American visitors have always admired the colorful window boxes on Swiss homes. These planters are filled with mound of cascading ivy geraniums. Gardeners want to know if these plants can be grown like that in our part of the world. The answer is yes, if the proper growing conditions are provided.
Ivy geraniums (Pelargonium peltatum), are not as commonly grown as their cousins, zonal geraniums (Pelargonium x hortorum), but are becoming increasingly popular for hanging basket or window box planters. They are native to the Cape Province of South Africa where they grow in sheltered places. The species was first introduced into Holland in 1700 and into England in 1774.
Today there are more than 75 different commercial cultivars. They vary in foliage color, size, variegation, bloom color and growth habits. Most of today's ivy geraniums are asexually propagated by rooted cuttings. They root easily in a moist, porous, well-drained rooting medium, such as perlite. Ivy geraniums can be grown from seed and germinate under similar conditions as P. X hortorum (see HHPN, 1995, page 4) The seeds are sown in January for optimum-sized transplants in the spring. The recommended cultivars of ivy geraniums to grow from seed are the 'Tornado' series or 'Summer Showers'.
The ivy geraniums seen in the Swiss window boxes or balconies are often the mini-cascade types of the Balcon or Balcon-type geraniums. Although they begin to bloom a bit later and have smaller flowers than common ivy geraniums, they are much more floriferous and become a mass of bloom trailing two feet from a window box, even on the north side of a house. The flowers are "self-cleaning:" and do not require dead-heading.
There are many good ivy geranium cultivars on the market. Some of the common varieties that have stood the test of time and are still popular are: 'Sybil Holmes', 'Beauty of Eastbourne', King of Balcon', 'Amethyst', 'Cornell', 'Salmon Queen', and 'Mexicana'.
The beautiful 'White Mesh' and 'Crocodile' are two very unusual ivy geranium varieties. The veins in the leaves are bright white. This leaf variegation is caused by mesh-vein virus. This virus is quite difficult to transmit and it appears to have no pathogenic effects. In hot weather the variegated foliage pattern is lost, apparently through virus suppression by heat. Fortunately, the variegation returns when temperatures are more moderate.
Ivy geraniums are unique in their cultural requirements and should not be treated the same as common zonal geraniums. Light and temperature are two factors that should be considered. Ivy geraniums prefer moderate temperatures. If the temperatures are between 65 and 80 degrees F, place the plant in full-sun a location. When the temperatures are above 85 degrees F, hang the plant in a location that receives partial sun. Varieties also differ in their response to light levels. Too much light sun may result in small, cup-shaped leaves and small blooms. If in doubt, hang the plant in a location that receives afternoon shade.
Ivy geraniums require moderate soil moisture levels - not too much and not too little. One of the major problems seen on ivy geraniums is edema, a physiological disorder caused by inconsistent moisture levels. It is characterized by many corky spots of varying size on the undersides of older leaves. The stress caused by too little and too much water leads to ruptured plant cells and the formation of scar tissue or corky spots on the leaves' undersides.
Ivy geraniums are relatively pest-free. The primary greenhouse pests to be on the look out for are mealybugs, red spider mites, and thrips. The best pest control practice is to purchase pest-free plants.
Fertilize ivy geraniums as you would other container gardens or hanging baskets. A soluble plant food applied with the watering about once every two weeks should be adequate.
Besides hanging baskets, ivy geraniums can also be used as a ground cover in a protected location and in containers combined with other annuals that add contrast in color and foliage.
This article originally appeared in the May 10, 1996 issue, p. 73.