Q: I want to expand a bed of ground cover this spring. Right now, the area is grass. Should I plant into the grass and then mulch around the plugs of liriope I’m going to plant? Or should I kill the grass first and, if so, how and when? Should I use an herbicide?
A: You can begin now by covering the turf with 3 to 4 layers of newspapers, topped with 1 to 2 inches of compost, and then covered with 1 inch of mulch. This will smother and kill the grass, plus any weeds in the grass, and they will both probably decompose by the time the soil is dry enough to plant your liriope in spring.
It's also possible to kill the grass and weeds with a total vegetation killer herbicide containing glyphosate, but you'd have to wait until the grass and weeds were actively growing so they could absorb the herbicide. The newspaper and mulch method is the simpliest and cheapest. See our online publication on ground covers at www.hgic.umd.edu.
Q: How do I overwinter geraniums so that they produce flowers the next summer? I keep them on a cool sun porch in winter and the leaves look great, but last summer I got almost no flowers.
A: The cool porch is good for geraniums (strictly speaking, your red-blooming geraniums are pelargoniums). Reduce water in winter, watering just enough to keep the potting soil from completely drying out.
In spring, pull the geranium from the pot, gently shake off the old potting soil, and repot with fresh soil. Do not repot in a bigger pot unless the roots are growing out of the drainage holes in the bottom.
You may prune the roots a bit. Geraniums flower better when pots constrict the roots. Also, to get good flowers you must prune back the plant in spring by about half. New shoots will sprout from the old wood.