I have two questions, both about container gardening in Toronto.
1. Suggestions for a perennial climbing vine for a third floor hot deck (with a watering system)
1a) is there a hardy clematis that might survive the winter?
2. Suggestions for perennial grasses that would work in containers on the same deck.
It’s heartening to see more and more “sky” gardeners wanting green things on their balconies and decks. Even so, it’s not quite the same as gardening on the ground. Exposure is harsher including heat from the sun, especially on south and west facing balconies, and the wind is usually greater further up towards the sky. This means that dessication is an issue. Also, being on a balcony, lighter pots and soil are a must, as are foolproof ways to keep water from dribbling to your downstairs neighbours!
With a watering system, I think you have the dessication and perhaps the water dribbling issues covered. However, you describe your deck as ‘hot’. A further way to mitigate heat, if you haven’t already done this, is to raise the pots on ‘feet’, which are available at most garden centres, or placing pots on a raised open construction platform. This allows better air circulation, so heat is not coming up from the deck and drying your soil from underneath. This also has the advantage of keeping sow bugs or pill bugs from congregating under the pot, which is more of an issue on the ground but sometimes they come with the plants and multiply. They mostly eat dead plant material and are harmless but a whole group of them when you move a pot can be a bit startling.
So, plant material for a hot deck with a watering system.
To address your question about clematis. Although all clematis worship the sun, they hate having hot roots. In the ground it is easily mitigated with surround plantings of perennials in order to shade the roots. On a deck and in a container, this is a bit more difficult to do as the whole pot surrounding the roots heats it up. I have found one clematis that has been bred for pots and may be suitable. It’s called Climador or ‘Konigskind’. It stays relatively short, has blue/purple flowers and is suitable down to zone 3. It reportedly can survive in a pot over the winter with some protection. Even so, in such an exposed area, the clematis may not survive our winter freezes with high cold winds.
I suggest that a vine, perennial in more tropical climes, but annual here, would be a better bet. Some, if the pot is not too big, can overwinter indoors until next year if you have a suitable window. Many are now available at garden centres and are already potted and staked to provide instant colour. The black-eyed Susan vine (Thunbergia alata), with orange, yellow or white flowers will bloom all summer and would do well. A mandevilla vine, a tropical with deep green leathery leaves and huge flowers in pinks to reds that blooms all summer, would be another option. Both can be overwintered indoors.
For further information on suitable vines for a balcony see the link below:
As for grasses, most ornamental grasses are quite drought tolerant, once established. Most prefer well drained soil. I am going to assume that grasses of a half metre to a metre would be best for your balcony. Some grasses grow to 3 metres and may not be what you want. The Eragrostis grasses or lovegrasses grow less than a metre and are excellent specimen plants. Their flower heads are like plumes and depending on species, come in tan to purplish in colour. The northern sea oats (Chasmanthium latifolium) have flat green spikelets on slender stems (they look like an oat flower), dangle in the breeze and turn reddish brown in the winter. The Avalanche feather reed grass (Calamagrostis x acutiflora ‘Avalanche’) grows to a metre, is variegated with a white stripe, and is narrow in habit. The white flowerheads show up in summer, turn pink as the weather cools in fall, and then tan for the winter. With winter protection, they may come back in the spring.
For more information regarding balcony gardening: https://www.canadianliving.com/home-and-garden/gardening/article/7-secrets-to-successful-container-gardening