Thinking outside the window box The Manhattan Gardener

For many New Yorkers, window boxes are pretty much the extent of our gardening space. That’s not to say these aren’t a challenge: watering chores and picking the right plants are even more critical if you’ve only got a few square feet for flowers.

To grow to the max, go for the biggest container that fits your space. A box planter twelve inches deep can hold a rosebush; eight inches deep will support a trio of long-blooming perennials, flowers that come back year after year. Deeper boxes won’t dry out as fast, and you owe it to yourself to visit the second floor of The Plant Shed (208 West 96th Street, west of Broadway) for its wonderland of sizes, styles and materials for planter boxes, window boxes, and urns for the front stoop.

Another option: Go high-tech. Self-watering containers from Gardeners Supply (www.gardeners.com) allow me to leave town for a week without worrying my window box will wilt. These boxes have a water reservoir and come in different styles of lightweight plastic. (I admit I did a faux mossy finish on mine). This online supplier also sells lightweight watering hoses that curl up into nothing but stretch that fifty feet from your kitchen sink to your window plantings.

For a sunny, south- or east-facing window, dwarf rosebushes will give you blooms all summer long. Varieties worth looking for: ‘Happy Chappy’ (single pink flowers) ‘Popcorn’ (ivory flowers with gold centers) and ‘Sweet Chariot’ (fully double, near-purple flowers). Home Depot (90 Third Avenue at 59th Street) carries the dwarf everblooming “Oso Easy”(R) rose series; the newest this year is the apricot-pink ‘Mango Salsa’.

I also like the look of evergreens in window boxes. You get height, you get structure, and a certain sense of dignity, and you can fill in around them with seasonal annuals such as marigolds, petunias, sweet-potato vine, chrysanthemums in fall and ornamental cabbages in winter. For some ideas, just visit New York’s Flower District (West 28th Street between 6th and 7th Avenues), where potted evergreens line the sidewalks every Saturday morning at this time of year.

My own window boxes face north, so for years I’ve relied on sturdy shade perennials for flowers and foliage. Bleeding heart, coral bells, and hosta are all getting upgrades this year, with brand-new varieties worth mentioning to you.

Coral bells -- also known as Heuchera -- are evergreen, but new varieties have leaf colors from apricot to near-black. My ‘Palace Purple’ is easy to find in local nurseries and so strong a plant it will survive even if not watered for a week. A new one I like is ‘Midas Touch,’ with warm golden leaves that will add some lightness to my shady planting.

Old fashioned bleeding heart, with green leaves and pink flowers, has survived nine summer droughts and icy winters in my flower box. ‘White Gold’ offers stunning lime green leaves and white flowers. For a more tropical palette, ‘Gold Heart’ is easier to find, and offers the same chartreuse foliage -- but with hot pink flowers.

Bleeding heart foliage dies down in summer, leaving a space for summer annuals. I’ll usually plop down a pot or two of impatiens until the hosta leafs out fully. Hosta come in all sizes and shades of green, and it’s worth it to hunt for the smaller ones, like ‘Aureo-marginata’ which behaves in containers. This year, I’ve got my eye on ‘Hadspen Blue’ which is a very blue-green and promises purple flowers in August.

Most city garden centers don’t stock spring blooming shrubs, perennials and rosebushes until late March. Early birds head to local growers at the Union Square Farmer’s Market (Broadway at 16th Street) or shop the Flower District. Manhattan’s Home Depot stores start stocking plants in April, and we can expect the newer West Side Lowe’s (2008 Broadway at 69th Street) will do the same.

Can’t find that special plant? Go online. Mail-order nurseries such as Jackson & Perkins, White Flower Farm, Wayside Gardens and Park Seed are reliable and usually offer online specials if you sign up for email alerts.

Mia Kravitz is the author of The Garden Explored and has been gardening in the city since 1979.