking about alpines rather than general herbaceous plants. Many alpines especially those used to snow cover, are never truly completely dormant and they rely on the small but constant amount of highly oxygenated melt water to survive.
Having said that, many soi dit dormant plants still need a certain amount of water, albeit a tiny amount. Probalby the only ones which can survive cold drought are bulbs and those plants from parts of the world where frozen soil down to the depth of the roots is common.
We have had fairly severe frosts here, but when my wife managed to get a fork into the ground to get out some leeks, it was only the top 2 to 3 inches which were in any way frozen, below that the soil was cold, admittedly, but still soft. Guess where the roots of most garden plants are?

Should add, that when we lost so many plants to cold drought, the frost actually lasted from mid Novemeber to the end of February without ever unfreezing.

Thanks I find this interesting as I had never really considered the water needs of plants in winter before.