Ground Cover question

[ll777]

Hi,
I have some ground covers, mostly various tymes like Wooley thyme, growing on a slope i have in my back yard.
There seems to be weeds growing through them! If I put bark/mulch around the plant (they aren't too big yet about 2ft x 2ft) by lifting the trailing parts and finding where its rooted - will I prevent it from spreading or will it grow right over the bark/mulch? Wasn't sure if it just spreads or needs to grow up and spread too? If that make sense. So basically if I planted a 5in planter and it's grown to 2ft by 2ft - it seems by lifting the trailing parts that it's still only 5 inch but has spread by 2ft x 2ft or is it actually getting a bigger base as well? And either way does mulching by the base prevent it from spreading?


Any responses would be great!!!

[Newt*]

You can and should put down a layer of mulch. Unless you cover the base of the plant they will grow over the mulch. Do not put the mulch against the base of the plant but allow for air circulation and expansion. This is a different plant, but the picture should explain it.
http://uktv.co.uk/images/standarditem/L1/500058_L1.gif

You can see a similar ground cover here and it is growing over the mulch.
http://www.hotgardens.net/groundcover_Crassulacae.JPG

This mulch with liriope is a bit too close to many of the plants and can cause the base to rot in wet weather.
http://www.louisvilleky.gov/NR/rdonlyres/807AFE34-6D16-4D61-8A1D-E883D587B8D2/0/Liriope4Mulched.jpg

Newt