I have a beautiful trumpet vine which grows against a south-facing fence. It flowered for the first time this year. Several sources say to prune it in March. Is that correct, and if so, how close to the ground should it be pruned? Also, I’d like to plant a few to climb my pergola. Should they be planted in the ground or would large pots be OK?
Your sources are correct, although my research indicated that ‘late winter to early spring’ is fine for pruning Campsis radicans. Whenever you prune, you want to consider that frost (or even cold weather and/or wind) can damage new growth–March is generally considered a safe time from that perspective.
Trumpet vine flowers on growth produced during the current season, so you can cut it back hard if you are trying to control its growth. Pruning it to within 6-8 inches of the ground (when it’s young or if it needs a renovation later on) will encourage vigorous growth of a stout, strong set of basal branches.
The American Horticultural Society’s Pruning and Training (DK Publishing, 1996), says the following:
- Select two or three of the strongest shoots and remove the rest.
- Train [them] to the supporting wires or trellis (…) until shoots extend fully over the allotted space (…) it may take two or three seasons to complete the framework (…)
- Once it is established, prune the plant annually, spur-pruning all lateral shoots back to within two or three buds of the main stems.
If you prune it to the ground next year, you can begin to develop a strong framework, if you haven’t already. Otherwise, you can prune as needed to the suggested two or three buds from the main stem. You can also follow this set of instructions if you choose to do a renovation. Over time, this vigorous plant may outgrow its space; you can then cut it to the ground and let it come back. It responds well to hard pruning.
I did not see mention of this plant in any of several books I consulted about container gardening. While that does not mean you cannot grow this vine in a pot, my suspicion is that the stout base required of this vigorous grower may not develop in a pot. This plant does need sufficient room for a root system that can support the base and each season’s growth. If possible, I think you should plant the vines in the ground.