Ivy geraniums, technically Pelargonium peltatum, are not as well known as their cousins, the zonal geraniums, but have much to recommend them. Their flowers, in shades of pink, are slightly smaller but numerous and their leaves are glossy and attractive. Their somewhat trailing habit is useful for window boxes and hanging baskets. Like other geraniums, they are easily grown from cuttings and may be overwintered as small plants on a sunny windowsill.
Ivy geraniums like an acid growing medium, with a pH between 5.1 and 5.6, about the same acidity as soil for blueberries, azaleas and rhododendrons. Use a potting soil prepared for these kinds of plants or add peat moss to lower the pH of a general mix. Also add vermiculite or perlite to lighten the mix and help it drain more quickly. Never use garden soil. It is too dense for good root growth.
Take 3- to 4-inch cuttings from the growing tips of branches in fall for overwintering or in spring if you have plants that have been kept in a greenhouse. Remove the leaves from the bottom 1 to 2 inches and push them into the potting mix. You can dip the cut ends in rooting hormone, but since they root so easily this is not usually necessary. Water the cuttings well. Keep them in a spot that is light but not sunny until they are well rooted at a temperature between 65 and 72 degrees Fahrenheit, somewhat cooler at night.
Several varieties of ivy geraniums are available from seed. Sow in small pots and cover with 1/8 inch of soil, then moisten with a spray bottle. Place the pots in clear plastic bags to keep them from drying out. Light is not needed for germination, but the seeds should be kept warm, between 70 and 75 degrees. Seeds will germinate in a week or two and when you see small green leaves, remove the plastic bag and place pots in a sunny location or under fluorescent lights for 12 to 14 hours a day.
As the seedlings grow, fertilize weekly with a liquid fertilizer diluted to half strength. You can transplant them after they have a few true leaves or thin them by removing the weakest ones. Plants grown from both cuttings and seeds should be hardened off before being moved outdoors by leaving them outside for a short while every day for a week, increasing the time from a few hours to five or six.