How do I grow geraniums? Are there native species I can grow?
The answer to this questions depends on whether you are referring to hardy geraniums (cranebills) of the genus Geranium (picture below)
or to another group of plants commonly called "geraniums" but which actually belong to the genus Pelargonium (picture below).
Hardy geraniums or cranebills
There are about 300 species of cranebills world-wide, of which about 50 are grown as garden plants. Scores of varieties have also been developed. Pink, blue, white and purple flowering varieties can be found. They are hardy perennials grown in full sun or part shade. Several species can be grown as a ground cover. Most species are relatively easy to grow and will thrive in a variety of conditions. A recently introduced variety 'Rozanne' has become very popular.
There are three species of geraniums native to the United State - Geranium maculata (spotted, wood or wild geranium), G. carolinianum (Carolina geranium) and G. bicknellii (Bicknell's cranebill). The spotted geranium is often grown in gardens and can be used as a slow-growing ground cover. It is relatively deer-resistant.
Pot geraniums or Pelargonium sp.
Unlike hardy geraniums, pelargoniums are tropical plants grown as annuals in the Northeast. There are about 200 species of Pelargonium in the wild. Cultivated pelargoniums originate mainly from South African species. They are very popular plants and more than a thousand varieties have been developed.
There are two main groups of these geraniums - upright geraniums (P. x hortorum) and ivy or trailing geraniums (P. peltatum). The former are grown either outdoors in the garden or in pots whereas the latter are grown mainly in pots, often in hanging baskets.
Upright geraniums (either so-called seed-producng or cutting-produced [zonal] species) should be grown in locations that get at least 6 hours of sun daily when grown in the Northeast. When grown in flower beds, 30-50% of compost should be added to the soil to improve drainage. Complete dry fertilizer or slow-release fertilizer should be added at the same time. The plants need to be well watered all summer but the soil should be allowed to become dry between waterings. Additional fertilizer should be added periodically. If the leaves become yellow or the flowers smaller, these are signs of poor nutrition. For best results, dead flowers and leaves should be removed weekly.
Pot geraniums can be overwintered in several ways. One way is to dig up the plants before the first frost, cut the shoots down to about half their size and carefully remove soil from the roots. The plants can be then be stored in a cool, damp location. If they show signs of shrivelling then they can be sprayed with water or even dipped in water for a short time. They can be re-planted outdoors once the danger of frost has passed. Plants can also be saved by potting them in potting soil and keeping them indoors in a sunny location. Finally, cutting can be taken and grown indoors over the winter in a sunny location.
Trailing or ivy geraniums can be grown under the same conditions as upright geraniums although they will tolerate less light. They are heavy feeders and should be fertilized regularly. They do not require dead-heading.
Pelargonium geraniums can also be grown in pots, window boxes and hanging baskets. Under these conditions it is especially important to use proper watering and fertilizing protocols.
Fischer USA, Inc has published a useful information sheet on geraniums- http://www.milmont.com/_ccLib/image/articles/PDF-20.pdf.
Courtesy of NYBG Plant Information Service