Q. Most of the Sedum spurium in my Seattle garden is thriving and blooming. But in a few places it looks straggly and weak. Should I cut it all back or just prune the bad patches?
A. Pruning will strengthen weak sedums if all that is wrong is neglect. And thriving plants can be left alone. But you will get the most uniform carpet if you remove old growth from all the plants. Wait until flowering is finished, and then clip away everything except healthy stems rising directly from the soil.
Sedums need good drainage to prosper, so if the weak ones are in soggy soil no amount of pruning will help. And some S. spurium varieties are simply less vigorous than others. The variegated green, white and pink Tricolor and the red-leafed Red Carpet, for instance, are on the delicate side.
Dragon's Blood, which has green leaves and red flowers, is dependably robust and so widely planted it is almost synonymous with S. spurium. But if you'd prefer a tight mat of bluish green dotted with pink flowers, the one to plant is John Creech.
Growing 'Baby' Onions
Q. We really enjoyed the creamed baby onions we had at Thanksgiving and would like to grow our own. It seems as if it would be easy, but is it?
A. Pearl (a k a boiler) onions are baby size, but that is because they are stressed by crowding, not because they are young.
Almost all onions will produce dwarf bulbs if you space the plants closely enough, but there is more to a good boiler than smallness. If you want tasty, uniform pearls with thin skins that are easy to peel, it is best to plant boiler varieties, which thrive close together.
The choices are many, including reds, which turn pink when cooked, and flat, golden cipollini, but the best choices for cream saucing are old white standards like Barletta and the heirloom Paris Silverskin. All are quite easy to grow, as long as you are fond of weeding.
Address questions by e-mail to email@example.com. Unpublished questions cannot be answered individually.