InsatiableGardener.com

Image by claireg73 via Flickr

by InsatiableGardener.com

Roof Top Gardens

Whether on one-story structures or on skyscrapers, rooftop gardens are havens with a charm of their own. For the owners, they provide private worlds in which to grow plants and escape the bustle of city life. All this, of course, is made possible with soil brought in and carried to the top of the building for the pots and boxes that comprise the rooftop garden. If you have ever seen a penthouse garden, you know what a feeling of space it gives, especially if the building is high. It is like being on a mountain top, with a panoramic view that on clear days seems limitless.

Build Windbreaks

Delightful as these skyline gardens are, they do present problems. The wind, for example, snaps trees and tears up plantings. Arrangements must be made to provide shelter in the form of fences or other barriers. These also give needed privacy. Winds constantly dry out the soil so that in summer when the sun is hot, plants often need watering two or three times a day. Pergolas, lattice fences,wood panels, and laths can be erected to provide shade but still allow air and sun to enter.

Winter cold is another problem. In cold regions, where soil freezes solidly, evergreen plants are often wind burned through loss of moisture that is hard to replace when the soil is frozen. The sun, too, draws off moisture and causes sunscald. Rooftop gardens only a few stories up are less affected by wind and are often easier to care for than plantings on the ground. They are usually protected by buildings on one or more sides and get sun for only a part of the day.

Roof Must be Strong

At the start make certain the roof is strong enough to support the weight of containers filled with soil. Modern buildings usually are, but you will be wise to have your structure checked by a building inspector. Then make sure that water can be drained away through pipes. Most important, build a wall around the edge of the roof high enough to serve as a guard. This can be constructed with some harmonizing materials such as concrete, brick, and wood.

The next step is to make a plan. On the whole, simple, formal designs are best in the limited area of a roof. Allow for some large boxes for trees and shrubs and for raised beds, which will give the feeling of flower borders. Erect fences and lay out several enclosed areas for dining, sunbathing, and reading.

Only those who have lugged soil in baskets and boxes onto elevators or up flights of stairs know what this involves, yet without it there can be no garden. If you go to all this effort, obtain good soil, since the labor and cost for good and bad soil are about the same. As for containers, be certain they are large enough to hold sufficient earth. Shrubs, vines, and roses need a depth of eighteen inches; trees need considerably more. For perennials, annuals, and bulbs, a depth of ten to twelve inches is satisfactory. If boxes are equipped with wheels, it will be easy to move them around and water will pass through the holes without interference.

Since rooftop space is limited, try to have boxes fit specific areas. Here is your opportunity to introduce interesting shapes suited to the overall design. If you set up boxes in step fashion, you can grow more plants in a limited area. Allow some space for vines and espaliered plants to cover walls, fences, and other vertical surfaces.

Instead of adding soil to all the containers, fill a few of the largest with moist peat or sphagnum moss. Flowering potted plants can be plunged directly into these and be replaced when they are past their prime. This may be expensive, but it always seems worthwhile, and you do not have to replace a large amount of worn-out soil after a period of years.

Planning A Primrose Path

An area of any size, a path of any length, or even a simple wooded corner has in it a potential Primrose Path. Whether four feet long or four hundred, it can have charm. It isn’t necessarily length and size that make for success, but rather an indefinable element compounded of composition, arrangement, Tightness, and vigor of the plant material involved.

The soil on our Primrose Path is partly composed of rotted leaves and old stumps. It is rich and black and loose, and almost always slightly moist to the touch. The nearby stream runs with ample water the year round, and in flooding spring rains the primroses are occasionally under water. Our slope is slight and to the southwest. The plants bask in morning sun briefly till about eleven, when trees shade them, then again filtered sunlight dapples them through the afternoon.

Of course a brook isn’t essential. And primroses will thrive as happily on east, south, or west slopes—but not so well on the north.
They definitely do want a cool moist area, and shade from the noonday sun. In other words if your land is high, dry, and hot, better to plant marigolds!

We have well over a hundred plants now, and our goal is unlimited. Each year we buy a few more from the catalogues, the local nursery, and the grocery store. (You can successfully transplant primroses in full flower.) Every year we also start more plants from seed (partly because a thousand of anything is costly).

Plant seeds outside in May, in a small six by six seedling corner of the vegetable garden that gets five hours of sun daily. We sow seeds one eighth to a quarter of an inch deep in light well-drained soil. In two weeks or so seedlings first appear. We thin them to stand six inches apart.

In the fall we cover the small thrifty plants with pine or evergreen boughs, and then leaves. The boughs prevent the leaves from packing on the crowns. The plants remain in the nursery through the first winter. Early the next spring they are set on the Primrose Path.

We dig a hole and loosen the soil in the area around it, giving each plant a site with plenty of good growing room. We free it from roots and encroaching greenery. A few trowels full of leaf mold or superphosphate mixed in the earth under the plant is helpful. Set each plant and firm the soil up around the crown but never cover it. Water, and then the fun begins. Observe how they take hold and grow. If there are normal spring rains no further watering is needed.

One of my favorite pastimes is to wander in our nearby woods with a small dump wagon or basket, collecting leaf mold and material from inside old rotted stumps. Both can be used in or on top of the soil, and will greatly spur primroses to their best. Many of the first-year plants will flower the following spring on the Primrose Path. They’ll be tentative, small blooms, to be sure, and only a few, but enough to reveal colors. The subsequent spring they really let go and bloom riotously.