Creating a City Rooftop Garden

I knew that water retention is important for
container-grown plants — especially when they’re
exposed to as much heat as the crops in my hot-tin-roof
garden would face — so I was careful to use only
plastic (or plastic-lined wooden) containers. (Clay or
fiber pots would have dried out too quickly.) Also, for the
same reason, I drilled only two or three drain holes in
each receptacle. And I decided to use pure compost as the
growing medium, because humus holds moisture much better
than run-of-the-mill dirt or commercial potting soil.

Fortunately, the small city where I live composts its
leaves and grass clippings, and lets anyone mine the
resulting black gold, gratis. So I loaded the back of my
station wagon with drain-hole-drilled containers, filled
them at the municipal compost pile, traveled back to the
co-op, lugged the heavy pots up two sets of stairs and out
a second-story window, and positioned them in my
garden-to-be — and then repeated the whole laborious
process several times, shuttling back and forth (and down
and up) until some twenty-odd casks of compost were in
place.

It was difficult at the time to appreciate what all that soil
and sweat would eventually yield. But at the end of the
day, when I put in my first planting — three dozen
onion sets in a plastic foam grape box — I already
felt that simply having a garden was worth all of the work.

Planting a Rooftop Garden

Almost any kind of vegetable will grow in a pot . . . but
that doesn’t mean it will thrive , or that it will
produce bounteously. So when it came to deciding what to
grow in my by-the-gallon garden, I took two factors into
primary consideration: the space required — both
above and below the soil — and the expected yield. I
immediately ruled out pumpkins and similar sprawling vine
crops, as well as root crops (such as daikon radishes) and
other veggies that have extensive or deep root systems. And
I also vetoed spare-hungry, low-yield crops such as corn.
(I knew that a five-gallon bucket of corn wouldn’t produce
much of a harvest!) The value of the yield was a
consideration, too. I can buy a 50-pound sack of potatoes
for less than $3.00, so I figured it would be silly for me
to grow spuds.

Just what did I plant, then, besides scallions?
Well, my spring crops were red leaf lettuce, Swiss chard,
chives, radishes, kale, and collards. My summer plantings
(which I was able to put in two weeks earlier than usual,
thanks to the heat-holding roof) included cherry tomatoes,
pickling cukes, green peppers, yellow squash, bush beans,
and parsley. I also added marigolds, coleus, sweet
woodruff, and oregano . . . simply because no garden is
complete without the color of flowers and the fragrance of
herbs.

I planted my seeds in a conventional manner, using
traditional depth and spacing guidelines. The onions sets
in the grape box, for instance, were planted on two-inch
centers — common spacing for intensive scallion
production. Lettuce, which also did well in grape boxes,
was seeded directly in three rows about four inches apart
and then heavily thinned throughout the season. The larger
plants — tomatoes, peppers, collards, etc. —
were purchased as seedlings; each got its own five-gallon
tub from the first.

The melon crate that I lined with Mylar (to hold in both
moisture and dirt) became a garden unto itself. It was by
far the largest container I had (about 30 gallons), so I
sowed three crops in it. In the back half, a row of
pickling cukes, interplanted with some dill, climbed a
space-saving trellis. And in the front was a double row of
green beans. Although the box eventually looked pretty
crowded, all of the plants stayed healthy throughout the
summer.

In general, though, a rule of thumb for the container
gardener is oversow and then thin ruthlessly . I
learned that lesson when my unthinned chard never got more
than nine inches tall — puny in comparison to the
lush fronds I’d grown in my raised-bed past.

Another danger to vegetable vitality — particularly
for squashes and their cousins — is transplant shock.
I sowed six yellow squash seeds in each of two five-gallon
buckets and then, about a month later, carefully (or so I
thought) transplanted all but one plant from each bucket
into other containers. The two undisturbed plants remained
hardy and produced well, but their transplanted siblings
were stunted and never bore fruit. Except for tomatoes,
peppers, and other tropically inclined cultivars that
appreciate a start indoors, rooftop garden crops can (and,
I found, should ) be started in the same
containers in which they’ll mature.

Rooftop Garden Maintenance

The most important word in the container gardener’s
maintenance vocabulary is water — or more
precisely, watering , which is what I ended up
doing almost daily throughout June, July, and August. The
high heat and low humidity of the rooftop environment
caused my green charges to be much thirstier than their
earth-bound counterparts would be. When you add those two
factors to the others that were at work — low
moisture retention (in even the best tubs), shallow root
systems, and a Sahara-dry summer — it’s no wonder I
lugged at least ten gallons of water up to my rooftop
garden every day the sun shone. (Looking back, ten gallons
a day doesn’t seem to be all that much . . . but an outside
faucet and a hose sure would’ve helped.)

Container gardens also have special fertilization needs,
mostly because the soil isn’t a part of a natural
nutrient-building environment the way the soil in a “real”
garden is. My vegetables and flowers gradually used up the
nutrients in their pure compost . . . and I’m sure the
daily waterings washed some nutrients out through the pots’
drain holes, too. So, around the end of June, I started
adding weekly doses of fish emulsion and liquid kelp to the
water. Potent commercial fertilizers might have produced
greener, lusher growth, but I couldn’t imagine having a
non-organic garden — even one growing in
petrochemical-based plastic buckets!

A Few Plant Growing Problems

Being organically inclined, I also declined to grab a bottle of bootleg DDT at the first sight
of cabbageworms chomping their way through my collards.
Instead, I sent many of the little rascals splatting to
their ignoble ends on the parking lot below. But since
there were a lot of them and only one of me, and because
they are good at hiding, I finally resorted to a few
applications of Bacillus thuringiensis , a
microorganism that gives caterpillars a terminal case of
upset stomach. The only other noxious insects that came
calling were aphids (on a stunted kale plant; aphids always
know which garden crop is the weakest) and a few Mexican
bean beetles — but neither pest became much of a
problem.

My pail-grown produce also escaped the ravages of disease,
even though the plants occasionally suffered from moisture
stress (whenever I was away for a few days and unable to
water). Moisture-stressed plants are usually more
susceptible to disease (and insect) attack, but mine came
through admirably. Weeds weren’t a problem either; only a
few emerged from the leaf-and-grass-clipping compost.

One minor problem that did need attention developed after
some plants became rootbound and the dirt shrank away from
the sides of the tubs. I had to tamp new soil down into the
gaps; otherwise, at watering time the liquid would have
washed right over the edge of the compacted compost, down
the sides, and out the drain holes.

Looking Back

Some gardeners — like some fishermen and hunters
— find more pleasure in the process than in the
harvest. Doing becomes its own reward.

So it was with me and my rooftop flower-and-vegetable
patch. The yields were less than spectacular.
Sure, I had more lettuce than I knew what to do with. The
peppers were prolific. There were lots of scallions in the
spring and more than enough cherry tomatoes throughout the
summer. And I usually had a meal’s worth of collards and
kale every week. But I still had to buy most of my
fresh veggies downstairs — from the co-op’s produce
case.

Nevertheless, my pot-bound plantation was fun. And it was a
learning experience that I can draw upon again, if
I ever have to (fortunately, I’ve since moved to a place in
the country where there’s lots of ground-level
growing space). But most important, my container garden
gave me a place to relax and restore my spirit. Lounging
among the plants on that roof, watching the bees move from
flower to flower, I felt as though the city streets were
miles — instead of just two stories — away.