Hello Keith,
Where are you located? My Buddleia does grow to 10+ ft. tall, but is not very dense. The stems also die down every winter. Right now the new growth is only 3 ft. tall max. I do not have Black Knight, but a friend and neighbor does. Hers does not grow as tall as mine nor is it dense. Her stems also die back every winter.

We live in Zone 6 - a microclimate in the middle of zone 5. This past winter the coldest temp. in our neighborhood was only -8F.

I had B. 'Locinch' that stayed at about 4 ft. That one lated for only 5 yrs. in my garden. It was the most fragrant Buddleia I could find. It was not dense either.

This post was edited by pitimpinai on Mon, Jun 23, 14 at 17:03

I grew 'Black Knight' Buddleia from seed via winter sowing back in 2009 and the next year planted out dozens of seedlings that have since grown to maturity. I have them in multiple garden beds, planted in both full and part sun. They're healthy and appear to be bothered by few pests. Flowering is abundant and the butterflies & other pollinators are on them constantly once they bloom.

So far none of mine have topped 10 ft. tall which may be related more to sun exposure and soil type than anything else.

Butterfly bush should be pruned back to 10" in spring each year (March where I am) since it blooms on new wood. Other than that it's completely maintenance-free.

You don't post your location or zone so be advised Buddleia is listed as invasive in some states due to its prolific reseeding.

Hi,

Thanks for the replies. Sorry for not listing more info....I am in PA....zone 6.

Keith