My mandevilla has lots of yellow leaves falling. It has green leaves on the outside.
What should I do (fertilise) ? I am planning to take it outside soon.
It has a few flowers. What should I fertilize it with?
Thank you for contacting the Toronto Master Gardeners about your Mandevilla.
Some basic information about the mandevilla from the Missouri Botanical Garden:
Winter hardy in the southern United States, this plant is usually grown in large containers that are overwintered indoors. When growing as a vine, small trellises (to 3’ tall) are usually inserted in the containers for the plants to grow upon. Bring plants indoors in fall before frost and overwinter them in a warm, sunny room. Prune plant stems back before placing them outside in spring after last frost date. Best with a moist, well-drained potting soil in full sun to part shade. Appreciates some part afternoon shade in hot summers. Pinch to promote shrubby growth.
As noted in a previous published response to a Mandevilla: 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 diluted 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. Last frost date for Toronto is May 11. Be sure to harden off the plant to get it use to the high uv of the sun, so introduce it gradually to the outdoors. Wear gloves when pruning as many members of this plant family have a milky sap that can be irritating.
It sounds like yellowing leaves could be that the plant is compensating for lower light levels indoors and loosing leaves it no longer needs. Also check that the plant is evenly moist in well-drained soil and that you are not overwatering. If you prune back the plant now, prior to putting it outdoors for the season, it will fill out nicely.
As noted in another published response: When you do move it outdoors, move your plant to a partially shaded location, or an area with morning sun, and carefully monitor the soil moisture level. Do not allow the soil to dry out, but make sure it is not too soggy. The plant pot must have drainage holes, and these must be properly functioning.
We have several Q&A concerning Mandevilla care posted on our website. 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.
Clemson Cooperative Extension’s Mandevilla provides further detailed information about how to grow the plant.
Happy gardening with your Mandevilla.