Why such a difference?

Hi again everyone,

A very simple question I hope. I’m looking at getting a Amelanchier Lamarckii. When I look at eventual height/spread on the rhs website it says 4m/2.5m - Perfect! but on the gardeners world site it says 10m/6m - not so perfect.

A rather big difference….

 

Welcome to the funny world of gardening. Some places always seem to under state eventual heights in order not to scare the customer but the main reason are cultivars can grow to different sizes, sometimes plants are grafted and even the way they are grown, as in soil conditions or multistem, can affect height.
In terms of amelanchier then multistem tend to stay smaller and a lot of places quote for a ten year height and spread. If you have a single trunk and it's a wild type species, then they can be big trees if given enough time. In my area, even the very old amelanchier lamarckii seem to be on the smaller side you have quoted.

 

So much depends on: soil, aspect, competing plants and the climate where you are.

 

I see, thanks. Some of the numbers were scaring me slightly. I’m looking for multi stem varieties so hopefully they’ll be on the smaller side.

 

Often the height or size is stated after a specific number of years, I don't think any tree actually stops growing until its in decline.
It's always got to be an estimation.

 

Yes most guides quote height and spread after 10 years, to indicate the rate of growth under "good" conditions. Some do quote ultimate dimensions but as already said it can only be an estimate.

 

I would probably trust the RHS rather than the GW site. As said growing conditions will affect size but also genetics especially where plants are not clones of the parent. Plants like people vary.

As a rule of thumb, I’ve read that multi-stems tend to be towards the smaller end of the range. Whether that is based on evidence or anecdote I couldn’t be sure

 

There’s a small columnar variety that grows to around the dimensions you are looking for @machtucker called Amelanchier Obelisk. It’s a neat tree, I planted one last year to fill a gap to hide my neighbour’s garage. It’s also available as a multi stemmed tree. (The RHS site gives different dimensions!)

Amelanchier alnifolia 'Obelisk' Tree

 

I have a multistem Amelanchier Canadensis, which is not meant to be that different to Lamarckii. I have found it to be very slow growing and rather underwhelming in general. Considering they take pruning well, I don't think I would be overly concerned about the max theoretical size.