In her 1962 book Silent Spring,
Rachel Carson told a story about robins and worms. The story went like this: Elm trees were being sprayed with DDT, an insecticide used to combat
mosquitoes and lice. In the fall, the
elm trees dropped their leaves, and those leaves were devoured by earthworms
living among the roots of the trees. But here was the surprise: Earthworms, as it turns out, have an amazing ability to absorb some of
the substances that they find in the soil. In this case, they were able to take up huge concentrations of DDT into
their tissue and still live.
In the spring, the natural life
cycle of worms and birds played itself out as usual: The worms came out of the ground at night; the birds foraged for
stragglers early in the morning. But
this time, the robins that ate worms also ingested what was stored in their
tissue: a massive, concentrated dose of DDT.
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Eating only eleven worms with a
concentration of DDT would be enough to kill a robin, and when you consider
that a robin can eat 10-12 worms in an hour, it’s no surprise that the worms
were toxic enough to kill them. Some
robins survived the high doses of poisoned earthworms, but were infertile and
did not lay eggs the following spring. Others had trouble building their nests.
DDT was eventually banned in the
United States, thanks in part to the public’s reaction to Rachel Carson’s
book. But this story has relevance to
gardeners even today, because it reminds us that the birds and insects and
plants in our gardens are connected in ways that we might not foresee.
Perhaps that’s why so many
gardeners who are serious about attracting birds, insects, and wildlife to
their gardens try to minimize the use of chemicals. After all, a natural garden need not depend on synthetic products
to stay alive—in fact, it seems to go against the spirit of the
enterprise. Here are some natural
approaches you can take to keep your garden healthy, and minimize the impact of
pests, disease, and weeds.
Feed the Soil
A garden
thrives on rich soil that is teeming with life. One small vegetable bed can
contain thousands of earthworms, mites, springtails, ants, and spiders. There
could be several million nematodes in that patch of earth. But the other tiny,
unseen microbes in the soil—bacteria, fungi, and protozoa—outnumber all those
other creatures combined. A teaspoon of soil can hold a billion bacteria.
I once
explained all this at a composting workshop and offered some suggestions for
increasing the bacterial population of compost. “Bacteria!” a woman shrieked
from the back row. “In MY compost?” She was appalled. But the fact is that the
microscopic population of your soil is what supports and sustains plant life,
prevents disease, transforms nutrients into a form that is easier for plants to
use, and improves soil texture. Once you know that, feeding your plants
chemical fertilizers starts to seem pretty silly. It would be like you trying
to survive on a multivitamin alone, and not a very good multivitamin at
that—one that contains, for instance, only vitamins A, C, and D.
Let me
explain about those three vitamins. The
numbers on a package of fertilizer describe the concentration of three major
plant nutrients: nitrogen, phosphorus, and potassium. A 10-10-10 fertilizer
contains, by weight, 10 percent nitrogen, 10 percent phosphorus, and 10 percent
potassium. Synthetic fertilizers tend to have higher concentrations of these
nutrients, which is why a 10-10-10 or 20-20-20 product is almost certainly synthetic.
Organic fertilizers, which are derived from natural sources like bone meal,
alfalfa, and fish emulsion, tend to have lower concentrations like 5-5-5 or
even, in the case of a product like kelp meal, 1-.2-1. But even though organic
fertilizers offer up smaller doses of those major nutrients, they are derived
from natural sources that feed the soil over the long term.
Well-Balanced Diets
Those three
major nutrients are important, no doubt about it. Nitrogen promotes green leafy
growth and is important when plants are leafing out. Phosphorus encourages
flowering and fruiting; you might use more phosphorus in the summer when
vegetables are just setting fruit. And potassium is critical for strong root
development and for helping plants to resist diseases and withstand extreme
heat or cold. But those aren’t the only nutrients that plants require:
secondary nutrients like calcium, magnesium, and sulfur are essential for plant
growth, and micronutrients, or “trace elements,” like zinc, iron, copper, boron,
and manganese, are also necessary in small quantities for chlorophyll formation
and stimulation of plant growth hormones.
