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Gardening - Soil-Building Strategies
In certain religions,
one step on the path to enlightenment is to sit in the lotus
position and chant "OMMMMM." That, in two letters, is the game here:
O.M. Organic Matter, both the medium and the fuel of soil fertility.
It provides the place for all those wonderful soil creatures to live
and the staff they'll consume as they improve and fertilize your
soil.
The one new variation to the chant is that you want to learn to say
"OM" in as many different ways as possible. In other words, the more
ways you can incorporate organic matter into your soil, the better?
OM. #7: Mulch
We've already covered one way to add organic matter to your soil:
mulch. Mulch, along with its weed-smothering, water-retaining, and
soil-cooling virtues, provides an ongoing supply of O.M. to the soil
beneath it as it breaks down. It's a very successful way to build up
soil (Mother Nature uses it all the time), but, well, it is kind of
slow (Mother Nature's never been one to rash). In addition, fresh
mulch (such as fresh sawdust) consumes nitrogen in its first
breakdown stages, so green mulch can temporarily absorb that
nutrient.
All in all, though, adding mulch is definitely a fine way to improve
the organic matter content of your soil. After all, there are those
deep-mulch gardeners (the late Ruth Stout was their patron saint)
who maintain perfectly good gardens by doing nothing more than
continually piling on more and more mulch!
O.M. #2: Crop Rotation
I'm cheating here: crop rotation is not a way to add organic matter
to your garden. The real reason I'm sneaking crop rotation in here
is that it does help balance the fertility in your garden, as well
as reduce plant disease and pest problems ... and both these things
are important for a healthy garden.
(An aside: crop rotation, as the name implies, is generally a
technique associated with vegetable gardens. At least, I haven't
heard anyone talk about flower rotation! Still, if a flower I was
raising in one spot seemed, each year, to get more disease or bug
problems, I'd certainly grow it somewhere else.)
If you let them, crop rotation patterns can get pretty complicated.
Let's keep it simple. First, look at nutrition. Leaf crops generally
need a lot of nitrogen (N), fruit crops generally need a lot of
phosphorous (P), and root crops generally have a fairly high
potassium (K) requirement. (Cole crops, like broccoli, cabbage,
cauliflower, and Brussels sprouts, are treated as leaf crops in this
analysis, like their leafy cousins, kale and collards.) Try not to
plant leaf, fruit, or root crops twice in a row in the same place,
but spread them around so that the same spot in the garden grows a
leaf, fruit, or root no more than once every three growing periods.
Second, let's look at disease and pest prevention. Many diseases are
soil borne and many insect pests over winter in the soil. So if you
move a crop they like to a different area of the garden, it'll be
harder for the bugs (both kinds) to get to that crop next year.
The trick here is to trunk of vegetable families, not just
individual crops. The same pests that bother melons pester their
kin, cucumbers. The critters that nibble cabbage also enjoy a meal
of cauliflower.
O.M. #3: Cover Cropping
Now we get to one of my favorite ways to say OM. Cover crops are a
fascinating and fun way to add organic matter to your soil. They
also have side benefits, such as reducing erosion and even, O
gardener's joy, beating out weeds!
Yet for some unknown reason, I'd say most gardeners don't grow cover
crops! This is a big mistake..
What are cover crops? They are crops grown for the purpose of
improving your soil. Sometimes called green manures, most cover
crops are grown for a few weeks, then turned under into the soil
before they bear seeds or get hard and woody. Used this way, they
directly add a crop of organic matter to the soil. It's like
composting in place, or growing soil!
Cover crops have other uses, as well. Leguminous covers, such as
vetch or clover, have root nodules that fix nitrogen and so provide
extra nitrogen for the next crop grown in that spot. (It's helpful
to inoculate legume seeds with the appropriate rhizoidal bacteria
before you plant it to help its nitrogen-fixing capacity. Just ask
the person who sold you the seed what powder to use and shake the
seed in a bag with the powder before planting.)
Fast- and thick-growing cover, crops like buckwheat or annual rye
can beat out or "smother" weeds, actually eliminating a pesky,
invasive weed. For instance, to rid a flower or vegetable bed of
that pernicious garden nuisance, quackgrass, plant the area thickly
in annual rye as soon as the soil can be worked in the spring. When
the last frost date comes, mow down the rye, till in its roots, and
plant a thick patch of heat-loving buckwheat. Once a month turn the
buckwheat under, and plant more. Then in fall sow winter rye. By the
next spring your plot should be cleansed of persistent weed
troubles! (If this sounds like a lot of work, you haven't been
gardening long enough to know what real work is... namely,
infinitely pulling a perennially persistent weed!)
