If you want aggressive groundcovers that spread quickly - but don't invade or affect your larger plants - I have a few I like to use, which are common, easy to find and well-known: Ajuga reptans var. 'Bronze Beauty' - nice dark-leafed groundcover (a mottle of dark purple and olive green leaves) that is very shade-tolerant for the areas closest to the house. Short blue flower spikes in the spring. It will survive droughts but if there's water available it will grow very dense, to make it absolutely impossible for weed seeds to sprout from within it. But it's shallow-rooted so won't compete with your plants, nor will it shade them because it never grows more than 3 inches from the ground. It's easy to spread around by digging small bits that take well even in heat. Sedum spurium 'Red Carpet' - A very attractive red-leafed sedum that will really stand out in contrast to those varigated irises if planted right next to and among them. It is also very low-growing, drought-tolerant so it will not take water that could be going to your other plants, and this particular variety grows pretty slow. Sedum spurium 'Tricolor' - similar to 'Red carpet' but grows more quickly, has a green/white leaf that has a very visible pink blush over it when it's exposed to direct sun; it also turns more pink in the winter, and has pink flowers. Cerastium tomentosum ('Snow In Summer') - spreading silver-leafed ground cover that is also reliably less than 4 inches high, gets absolutely covered in white flowers in the early summer, and would pop against the ajuga and red-leafed sedum. It wouldn't contrast as well against the iris so I wouldn't plant it right there, but because it's the most drought-tolerant, I'd put it right up against the edge of the garden.

i think i have just been talked out of carex. have been wanting to try it in my bright wooded area but it sounds like they either may not perform well or look good in our hot climate or become hard to control (now those are two opposite ends of the spectrum!). alan, i have a plant someone gave me that looks a lot like the one in your photo, sort of like little spruce trees sprouting at the base of your carex. i believe it is a sedum. do you have that in a shaded area? mine is in half sun and is rather sparse. the one that my start came from is in full sun and very blue and dense.

Lschibley - the link below will take you to the Massachusetts Prohibited plant list. Most were banned on 1/1/06, but Berberis thunbergi (Japanese Barberry) is one of the plants being phased out over several years. Don't know if this includes cultivars but I would guess that it does. The phase-out allows nurseries and wholesalers to clear their stock over time without taking a huge hit. Other plants in this category include Norway maple, Burning bush, and Bush honeysuckle. I have all of these and more growing on my lot - like Ellen S I can see the highly invasive properties of these plants firsthand. Personally I would not plant anything on this list, including cultivars. Here is a link that might be useful: Mass Prohibited plant list

One thing to check out is speed of spread for the three plants. I don't grow either of the Carex you are interested in, but some Carex clumps or spreads slowly and some spreads fairly quickly. In my garden, Hakonechloa 'All Gold' makes a very slowly expanding clump so that it took probably 5 years to get from a one gallon pot to a two foot diameter clump. I like the bright gold to chartreuse range of colors it develops depending on the amount of sun it gets, and in my garden it is easy care.