I moved my plant to a bigger pot and now the leaves are falling off. What can I do?

In February I was given a jacaranda tree/plant. Initially it did well and sprouted new leaves. About two months ago I repotted it into a bigger pot and since then its bottom leaves have started to droop and eventually they fall off. I have tried keeping it in a sunny spot and in a shady one but it never looks happy. Any advice on helping it adapt to its environment? – Emer Sheahan, Co Dublin
The jacaranda or fern tree (Jacaranda mimisifolia), a tropical species that’s often seen growing as a large ornamental tree in warm parts of the world, is prized for its brilliant display of trumpet-shaped, lavender-purple flowers, which appear in mid-to-late spring on bare branches. But in Ireland, where temperatures are much cooler, it’s instead usually grown as a frost-tender, fast-growing plant that needs a very sheltered, warm spot in full sun and does best in a bright conservatory or glasshouse.
A very free-draining compost leavened with plenty of horticultural grit is essential, and should be allowed to almost dry out between waterings. A liquid feed every two to three weeks during the growing season will also help to keep it happy.
The variety best suited to container growing is the compact jacaranda ‘Bonsai Blue’, which reaches a height and spread of two metres.
Judging from your description, I would think that your plant’s root-ball is sitting in cool, damp compost, which it would certainly resent. Repotting it into a larger pot would have aggravated the problem if (a) you didn’t use a gritty mix as described above and/or (b) the new pot size was considerably larger than the original. Known as “bumping up” or “up-potting”, the process of transplanting a plant into a larger container can cause transplant shock, particularly if the difference in size between the two containers is too much. The latter results in the root-ball being surrounded by so much fresh compost that the plant struggles to re-establish itself, especially if it’s being overwatered. A variety of soil-based diseases can then occur, resulting in the plant dropping its leaves and sometimes even dying.
All of the above aside, the Irish winter is far too wet and cold for jacaranda to survive outdoors (it needs a minimum of five degrees) so if you’re growing yours outside in a pot, then you’ll need to bring it indoors in the coming weeks.
This is where things get even trickier. Jacarandas do not make good houseplants as they quickly get leggy and weak in the warmth and low natural light conditions typical of Irish homes from autumn to late spring. Instead your plant needs a bright, cool but frost-free spot in a glasshouse or conservatory (again, where temperatures don’t drop below five degrees).
It also needs very minimal watering, only when the compost has completely dried out and then only in very small amounts. It will naturally drop its pretty, fern-shaped leaves at this stage as it goes into winter dormancy but will produce fresh foliage the following spring.
Is it worth all the faff? That’s for you to decide. But perhaps the moral of this story is for us gardeners to beware of well-meaning friends bearing gifts.