I’m wondering if you can propagate a lobelia from the leaves and flowers. Unfortunately, one of my plants in a container died because it was under-watered. But I do have the leaves and flowers from the other one. Could I start a new plant with the leaves or flowers?
It’s not clear from your question which lobelia you have, but the most common one used in containers is the blue or purple trailing lobelia (Lobelia erinus), which we treat as an annual plant here in Toronto.
Lobelias can be grown from seed but it is also possible to propagate them from cuttings. However, the cuttings that you use should be new growth, not stems that have produced flowers.
If you can find some new growth stems on your lobelia, choose a 4-5-inch stem, one with three or four nodes (these are the buds where the leaves emerge). Push the cuttings into a wet potting soil, leaving about half the stem above the soil. Place your cuttings in a protected shady place. Mist them a couple of times a day and keep them very moist.
The new plants will be ready when there is healthy foliage above the soil, and when the plant resists gentle tugging, which indicates that it has put down new roots.
Once you have some roots, you can transplant your plants into a new pot.
Good luck with your propagation!