Since houses are painted various colors, some bright, others dark, window boxes can be colored to match. A light blue house, for example, can have dark blue boxes or boxes in a harmonizing color. Against weathered shingles, blue is pleasing.
On a dark red house with white trim, white boxes with blue and white flowers look well, and in all-white boxes, green and variegated foliage plants are attractive. A white house offers every possibility. Boxes may be of red, pink, lavender, blue, gray, turquoise, or rust, although trim is sometimes a factor.
With a bright color like red, limit flowering plants to one color. I once saw a blue house, with white trimmings
and blue boxes, planted with large hybrid white petunias -a cool, effective combination. Also delightful were blue boxes, with pink geraniums, white alyssum, and blue lobelia on a white house with blue shutters and trim.
Usually with a traditional house conservative green or black boxes look best. These are the colors of the window boxes on Beacon Hill, Boston, chosen to adorn the nineteenth century brick facades. Where the period is not a consideration white or cream-colored boxes look well on brick.
To hold window boxes securely, use bolts or lag screws and treat them beforehand to prevent rusting. Leave an inch or so of space between box and house for the movement of air. If boxes are to rest on a terrace or other solid surface, raise them on cleats or set up on bricks or blocks of wood so drainage holes won't become clogged. Some space under boxes is also important for air circulation, which will dry up run-off water.
When you plant a box, put an inch layer of broken flower pots, crushed brick, small stones or pebbles over the bottom to enable water to escape freely through the openings. Above this, spread a piece of wet burlap or a layer of moist sphagnum moss, old leaves, hard coal clinkers or cinders to prevent soil from washing into the drainage area. If you use cinders, first sift to remove ashes, then break up with hammer or stone into half-inch pieces. These will let water pass through, yet retain moisture and some of the fertilizer that washes down.
Soil and Spacing
Plants in boxes need rich soil for luxuriant growth. Space larger kinds-geraniums, coleus, and fuchsias-eight to ten inches apart; smaller kinds-lobelias, annual phlox, wax begonias, sweet alyssum, and browallia-six inches apart. An eight-inch-wide box accommodates two rows of plants, with the tall ones in back and the low ones along, the front. Boxes, ten inches wide, take three rows of plants, tall, medium, and low for edging.