One might assume then this sunroom is not a 4-season room and there is some reason why it cant be turned into one.
If its not part of the main house==i.e. has a basement, then you are dealing with cold floors that makes it unable to be used when the temperature drops.

Since you stress the amount of light reaching the room is limited, then that puts a definite limit on what plants you hope can do well. But, in that regard there are many.

With any plant that is said to be "for a particular temperature range" there are no guarantees. Plants thrive when given what they would be given in their natural state.
Since most houseplants are tropical in nature, then we have to try to emulate those conditions. In the modern furnace- on-house, that can be daunting. The amount of light they receive is one of the most reasons hard to come by. But houseplants, after being given an amount of time to cope with the new conditions, will adapt usually well.

Plants can be moved to the light. We are aware that certain exposures are best for certain plants at certain times. A southern and western exposure gives us the light that is usually said to be full. In those directions, we can reliably be certain that --barring any obstruction such as trees, shrubs and other buildings, that we can obtain at least 6 hours, probably more, the plants can use --if they are of that ilk.
The morning sun....from the east, if a plant is given at least 2 hours of full light from that exposure, most plants can survive well. Put a plant that requires full sun there and it wont do as well. The first sign will be probably poor flowering, not as sprightly growth.

A mini-greenhouse effect can be obtained by placing plants where they receive reflected light...say from painted walls.
Plants that are raised to obtain the best amount of light can often support plants that would not do as well if put on a table or on the floor.

But that room with temperatures approaching 40's is not a room I would suggest a plant be kept in. Not even those plants that prefer cool nighttime temperatures will survive long if kept in such conditions. Nighttime temps are usually said to be in the range of 60 - 70º.
When the house is MT for an extended time, and the houe is put at 55º on the thermostat, plants might survive well when grouped together and assured they are watered sufficiently to ward off any hint of frost.
Then again, some plants, such as Christmas Cactus, are given low temps on purpose...into the 40's, to set their buds before being taken into a sunny window indoors.

As far as books for houseplants----can you count that high.
First place to look is at your local USED bookstores.
They are always exhibiting garden books and are certain to include houseplants....some with pictures.
These books are usually---no, no, always much less expensive than retail. Book publishers are forever advertising their books on pretty well everything.....and gardening is at the top of the list.
I suppose cooking books would be right alongside.

I would recommend going to the library and read up on houseplants, then decide which books to get. I love the old Reader's Digest houseplant book most. I can't seem to find mine so I don't know the title, but it's something like "Success with Houseplants"

There is no reason why some plants can't be grown in 45* I know this is cold for most plants, but as long as the roots are fairly dry, a hoseplant will take a lot more cold than any book will tell you. It's the wet and cold that does them in more than just the cold.

Hey Mentha,

Great minds think alike:

it's called Reader's Digest Sucess with Houseplants.

I got mine in '95, think I paid $22 for it, something like that. One of the best investments I EVER made -- I love this book for ALL kinds of reasons. It's my one home reference books & has gotten me through SOOO many plants!

Hey Mentha,

Great minds think alike:

it's called Reader's Digest Sucess with Houseplants.

I got mine in '95, think I paid $22 for it, something like that. One of the best investments I EVER made -- I love this book for ALL kinds of reasons. It's my one home reference books & has gotten me through SOOO many plants!

Ooops, so sorry for the double post, pardon me!

PG,
I got mine at goodwill for about $1. It was the best investment I've made. Speaking of goodwill, that is also a really good place to get books, also try a used book store. I don't like paying full price for anything, and if I can find it for cheap, I'm happy :)

chris, I don't know that it would be possible to obtain all of the best temperature information from just one book or website. You are right: there IS so much conflicting information.

Though I have a large collection of plant books (including the Reader's Digest one mentioned!), I find that I rarely turn to them anymore. I usually opt for a google search on a specific plant and skim though several of the articles...usually those that are university-based. Though even that's not a guarantee you'll get completely correct information. In other words, there's not even a 'best' website! :-)

You are so right that a great many plants can take quite a bit of chill. Even when I lived in coastal zone 8b, where frosts and freezes were common, many (so-called) houseplants were part of the permanent landscape.

