Most plants do best if they have room to spread their roots out, extending their reach for water and nutrients. Pots, on the other hand, confine a plant's roots in a small space but can be quite successful. Think of shallow soil less than 20 inches deep, as a wide container, not ideal but not too much of a problem if you remember to give plants extra water and fertilizer.
The Herb Garden
Rosemary is a small, aromatic shrub with a dense root system that does well in confined spaces. It is drought-tolerant, loves sun and warmth and has the best flavor when grown without fertilizer. Combine it with other Mediterranean natives such as thyme, sage and lavender. Not only do the gray-green needle-like leaves look well with the gray of the lavender and the deep green of the thyme, the plants all prefer the same amount of water and sun. Add gravel, perlite or sand to your soil to make sure it drains well.
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The Annual Bed
Annuals are ideal for shallow soils since they need no permanent root system. Petunias, for instance, have large flowers, up to 2 inches across, in a wide variety of colors and do well in both sun and part shade. They grow quickly, forming mats a few feet across that trail slightly. Match them with flowers of a different texture or height, perhaps upright snapdragons, also with a wide range of colors and short, medium or tall varieties. Delicate lobelia comes in white and several shades of true blue and will fill in gaps between other annuals. All these prefer regular watering and occasional applications of fertilizer.
The Perennial Bed
Use low- to medium-height perennials such as daylilies, tough plants for sun or part shade with solid root systems that can be neglected once they're established. The newer varieties of daylilies expand the color range from golds and oranges to pastels and cooler colors. In part shade, pair them with hostas, ornamental foliage plants with broad, ridged leaves often variegated with white or yellow. Then, for contrast, plant ferns and daffodils for spring color.
The Shrub Bed
Low shrubs such as heathers and miniature roses will do well in shallow soil. Heathers prefer sun and regular water, but by choosing different species you can have flowers in spring, summer or fall. Miniature roses are often sold as houseplants but are just as hardy and easy to grow outdoors as the taller varieties. Give them full sun, fertilize lightly several times a month and keep the ground moist but not wet.
The Vegetable Bed
Leafy greens like lettuce and spinach are excellent for containers or shallow beds. Give them plenty of water, regular fertilizer and some lime if the soil is at all acid. Beets and radishes also do well, but if you want to grow carrots, stick with the shorter varieties.