From Roof Gardens to Alpine Strawberries

alpine strawberry (Fraise des Bois)With rapid change all around us, techniques for growing crops could soon undergo radical transformation as well. Inflation in food prices is due not only to food shortages – brought on by population pressure, severe droughts and vast acreages devoted to growing corn for ethanol production – but to the ever increasing cost of fuel, which makes trucking crops long distances, and keeping them fresh along the way, an increasingly expensive proposition.
The idea of growing food locally makes sense since it solves the problem of transporting crops and takes away the spoilage issue. One of the technologies being promoted is roof gardening.
Agricultural engineers are working on the development of an inexpensive system that would make it possible to grow food on your roof, where water and fertilizer would continuously recycle, having no adverse effects on the environment. You can imagine the beauty of harvesting your dinner salad by ascending a few steps on a ladder and then plucking tomatoes, radishes, cucumbers and lettuce that had been growing above your living room while you were off at work.
Even without high tech growing techniques overhead, there are simple ways of cultivating vegetables on your roof, as long as it’s flat. Here, you apartment dwellers are at a distinctive advantage since the roofs of your buildings are typically flat. Perhaps you can pay some of your rent with fresh veggies that you produce.
On the roof of Rocket Restaurant in Portland, Ore., small kiddie pools are used for growing vegetables. The bottom 2 inches of the pools are filled with gravel or vermiculite and the 4 inches above consists of lightweight soil that is mostly pumice or perlite. Drainage/weep holes, 12 to 18 inches apart, are drilled into the plastic pool circumference where vermiculite meets soil. During irrigation, water is applied until it begins to leak out of the weep holes.
In another technique, described at, growing medium is made exclusively from grass clippings. You start by laying a sheet of plastic on your flat roof. Build a frame from four pieces of wood, as long and wide as you wish. Place the frame on the plastic and fill it with fresh grass clippings. Add water to the clippings and press stamp them down with your feet. Keep the grass moist and it will be ready for seed planting in about three weeks. Plant any sort of vegetable seeds beneath the surface of your grassy bed and they should germinate easily enough. A deeper frame will even allow you to grow root crops such as carrots and potatoes.
Be aware that roof gardening is a more water intensive pursuit than growing at ground level. For this reason, it is essential that mulch be applied on the soil surface, a problem solved by using decomposing grass or straw as growing media. It is also desirable that your roof receive less than all day sun since the heat absorbed from full sun exposure could be overly stressful to vegetable crops.
Still, you will probably have to water your roof garden daily. Regular application of a liquid fertilizer, such as fish emulsion, is advisable. Awareness of flying pests, especially birds, is warranted and protective floating row covers or netting may be necessary.
If you wish to plant ornamentally, not only for aesthetic reasons but for the purpose of providing insulation to minimize heating and air conditioning expenses, a decorative roof covering of sedums is recommended. There are many types of sedums, small-leafed succulents whose colors include red, blue, gold, and every shade of green. Wild flowers and ornamental grasses of small stature may also be used for covering a flat roof. If your roof is slanted, mosses and lichens are the best choices.
At a neighborhood nursery last week, I encountered a plant called culantro. Culantro (Eryngium foetidum) is a relative of cilantro (Coriandrum sativum). Both are members of the parsley family (Apiaceae). Despite the similarity in their names, there are notable differences. Culantro has pricklier, more pungent foliage. Culantro also prefers a partial sun to shady exposure whereas cilantro is happiest in full sun.
A spring flowering vine I never tire of ogling is found at the Van Nuys Boulevard off-ramp from the southbound Ventura (101) Freeway. As you reach the bottom of the off-ramp and come to a stop at Van Nuys Boulevard, look to your right. There you will see a stunning specimen of the yellow trumpet vine or cat’s claw (Macfadyena unguis-cati) growing up a wire fence. This miraculous plant grows year in, year out, with no human supervision of any kind, absorbing the fumes of tens of thousands of automobiles, never watered except by rainfall, yet putting out scads of glossy green leaves and bright yellow trumpet flowers each spring. Owing to its durability, as well as its capacity to root wherever a shoot touches the ground, cat’s claw has been utilized as a ground cover in hard to maintain, out of the way places, as well as on slopes to prevent erosion.
Violet bottlebrush, cousin of the common scarlet bottlebrush, grows in the dirt adjacent to the cat’s claw.
Violet bottlebrush (Callistemon rugulosus violaceus) is a rare plant in our area. It, too, appears to find sustenance in the exhaust fumes that are choked upon daily.
If you have trouble growing supermarket-type strawberries, consider planting alpine Mignonette or wild strawberries (Fraise des Bois). Most nurseries carry seed packets of alpine strawberries, which germinate with ease. Alpine strawberries are smaller and more tart than supermarket strawberries. The advantage in growing them is that they produce fruit practically year around, are adaptable to partial sun exposure and survive freezing weather. Plant seeds now and you will see fruit this summer. Pick fruit as soon as it appears to maximize your harvest.
Several readers inquired about Madeiran cranesbill (Geranium maderense), which was described, but not pictured, in last week’s column. Virginia Snow’s plants are therefore pictured in today’s column.
Tip of the week
“You draw attention to Canary Island plants (in last week’s column),” wrote Andy McKenzie from Redondo Beach. “Add parrot’s beak to your list. It’s a fantastic ground cover that thrives when grown in decomposed granite. It is also an excellent selection for planting in a parkway between sidewalk and street. Just leave some empty space or put down pavers so people can walk across. By the way, parrot’s beak (Lotus berthelotii) is practically extinct on the Canary Islands due to poaching and disappearance of the birds that pollinate it so you are helping to preserve this plant species by growing it.”

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