The best advice when buying plants for your railing planters or hanging planters is to go to a reputable garden centre or nursery. Bedding plants are sold in strips, but larger plants such as ivies, pelargoniums and fuchsias are usually potted individually. ‘Plugs’, basically young plant-lets with well-developed root systems, are often sold via mail order by seed merchants; Busy Lizzies, Fuchsias, Pelargoniums and Begonias are often marketed this way.
If possible check the plant before purchase to make sure that it is not harboring any pests or diseases. Bedding plants should have fresh, bright green foliage, with no hint of yellowing, and should be compact, not straggly. Potted plants should have a good root system.
If you can, slide the plant from the pot. The roots should fill the pot nicely without being tightly coiled. Select plants that have plenty of healthy buds that are not yet open. Bulbs are sold when dormant (usually in autumn and winter). Buy them from a reputable garden centre or nursery and look for firm, plump bulbs that show no signs of withering or fungal disease.