Conservatory plants
This is one of a new series of posts based on real questions I have been asked. Feel free to add to the answers or include your ideas and experiences.
Someone asked for recommendations for plants in an unheated conservatory. They had some cacti and an aloe but wanted something ‘leafy’. They had discovered that Dracaena marginata and orchids would not survive.
An unheated conservatory is a tricky place to grow plants because it is often too hot for plants (and people) in summer and then it can be icy cold in winter. If there is any heat then if it is connected to the central heating then it can be turned off at night. This restricts the range of plants that will survive let alone thrive. I would suggest a strelitzia (bird of paradise) which will survive extreme heat in summer and temperatures down to 0c in winter if kept quite dry. I remember one that once got too big and was eventually put in an unheated polytunnel. It rooted into the soil so could not be moved and was left out for years and, though it was not a thing of great beauty it flowered like crazy.
Other options are Cycas revoluta, which is palm-like and very tough and Phoenix canariensis which is hardy in some areas. Both will put up with extreme heat in summer as long as they are watered and tolerate low temperatures in winter if more or less dry. Oleanders (Nerium) should also cope but be aware that they are poisonous if eaten. Red spider mite is going to be a possible problem.
Orchids are a varied bunch and cymbidiums may put up with the winter cold but should be put outside in summer because they will not like the extreme heat. Making cultivation more complex, pleione orchids would be OK in winter and will bloom in spring but would not tolerate the heat in summer, and will need to be outside as soon as temperatures start to rise.
Many conservatories are put on south walls and these become ovens in summer. Any other situation is an improvement. A solid or insulated roof will make the structure better for plants and people.
The Biking Gardener 
Phoenix canariensis gets huge! It is the biggest of the common species within the genus. Phoenix roebelenii is much smaller, and seems to be the smallest of the common species within the genus; but I do not know how much chill it will tolerate. It lives outside here, but this is a relatively mild climate. Phoenix have spines at the bases of their fronds. Those of Phoenix roebelenii are rather bothersome, but those of large species can be downright dangerous! Cymbidium orchids actually appreciate a bit of mild chill in autumn, although shorter photoperiod may be enough to convince some of the change of season. (It seems to me that floral shoots begin to develop even prior to chill, and just grow very slowly through winter.) I really do not know how much chill they can tolerate beyond ‘mild’ chill.
I know that Phoenix canariensis is potentially a huge plant and that P. roebelinii is a more atractive pot plant but the Canary date palm is frequently sold here as small plants, often for less than 20 euro and is the most commonly available palm. It is often sold as a hardy palm but only survives in the mildest areas and even there rarely forms a real trunk.
Nurserymen should be more responsible! There are a few palms that they could grow for your region. Sabal minor is not an impressive palm, since it does not develop a trunk, but for the same reason, works nicely as a potted plant. Phoenix canariensis used to be one of the three most common palms here, but new specimens are somewhat uncommon now that garden space is so minimal around the majority of modern homes. During the Victorian period, when they were a fad, they were more popular as big foliar plants than trees, since they took many years to develop trunks. Many that are big trees now were planted as such back then. They sit at ground level for many years until their trunks are wide enough to launch as trees.
Here, the phoenix are grown, I assume cheaply, in southern Europe and shipped over. As you say they take ages thickening up at the base before they launch themselves into a trunk. I have the three hardiest palms in the garden: Chamaerops, Trachycarpus and Butia and the latter is finally starting to settle and make some growth. They are all slow, which is why Cordyline australis is so popular here.
Oh, I did not consider Butia. I am surprised by how resilient Cordyline australis is to chill. It is available in the Pacific Northwest. I was annoyed to see it there, but have since learned that it performs nicely.
I remember wrapping cordylines in winter to protect them but it seems unnecessary now. They do well here although a cold winter will knock them back and they sprout from the base. people dislike them because of the falling dead leaves but they are nothing compared to ‘proper’ palm leaves dropping off!
Old garden manuals suggest cutting them down as they grow into trees, so that they can grow as foliar plants, rather than sculptural plants. I still like the old fashioned sort as small trees, particularly on the coast. They were popular in San Francisco a century ago. Modern sorts do not get as big, but are neater and more colorful. Most palms that are popular here do not drop their leaves, so must be groomed. Without grooming, some become hazardously combustible. Also, Mexican fan palms can drop entire beards of accumulated fronds, which is very dangerous!
Yes the thought of great palm fronds dropping down from on high is scary. Grooming palms must be a terrifying job.
It amazes me that palms are as popular as they are, although I am pleased that they are, since they are so appealing in some landscapes. Mexican fan palms grow so tall that a single frond can dent a car. Beard collapse generally happens lower down, but can crush a car. Grooming palms is not such a bad job for those who enjoy doing it. In southern California, some arborists specialize in palms, and some specialize in particular palms, while other arborists work on trees that are not palms. Unfortunately though, beard removal is still one of the most dangerous arboricultural jobs. Although rare, beard collapse has killed a few arborists.
We love palms in NW Europe, mainly because they are on the borderline of being growable – and they look so exotic and almost kid us in to believing it is warmer than it is
I notice them more in pictures. To me, they look odd in some places, such as Switzerland. But of course, that is part of the allure.
You know, Mediterranean fan palm might be happy in a conservatory as well, and windmill palm should have no problem with it, although, since both live outside there, so there is no need to keep them inside through winter. Windmill palm lives in New England and the Pacific Northwest.
A strelitzia does well in the unheated glasshouse overwinter here and is put out in summer. Flowers well.