All those
microbes living in the soil consume organic matter and help convert these
nutrients into a form that is easier for plants to use. When you hear gardeners
talk about “feeding the soil,” what they’re really talking about is feeding
this army of tiny soil-dwelling creatures, who will, in turn, feed the plants.
So how do you feed your garden a well-balanced meal?
Mulch your plants well with aged compost and manure. That will keep moisture in
and add plenty of beneficial microbes to the soil. To support fruiting and
flowering, consider using bat guano or bone meal. Try a foliar spray, a watery
mixture of kelp meal or fish emulsion applied directly to the leaves of the
plants. Look for a dry organic fertilizer that you can mix into the soil or
water into existing plantings. And
remember that healthy soil encourages earthworms. That’s good for the plants and good for the birds that get up
early enough to grab them.
Bountiful Insects
You may not think that the best
strategy for pest control is to lure more bugs to your garden, but that’s
exactly what organic gardeners do. Ladybugs larvae devour aphids. Green lacewings, damsel bugs, beetles,
wasps, and other insects also help keep an overpopulation of “bad” bugs in
check. The trick is to plant what they like. Many beneficial insects are
attracted to plants with tiny flowers, so try yarrow, alyssum, and tansy. Let a
few herbs go to seed—cilantro, dill, fennel, and carrots all lure beneficials.
Then be prepared to put up with a little damage from the bad bugs—after all,
the point is to reach a balance and provide a small, but sustained, food source
so that beneficials will stay around. Best of all, a healthy insect population provides plenty of food for
foraging birds.
Traps and Lures
Many nurseries sell yellow sticky
traps that will lure aphids and whiteflies to their death. You can also use
particular plants as a trap crop. For instance, plant mustard greens to lure
flea beetles away from more valuable crops like cabbage or arugula. Nasturtiums
can attract aphids away from roses. Lovage is a herb that tomato hornworms
enjoy; plant some near tomato plants to lure the nasty green caterpillars away.
Monitor the trap crop closely, and when it’s fully infested, rip it out and
throw it, and its inhabitants, away in a sealed bag.
Microbial Creatures
Organic gardeners have learned to
use the power of beneficial nematodes to combat soil-dwelling pests. These
microscopic creatures exist naturally in your soil, and each species has its
favorite food. You can buy nematodes to combat cutworms, fleas, and even other
nematodes, such as the one that causes root-knot in carrots. They come suspended
in a solution that is soaked into a sponge: to apply the nematodes, you just
drop the sponge in a bucket of water and then spray the nematode-soaked water
around the garden. Also, some organic
fertilizers now include beneficial bacteria and fungi that also help fight
diseases.
Natural Solutions
Try spraying insecticidal soap or a
mixture of dishwashing liquid and water on aphid-infested plants. It’s very
effective against soft-bodied insects but does not harm beetles and other good
bugs. A spray made with water, garlic, and chili pepper also works against
aphids and whitefly. A teaspoon each of baking soda and liquid dish soap, mixed
with a quart of water, can help fight fungal infections like blackspot and
powdery mildew.
For serious infestations, consider
a dormant oil to smother pests; or spray with rotenone/pyrethrin, a plant
extract that targets potato beetles; or Bt, a bacteria that causes caterpillars
to stop feeding and die. Just remember that organic gardeners use these
products sparingly and only apply them after they have diagnosed the problem
and made sure that the product will work against that particular pest.
Knowledge is the organic gardener’s best weapon; even a natural pesticide
should never be applied in a “broad spectrum” manner that might upset the
natural balance of insects in the garden.
Prevent, prevent, prevent
Pick off diseased foliage and throw
it away. Use natural solutions early before serious infestations take hold. And
use compost, mulch, and organic fertilizers to grow strong, healthy plants that
can tolerate a little damage.
Kill weeds the old-fashioned way
There are plenty of natural
alternatives to pesticides. A solution of 5-10% vinegar mixed with water will
kill weeds, and pouring boiling water on weeds growing between cracks in the
pavement is another great home remedy. Smother weeds with mulch and plant
perennials close together to crowd out weeds. And if your garden does get
overrun, as mine does every year around this time, just remember that pulling
weeds is, after all, great exercise and an excuse to spend more time in the
garden enjoying the abundant life around you. And isn’t that what it’s all
about?