Are you starved for places to plant produce and flowers in the city? Consider containers and rooftops. Walls are candidates for creating green space, too, and spring is the season for preparing sites and surfaces to support plant life. You can also plant more permanent greenery that will mature over years with proper care.
l Think of containers as you would a garden by planting trees, shrubs, annuals, perennials, and most fruits and vegetables. Almost any plant will grow in a pot — provided the pot is large enough to accommodate the flora.
l Consider the rooftop to be an outdoor level for living. There is a great deal of interest in green roofs. The engineering is a bit more involved than container gardening, but the results are worth the effort. You can insulate your rooftop while creating a prairie, vegetable garden, flower-garden lawn, songbird habitat or other environmentally friendly resource. It’s common sense because it’s good for the planet, and there is more information becoming available about this innovative style of melding soft scape with hard scape, especially because plants use carbon dioxide, produce oxygen and capture particulate pollution. The more plants, the better.
l If you have good light and well-prepared garden soil, you have the perfect conditions for vertical gardening, especially in urban areas where space is limited. Grow fruit or vegetables on a vertical plane for easy access. Flowers grown at eye level provide maximum appreciation. This type of gardening often requires training the plants to perform the way you want them to.
The earlier you prepare, the better head start you’ll have on the growing season. May 1 was considered the “safe” date for planting outside. But early May evenings in the Washington area were cool, so it wasn’t the best time to put houseplants outdoors.
When moving plants outdoors, give them time to acclimatize in a cool room before placing them into full sun and drying wind. Keep indoor trees, shrubs or foliage houseplants in a protected location near your home, or wait for average air temperatures of 60 to 70 degrees before moving the plants.
Planting in pots can be advantageous. For example, if you want tropical hibiscus trees and their beautiful flowers in your garden, you will only be able to grow them in pots — especially if you want to take them indoors to winter. There is only one hardy species in this region that will grow back perennially if planted outside: Common mallow (Hibiscus moscheutos) will return every spring and yield large, trumpet-shaped flowers in summer. However, there are about 200 species of tropical and subtropical hibiscus, and they aren’t cold-hardy. They must be brought indoors in winter and taken outdoors in spring. Planting them in lightweight, weatherproof fiberglass containers is the best way to make moving them indoors easier.
The following are steps to plant large tropical plants that you plan to move indoors in fall:
Almost any object that will hold growing medium and allow water to drain can serve as a container, from a clay pot to a plastic bag with holes for drainage.
The material a container is made of affects watering needs. Fiberglass containers don’t “breathe,” requiring less watering than plants in clay pots. Fiberglass is lighter and easier to move than clay. Unglazed clay pots are porous, and water will quickly evaporate through them. Clay might be more aesthetically appealing, but find plastic or fiberglass pots that look like clay for better moisture retention.
Be sure your container drains well. Make a hole if there isn’t one. If you don’t want to ruin a decorative container with a hole, place a smaller pot inside it and put a couple of inches of gravel on the bottom. A large pot filled with planting medium is extremely heavy, so lighten it by using several inches of perlite or foam-packing material, commonly called “peanuts,” instead of gravel.
I favor a pre-mixed peat-moss-based medium, such as Baccto Professional Planting Mix or Pro-Mix. Garden and home-improvement centers sell soilless potting mixes. Be sure to soak peat-moss-based mixtures thoroughly before planting because they tend to repel moisture until they’re fully hydrated.
Dress up container plantings by using pine bark nuggets as an ornamental mulch. Bags of them are available at garden centers. The nuggets hold extra moisture and can be removed from the top for reuse. Mulches also insulate the growing medium from sudden temperature changes. In a large container, you can use a layer as thick as a two inches.
Hanging baskets or window boxes are an attractive and useful way to decorate walls, lampposts, trellises and balconies. Use plastic baskets that are 8 to 9 inches in diameter to hold three to four annuals such as lobelia, petunias, marigolds and salvia.
Containers can be whimsical and reflect your vocation or personality. A rusty, old pickup truck loaded with flowers could grace the entry to a construction company. A boat full of shore juniper or deutzia could stand in front of a beach house. Flowering vines, such as black-eyed Susan vine (Thunbergia alata) or Anemone clematis (Clematis montana) can drape your front porch for privacy. A pair of brass pots planted with lavender, rosemary, oregano and thyme can be placed at the entry of a cook’s garden, or a wheelbarrow full of flowers could mark a gardener’s residence. If your container is very ornate, it might be more interesting to use it as a sculptural element with only a single variety of variegated grass, such as golden hakone grass in a shady site or porcupine grass (Stipa spartea) in the sun.
The greatest risks for outdoor container gardens, whether they are on rooftops or sidewalks, or flowing from hanging baskets, are drying in the heat of summer and not draining during heavy rain. Container plantings are much more susceptible to drought than flora in the ground and more susceptible to root rot if the base of the pot doesn’t drain.
Watering at planting time is essential, and it’s a good idea to mist plants when first putting them into a container — it can keep them from losing moisture through their leaves. Do not mist after planting. Containers, especially hanging baskets, might require watering every day during the summer if they are in the sun.
Here are some excellent references for more information about making any size home or property a lush green collection of container, patio, wall and vertical plantings:
l “Easy Container Combos: Herbs and Flowers,” by Pamela Crawford (Color Garden, 2011)
l “Easy Container Combos: Vegetables and Flowers,” by Pamela Crawford (Color Garden, 2010)
l “Apartment Gardening,” by Amy Pennington (Sasquatch Books, 2011)
l “Vertical Gardening,” by Derek Fell (Rodale, 2011)
l “Green Roof Plants,” by Edmund C.. Snodgrass and Lucie L. Snodgrass (Timber Press, 2006)
l “Planting Green Roofs and Living Walls,” by Nigel Dunnett and Noel Kingsbury (Timber Press, 2004)
Joel M. Lerner is president of Environmental Design in Capitol View Park, Md.