Advertised 'height and spread'

Dirty Harry

Does anyone know of any sites that accurately list these figures for plants?

I'm making a new border this year so trying to plan what goes where but the inaccuracy of a lot of these doesn't make it easy.

A quick example would be the erysimum Bowles' Mauve I have-

https://www.gardenersworld.com/plants/erysimum-bicolor-bowless-mauve/

Height and spread listed as 45cm x 50cm. The actual plant I have is more like 1.2m x 1.2m.

B3

A lot depends on your growing conditions

Dirty Harry

Yes I'd figured that would play a part but I'd have still hoped for things to be in a rough ballpark rather than potentially so far out.

Is the best way to plan a border to ensure enough room is given then re-assess after a year or two?

edhelka

I usually check a couple of websites to see the range of sizes or the average. It can't be precise because the same plant can grow very differently for different people.

amancalledgeorge

I think the RHS website is quite accurate but measurements are not a patch to actually having some growing experience in situ. For the ubiquitous Bowles Mauve you mentioned they go with a 0.5 to 1m in height and spread which is a fair representation of the plant, depending on its cultivation conditions. Any site that pretended to be more accurate it would probably be just a guess and I wouldn't trust it. 

Dirty Harry

Mmm if you've found the RHS site to be generally accurate I might use that as my guide and go by the larger numbers.

LG_

I would go with the RHS site too. 
Two things to note - as well as the eventual height and spread range in the box, they also often give species / cultivar specific height in the description box (eg: https://www.rhs.org.uk/Plants/12705/i-Phlomis-russeliana-i/Details). Also note the 'time to ultimate height' - if it's several years then you probably don't want to leave all that space bare for ages, but instead go for shorter-lived plants nearby while it grows and / or plan to remove or rethink things as time goes on. 

Dirty Harry

Yes good shout, foxgloves can come into their own then as well as gap fillers.

fidgetbones

Planning a new border, I put the plants in that are going to fill it at the required spacing, then fill the gaps in between with short lived plants. I used buddlejas and lavatera to fill a shrub border alternating between the slower growing, more expensive, longer lived ones. As the  magnolias etc got bigger, I took out the lavateras and buddlejas.  In a herbaceous border, in shade use foxgloves to fill gaps, in sun use cosmos and nicotiana.