To this point, I have successfully overwintered a mandevilla. It was pruned back to encourage a denser plant and additional branches. My question is when do I start fertilizing, the frequency, and strength?
Starting in February, it is recommended the plant be pruned back well and fertilized once a month. During spring and summer, while it is actively growing (i.e., beginning when you see a flush of new growth), fertilize with a liquid high-phosphorus product, e.g., 10-20-10 every 2 weeks. Repot the vine and put it outside once all danger of frost has passed. Be sure to harden off the plant to get it use to the high uv of the sun, so introduce it gradually. Mandevilla bloom time tells you how to do this. Wear gloves when pruning as many members of this plant family have a milky sap that can be irritating.
We have several Q&A concerning mandevilla care posted on our website. For example, see Overwintering mandevillas, which also includes a couple of useful links to other postings. It’s easy to find previous Q&A on the website – just go to the Toronto Master Gardeners home page and enter the search term (e.g., “mandevilla”) in the search box under “Find it here”, on the right of the page. Happy reading!
Clemson Cooperative Extension’s Mandevilla provides further detailed information about how to grow the plant.