Thanks for the book suggestion. As to the first poster, I did live in a subtropical area and we had tropical plants (crotons, oleandar, ti, coconut palms, citrus trees, etc, etc) that all lived in areas where our temperatures did fall to just above freezing some nights and our daytime temperatures at times were no higher than low 40's. They were all doing great down there and many were growing fine outdoors in zone 9 areas. In fact, most of the citrus growing areas in Florida are zone 9 and they do get some light frosts. So for books to tell me that citrus needs a minimum of 50 is just not true. Now it does need more light than I have in my sunroom. The only heating it gets is from a small vent and from sharing one wall with the main part of the house. It has a little over three walls of glass. We are in a deciduous forest and while the trees are providing little shade now, the skies are so consistently gloomy that I would not consider it bright at all.

It sounds like you don't have enough light for any of the plants you've mentioned, except for maybe the Ti. It would be worth it to invest in plant lights, perhaps.

OR, you could try some shade loving plants that can also take plenty of cold! I'm thinking of Fatsia japonica, Aspidistra elatior (cast iron plant), Aucuba japonica, Cyrtomium falcatum (holly fern) and such. All of these plants lend a 'tropical' personality to your interiorscaping, but are rather sturdy landscape specimens in semi-tropical to warmer temperate climates.

I'm sure that others can come up with even more suggestions.

I'm guessing that maybe the houseplants grown outside in cool temperatures are healthier because the rootballs are insulated in the ground, not above ground in a pot? Also because the outdoor plants probably get much more light in the summer than a houseplant, so they are more vigorous and healthy heading into the winter.

With both cold AND shade in your sunroom, you pretty much rule out most tropical plants that I can think of. But white bird of paradise and phildendron selloum probably would work, if you don't mind them getting a bit floppy and sprawly over time. And possibly clivia.

I do like the plants that rhizo suggested, they would probably work very well in your situation.

I've popped into this thread a couple of times, but was undecided (like Watergal) about whether you were talking about plants usually kept as houseplants that were growing in the ground, or if they were in your backyard in containers. After looking closer, I think I decided that you've moved from a USDA zone 10 area to VA zone 7; therefore, your plants ARE in containers. (I hope.) ;o) OH DUH! I just took note of the title of your post - 'Cold Sunroom'. Scheesch! Pay attention, Al!

Maybe we should look at the phraseology in your OP. One little 2-letter word can make a considerable difference between these two phrases: A) "... many of the plants they say can't survive less than 50 or 45 degrees growing in my backyard ..." verses the phrase B) "many of the plants they say can't survive at less than 50 or 45 degrees growing in my backyard ..."

'A'implies that any exposure to temperatures below 45-50* is likely to cause the death or maybe serious injury to the plant. 'B' carries with it that idea that exposure is more durative.

Serious injury or death of most houseplants under what is implied by 'A' is pretty unlikely. The conditions would have to be such that the temperatures would have had to fall swiftly (perhaps in a 24 hr period) from temperatures >about 80* to temperatures Now, in the case of 'B', I think they have a very solid case if their intent was to say that most houseplants cannot survive for durative periods at these low temperatures. The reason is because these lows inhibit photosynthesis to the extent that the plant is producing less energy than it is using. Whenever this is happening - the organism is moving toward collapse. If the trend is not reversed, the organism will die.

Someone who is not aware of the physiology involved could easily look at a plant subjected to these lows and conclude that the plant is doing fine at 45* and the book is wrong, but because there are no immediately observable symptoms of decline doesn't mean that all is well.

I think it's unlikely that you will find a book that gives recommended temperature ranges that are much different than the book you have in hand, but perhaps I'm wrong. It wouldn't be the first time. ;o) I hope what I offered DID carry with it the resonance of sound reasoning and is something you can use to help set aside your concerns.

Al