Height for borders while they mature

[MsAnnFrope]

I’ve replanted most of the borders in my garden. Mainly to get rid of the triffid like grasses.
I’ve got some plants which will take up substantial space when they mature eg eucalyptus, weigela, clematis but I really need some height in the mid borders to add some colour and shape while this happens. I’ve thought of verbena bonariensis but does anyone have any other suggestions?
I’m south facing and have clay soil which I’m gradually improving!

V. bonariensis would work, maybe build teepees for sweet peas, there are still some in garden centres. Possibly foxgloves, although they like shade but I've grown them in full sun too. Knautias are tall and airy. Echinaceas will love the sun and they cope well on our clay. It really depends on what you like. The Crocus website is good for ideas and gives clear plant heights.

Thanks @Janedownourlane I've got some sweet peas I've grown from seed and some cosmos to put in.
have you ordered plants from Crocus? Apart from David Austin I've not really bought plants online but our local nurseries are struggling to keep up with demand.

Yes I have bought from Crocus and have always been pleased with the quality of the plants but they are pricey. I've also noticed that they say 'out of stock' a lot at the moment.
I've just remembered that we put in a lot of Cosmos Purity and Nicotiana Alata when we'd just done some work on our garden and they grew huge on the clay. I think clay is often thought to be a problem but improved clay is really fertile and we've noticed that everything grows taller than we expect!

Ammi magus is nice in with the verbena.

Agree with pp above.

For tall perennials I’d also suggest plume poppy (Macleaya), Eupatorium Riesenschirm, Helianthus Lemon Queen, Filipendula rubra Venusta.

Annual sunflowers?

They are great suggestions thanks @Trethew and some at least are available on Claire Austin