Amazing Weed Diversity
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| Every once in a while nature exhibits astonishing diversity. It
is especially welcome in the heart of the city. Twice I was thus amazed
with weed populations. The first time was November 21st 1981, in
the arboretum. In a mulched bed of azalea bushes, an area approximately
10 x 20 feet, grew 42 different kinds of weeds! It seems the compost
applied as mulch was full of seeds; some seeds also blew in from nearby
trees. Never since have I encountered such weedy diversity in 200 square
feet. But recently an area nearly six times larger did host enough weeds
to warrant a census. Here's the story. |
| There was a boring grass parking strip 10 feet wide and 117 feet
long, or 1,170 square feet. In late October workers used a sod cutter,
removed the sod, and evenly spread 15 cubic yards of Pacific Topsoil's winter
mix. This mix consisted of peat, composted manure, coarse sand, and
soil. Then 3,500 starts of ivy were planted, along with 600
Narcissus 'Thalia' bulbs. So far, so good. The bulbs gleamed brilliant white in bloom
this spring, and the ivy is growing. But on June 6th, this ivy and
Narcissus bed hosted 66 different weed species! Doubtless a few were overlooked in
the census, and some summer annuals had barely sprouted. For purposes
of the inventory, any kind of plant that sprouted was called a
weed --since none were desired except ivy and
Narcissus. Don't blame Pacific Topsoil, because each mix varies in its seed content, and not all are jackpots
of diversity. Moreover, some seeds blew in from nearby areas. |
| An analysis of the weed species showed only 5 were native. At least
to botanists, this means they were growing in Seattle since the last
glaciation some 13,500 years ago. The other 61 species were all newcomers
from elsewhere, mostly Europe. Similarly, the 42 weeds in the
arboretum azalea bed included only 7 native species. |
| Let's pretend the gardeners never got around to weeding these
sites. They were too busy. Then what? At the arboretum, the following
tree seedlings would've come to dominate the site: birch, cottonwood,
Douglas fir, mountain ash, English oak, and willow. In other words,
"the urban forest" would have reasserted its presence. As for the 1,170
square foot ivy bed, its trees were different: birch, crabapple, black locust
and bigleaf maple --also plenty of blackberry and Scotch broom. Left
alone it would have evolved into a rich and lovely scene, actually. Much
more interesting than a lawn. |
Carrying all this observation to its theoretic extreme, if
all people stopped weeding, Seattle would become forested, everywhere.
"Weeding" includes mowing, spraying herbicide, brush control, etc. We
should be grateful for Mother Nature's resiliency, and delight in the things
she does. It is conventional and convenient to call "weeds" every plant
which sprouts wild in a place where people desire only those plants we
specify --or desire no plants at all. But really, Nature's just doing what she has
been doing for more than 250 million years --botanists estimate that
seed plants have been around for at least that long. Yes, soil is the seedbed,
then arena, for an endless plant wrestling match. If people fashion our
weapons into hoes, and give up fighting for gardening, we might just
recreate Eden.
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(originally published in The Seattle Weekly, June 1997)
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