birdsnesthead, I was hoping that someone in your zone would respond, as I don't know what happens to Physocarpus in zone 5. Here they do not die back at all. A few thoughts - Lemon Candy is advertised as smaller than 'Darts Gold'. However, recent introductions that have not been tested extensively in the landscape do not always perform as stated, and many of the so-called 'dwarf' or smaller introductions get much larger than the claim, it just takes longer! Lemon Candy is a Ball Hort introduction and I am currently suffering through another of their exclusives (Photinia Fireball Red) that they advertise as 4' tall and it's headed to 7'!

Another thing about Physocarpus - the common name is ninebark for a reason - the bark is amazing. So, while you could keep 'Darts Gold' small by coppicing every couple of years, you'll miss out on a major attraction of the shrub. I like to prune them to small multi-trunked trees, which takes several years, but provides wonderful winter interest when they are leafless.

I'm not helping you much as I'm just adding other issues to your wish to get the one that holds its color best through summer! But just wanted you to factor in those considerations as well. Maybe someone in your zone will have experience with Lemon Candy's color retention and growth rate. (btw here 'Darts Gold' holds its color all summer but that may well not be relevant to what you would experience in 5)

I've had a Ninebark, Physocarpus opulifolius, 'Diabolo', for two years. The deer nibble on it a bit. Looks like I'll have to move it to a less deer traveled area in the garden.
Mike

Little closer, zone-wise. I have Ninebark "Dart's Gold", but I do think "Lemon Candy" might be yellower given all the right circumstances.

Dart's is yellow/chartreuse enough for me - on the order of some old unknown variety of Mock Orange I also have. I have enough space that I don't need to prune for size, etc. If that were the case, I wouldn't have made the purchase - I like the arching branch habit and don't want to sacrifice that and the copious blooming to make it fit somewhere. The shredding, multicolored bark is phenomenal - think it took maybe 5 years for that to really start.

Just checked with another nursery, they have a variety called "Amber Jubilee", but I think I still want "Lemon Candy". Now if it would go on sale!