Cover crops can also be used to over winter J sections of your
garden that otherwise would be open and exposed to erosion for
months at a time. Winter rye, for instance, will start growing in
the fall, and, in most areas, survive winter, then put on a new
spurt of growth in the spring. Or (experiment!) you might grow
annual rye in the fall. In your area it may winterkill and make a
nice in-place mulch for next spring's planting. Or combine either
rye with a hardy vetch, hairy vetch is most popular, which adds
nitrogen to the soil and seems to have other benefits, as well. (A
hot new idea among tomato growers these days is sticking their
tomato plants in a chopped-down but not turned-under bed of over
wintered hairy vetch. Yields have been outstanding.)
All of these uses are in addition to the old, main reason for
growing cover crops: to add green matter to the soil.
So you can see why some gardeners are so excited about cover crops.
Indeed, some C.C. advocates think you should have half of your
garden in cover crops at all times.(I've started doing this myself.
partly because I finally admitted to myself that my garden's been
too danged big!) Others say a third of your garden at any time
should be in cover crops. That's a good goal, too, and certainly to
your garden's benefit.
Your goals don't have to be so grandiose. But, for certain, (1) work
cover crops into your crop rotation scheme. That way, you'll be
rotating not three elements, but four: root, leaf, fruit, and cover
crops. Along with that, (2) plant cover crops any other chance you
get. Start looking for the opportunities and you'll find them.
Cover crops are a cinch to grow. Just work up the soil enough so you
can plant (you don't need to make it super smooth). Broadcast the
seed, sowing thickly by hand, first in one direction and then
perpendicular to it. Then lightly rake over the area to cover the
seed.
The most complicated thing with cover crops is choosing which ones
to use! There're a scillion choices, including a leafy green with
the unfortunate name of rape. No doubt, the queen of green manures
is alfalfa. A deep-rooted nitrogen fixer, alfalfa is perhaps the
most famous soil-building crop of all. But to get real benefit from
it, you need to let it grow for at least a year (you can cut it back
occasionally and compost the cuttings). I don't normally have a
section of my garden that I'm willing to let grow as cover for over
a year, so I haven't yet grown alfalfa... but I'd sure like to.
I can't begin to cover all the cover crops, so I'll just mention the
most popular ones, all of which I've used.
Buckwheat .This champion weed-smothering crop grows so fast you
won't believe it and makes a little grassy field topped by lovely,
small white flowers. Very easy to turn under. Only grows in warm
weather. Not a nitrogen fixer, but great for adding green matter.
Clover. Clovers are as easy to turn under as buckwheat and have the
added advantage of adding N to the soil. White or red are popular
varieties, and seeds are readily available.
Hairy vetch. A graceful, delicate legume with purple flowers, hairy
vetch is quite cold hardy. It can be a little hard to get a thick
stand of it, so it's often grown with a rye (especially winter rye)
to provide more soil cover and give the vetch support
Rye. Annual for spring, winter for over wintering. A great volume of
tall, grassy growth. Winter rye can be mowed as needed the following
spring to keep it under control until you're ready to turn it under.
Soybean. Another nitrogen fixer, one that provides a good leafy soil
cover. Turn it under before it flowers or most of the N value will
go into the seeds.
The real work involved with cover crops (well there had to be some)
comes after they've grown. How do you turn them under? It can be
pretty hard to do by hand. If possible, I like to mow my cover crop
down, it chops die plants into small pieces that turn under easily
and decompose rapidly. Then I till the cuttings and roots under with
my rototiller. If the crop's too big to mow, you can cut it with a
weed eater, swing blade, or (my preference) scythe. Then rake the
cuttings off to compost (thus add to the soil later), and turn under
the roots.
I'd feel a little guilty if I didn't warn you of one thing: winter
rye roots can be pretty danged hard to turn under. The longer the
plants grow, the clumpier the roots get. So, while I used to mow and
let grow my winter rye for as long as possible in spring, I now turn
it under as soon, and as young, as I can.
Also, don't plant vegetables or flowers in a cover-cropped area
until at least three weeks after you turn the cover crop under. It
takes that long for the green matter to begin to break down.
Under-cropping. I can't let this topic go without covering one more,
truly cool way of cover cropping: under cropping. New England garden
expert Eliot Coleman has perfected this idea. Basically, you let the
main crop in an area get a head start in growth, then all around it
(where the weeds like to grow) plant a low-growing cover crop to add
nutrition to the soil while beating back weeds.
The key is: plant your under crop precisely four to five weeks after
your main crop. (Indeed, one hidden advantage to this technique is
it motivates you to keep after small weeds early on so the under
sowing area will be weed free when you plant it.) For short crops,
dwarf white clover is probably the best under sown companion. For
taller ones, sweet clover, vetch, red clover, alsike clover, or even
soybeans will do.
Under cropping is a great way to have your crop and fertilize your
next one, too! Give it a try!
By Valerie Garner
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