How do I prune Verbena bonariensis?

Question

In my region, Verbena bonariensis is a perennial rather than an annual. It's getting quite tall, with some close to 8 feet even though it's not supposed to top 6 feet, and in the wind has taken a battering so that I've had to stake some of the bushes which were blown over.

I've read that it should be cut back after it's flowered, and some of mine are getting like that now, though I'm unsure if that applies to regions only where it grows as a perennial.

I've got flowers looking like this in their second year:

enter link description here

And others looking like they're forming seeds:

forming seeds

and close up:

seeds close up

This is one example of the effect of wind:

wind swept Verbena

This is the base of this same leaning plant:

Verbena base

So, now it's going to seed, should I chop it back to the ground and wait for others to come up from self propagated seed? Or, cut it back some inches off the ground, and at what stage?

Oh, and I've given up trying to manage the powdery mildew that affects these plants in only one half of the garden.

I'm at 150 m above sea level, and in mid summer right now though today it's wet and windy. Winter rarely gets below freezing here.

Am I the only one that chuckles when reading the name of this plant? I'm so immature, — Brenn, Jan 14 '17 at 05:19
@Brenn - its because you're a bloke you find it funny, probably, or maybe the way you're pronouncing the name in your head. Its never occurred to me, I say, phonetically, "bon-ar'eensis" — Bamboo, Jan 14 '17 at 12:36
@Brenn - well, we all need something to make us smile these days;-) — Bamboo, Jan 15 '17 at 09:32

Bamboo · Accepted Answer · 2017-01-14T12:52:10.110

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I'm having to think hard about this because you're in the other hemisphere from me! Right, so it must be summer heading into autumn where you are, and your pictured plant doesn't appear to have been cut back at any time. What I usually do with these in the UK, when it gets past mid summer, is just cut off the stems which have flowered, or been broken or are diseased, back to the mainstem to encourage more flowering, then reduce the whole plant by half or two thirds in late autumn. I leave that in place till the following spring, then cut down to around 2 inches to encourage new, bushy and healthy growth. I think your winters are a little warmer than ours in the UK, so if you think they'll make it through winter if you cut down to 2 inches in autumn, do it then.

Usually, if you're not too attentive to deadheading, they seed themselves all over the place, but it looks like yours isn't growing somewhere where any seed that falls will be able to germinate, so if you want more, you should maybe try to collect seed, which means leaving some of the flowerheads to mature before cutting down.

edited Jan 14 '17 at 12:52

answered Jan 14 '17 at 12:35

Bamboo

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Sounds good. Reduce all stems to 2 inches off ground in autumn, and save any seed for propagation. – Graham Chiu Jan 14 '17 at 18:38
Most of the ones I cut back have not come back again! – Graham Chiu Nov 17 '17 at 19:17
Shame - obviously your winters are not much better than ours then, and here, I leave the cutting back to a couple of inches till spring, I don't do that in autumn, as described in the answer. – Bamboo Nov 17 '17 at 20:22
It has seeded everywhere even if it didn't survive the cut back. – Graham Chiu Jan 31 '21 at 21:45

score 1 · Answer 2 · answered Sep 17 '19 at 23:57

I think I'm late with the answer but it will serve future readers. :)

I strongly agree with the previous answer, both in pruning to encourage the flowering of your verbena (in mid-summer) and pruning to encourage development (in spring).

On the other hand add that you can cut at the base those stems that have become too old, woody and no longer develop strong shoots. Perform this task at the beginning of spring at the moment that begins to generate new shoots, if possible look for if from the base of these old branches some sprout is emerging and cut on top of it.

The beginning of spring is also good to eliminate small shoots that leave the base and seek to propagate the plant. Verbena Bonaerensis can become very invasive if you don't control it.

Well that would be all to complement the previous answer. Regards!! :)

score 1 · Answer 3 · answered Feb 26 '20 at 21:48

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I leave my Verbeana flower heads on until Spring, then cut back. The winter song birds love the seeds from the dead, brown flower heads & those seeds help the native song birds survive the cold winters.

answered Feb 26 '20 at 21:48

Northern most U.S. state -

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How do I prune Verbena bonariensis?

3 Answers3