Actually Larkspur lasts well into July here for me in zone 6 and re-seeds well coming up in late summer-fall to winter over. I also like re-seeding Sweet Alyssum as fillers which last clean up until the first hard frost; does well in moderately dry hot sun. A light sheering all around when most flowers are fading and they will repeat bloom and get mounds get bigger and fuller each sheering. Snapdragon (mostly perennial for me) but also re-seeds and is a great filler. Other great annual fillers I like are: *Statice sinuata (dwarf types....does sometimes reseed) *Scabiosa atropurpurea....awesome cut flower blooming mid June thru frost *Nigella...flowers spring, interesting seed heads, good re-seeder *Profusion Zinnia The Vinca Karen is referring to is Catharanthus roseus...Madagascar Vinca/Periwinkle. Blooms late from seed, so needs to be started early or purchased.

Spraying poplar suckers has potential to damage the parent tree. Fine mulch is ideal for getting lots of new little plants coming up, as mentioned. Paper mulch is best for smothering weeds in an area that is going to be made into a bed later, rather than as a routine maintenance tool. You put down a thick layer and get it wet, keep it wet. Also a decorative mulch may be put over the newspaper layer, if desired. Coarser mulch such as clean arborist wood chips or purchased play chips is the most effective, however as has been pointed out in response to one of my posts on this site there can be issues with smothering when such materials are used near herbaceous plants. Even when applied some distance back chips may often migrate and get on top of perennials. Really if you are going to have flower plantings of much size and scope you can expect to be out there hand weeding etc. as a matter of course. If working among your flowers like this is more a vexation than a relaxation then consider making some changes. One way to include herbaceous plants in a home landscape without the upkeep being too much is to have one small or smallish area where these are planted, with the rest in lawn and woody plants (mulched with wood chips). This post was edited by bboy on Mon, Aug 18, 14 at 15:14

Thanks for the reply. It's a very large mature mixed border and there's not a lot of space left for new perennials. It's also on a fairly steep slope so I have to be careful to plant things that don't typically flop. I learned through trial and error over the years what grows well with minimal maintenance and looks good throughout the growing season. There is already some early season color from knockout roses, heuchera, variegated iris amd May Night salvia and some sprirea. I use some self seeding annuals, particularly cosmos, to carry color through most of the growing season. I,m looking ahead to a graduation party I'll be hosting in early June next year and had the idea that there may be some earlier blooming annuals that can be sown from seed this fall to add a splash of color at that time.

I love blue salvia and I use it a lot, and it often comes back the next year (behaves as a perennial). So you want a low-growing, non-invasive, non-yellow or red perennial to go in front of your salvias? Sweet alyssum, although it is technically an annual, very often reseeds itself. I'd use white, although it comes in pink too. My blue salvias (usually Victoria Blue) grow more like 2 feet tall. I use daylilies, which are very well-behaved and come in a large variety of colors -- you could find some of the shorter varieties, and they would also work behind or among your salvia. There are pretty artemisias that are low-growing with silvery foliage. If you want to do herbs, you might think about lavender -- some of them have silver or white flowers rather than the traditional lavender color, and the foliage is usually a silvery blue color. Other silvery herbs would be curry plant or one of the many other sages (of course relatives of your salvia). You might consider ajuga, which is a low-growing ground-cover with bronzey-green foliage and pretty blue blooms. I don't know where in Maryland you live, but I lived on the Eastern Shore for many years and have grown all of the above successfully. I'm not a big white coneflower fan -- the ones I've seen have not been a clear white but sort of a muddy color. Another annual that often behaves as a perennial in our area is snapdragon. They are very easy, not demanding or invasive, and come in just about every color you can imagine. Many varieties of varying heights. I have some really pretty pink ones that are only about 8" high, and they overwintered from last year and are now in full bloom. The great thing about blue salvia is that they look good with almost anything you can think of, since their color is a pure blue -- not purplish.