Hello! I’m just north of Guelph in zone 5b, with nice loam soil.
My question is about dahlias. I’m growing two types of dinnerplate dahlias, Thomas Edison and Otto’s Thrill, and I’m having severe problems with daytime droop when they’re in full sun. They are currently planted and staked in the garden in the front of my SW-facing, yellow-brick house (I planted them before realizing they don’t tolerate sun as well as other varieties). They get the harshest sun from about 10am-2pm, then some reprieve from the shade of a neighbouring tree until about 5pm before getting some evening sun. They’re mulched (and I’m dealing with the earwigs as a result), and I’m regularly & deeply watering them. They are flourishing and look quite healthy aside from the several-hour-long period of droop every day.
A couple things to mention – one of my Thomas Edisons is potted, and the same daytime droop happens with it as the ones planted in the garden. I’ve since moved that one to the NE side of my house and it’s doing quite well with the morning sun. For the dahlias in the garden on the SW side, the bricks don’t seem to give off a ton of heat even in this heat wave, so I don’t think that’s a factor. Also only the dinnerplates droop — I have a couple smaller varieties and the sun/heat doesn’t seem to bother them.
Could you provide any advice for protection? Or any advice in general? I don’t want to lose these plants or stunt their growth. I’ve been told to use umbrellas but I can’t see that being a long-term solution in my front yard. If I’m looking at shade cloth, can you point me in the right direction there, or recommend anywhere that I can buy it locally? I’m not even sure how I’d go about setting it up along the front of my house. I would be so grateful for any suggestions. Thank you!
It looks at though you are doing everything right. The midday droop in your dahlias is the plants’ way of protecting themselves against the heat. Cleverly, the plant diverts water from its stems and leaves to its roots as protection against stress. As your plants revive once the sun sets, it is unlikely that you have a more serious problem such as verticillium wilt.
Although you can try and prevent the daily drooping by opening an umbrella, putting up shade cloth or other protection against the intense afternoon sun; this should not be necessary provided you keep ground moist. If you do want to go this root, shade cloth should be available online or at your local garden centres.
Here are links to an informative article on watering by Dalhia University published by the American Dahlia Society: https://dahlia.org/wp-content/uploads/2018/02/watering.pdf
as well as a previous Toronto Master Gardener enquiry relating to drooping dahlias: https://www.torontomastergardeners.ca/askagardener/dahlia-with-drooping-leaves/
Note that there is no long term harmful effect from this daily wilting. In future years you can either plant these varieties where they only get morning sun; or in containers which you can move out of the sun during the warmest part of very hot days.