By: Richard de Wilde
“What we call a weed is in fact merely a plant growing where we do not
want it.”
—E.J.
Salisbury, The Living Garden, 1935
Leeks after cultivation using "The Lilliston" |
As organic farmers we do our best
to understand and work with the natural world.
Nature is wise and knows the value of keeping soil in place and covered
with plants which maximize each day of sunshine, capturing carbon and nitrogen
from the air while exhaling oxygen that we need to live. In nature, soil is never left bare to be
wasted or eroded by wind and water. Weeds
have a purpose, and it really is a good one!
So why are we so set on killing and eradicating them from our
fields? Weeds can be very aggressive and
can inhibit the potential of a crop by competing for sunlight and
nutrients. They impede our harvest
efficiency and produce thousands of seeds which will haunt us for years. Most weeds have accompanied agriculture from
its beginning. They moved around the
world as early settlers brought their grain seed along with some tag along weed
seeds and today they hitchhike with the global grain trade and then further
spread by way of wind, animals, equipment, etc.
Potato field cultivated with "The Lilliston" |
Weed plants are very adaptive. They can lie dormant in soils for 10-30
years, just waiting for their time of need to germinate. Some weed seeds only germinate at certain times of the year,
such as in cool spring or fall temperatures.
Others are triggered in times of excess moisture, while others only
germinate in summer heat or extreme drought.
Weed seeds are also triggered to geminate by exposure to light, usually
caused by tillage. Tillage is any
disruption of the soil, which in our case could be cultivation or other work to
prepare the soil for planting. As the
soil is stirred and disrupted, even just a flash of sunlight is enough to
trigger some weeds to germinate! In
fact, I’ve read that in Europe some farmers even started cultivating at night
to avoid triggering weed seeds! Weed
seeds may also be triggered by fertility needs in the soil. Some weeds have the ability to correct soil nutrient
deficiencies. For example, if soil is
deficient in phosphorus, a seed for a plant that has the ability to scavenge
phosphorus may be triggered to germinate and grow. As we try to minimize weeds in our crop, one
thing we do is to provide balanced nutritional needs for the soil to prevent the
need for weeds to correct the deficiency.
Cilantro: Cultivated with "Basket Weeder" with shields & Kult Kress Duo. |
There are really only two kinds of
weeds, annual or bi-annual weeds and perennial weeds. Annual or bi-annual weeds grow rapidly from
seed, but only under the right conditions.
In order to thrive once they germinate, they need to grow and develop their
green structures above ground to capture sunlight and utilize photosynthesis
for energy. When these types of weeds
die at the end of the season, they are dead and won’t grow again. Thus their main way to propagate themselves
is to produce seeds that drop back into the soil and are available for a future
season. In contrast, perennial weeds
survive from year to year and their main strength and the key to their survival
is their underground root storage system which holds nutrients and energy. When a new year rolls around, they don’t have
to wait for the right conditions to germinate a seed and start
photosynthesizing, rather they draw their energy from their roots. The key to eradicating these types of weeds
is depleting their root reserves. Up
until the plant is six inches tall, it is drawing its energy from its root reserves. When it is about six inches tall, it starts
utilizing photosynthesis to put energy back into the roots and replete the
reserve. One way we can battle this type
of weed is to repeatedly mow it off when it is about six inches tall. This
takes persistence, but after time the root reserves will be depleted and the
plant will die.
Rafael using disc cultivator in the cilantro field. |
By now you may be wondering if
there is a silver bullet for weed control.
Valid question and one farmers have been asking for years. In a recent article in Acres U.S.A. written by Anneliese Abbott, she commented about the
onset of agricultural herbicide use. “It
seemed so easy: forget about plowing…and
just spray chemicals to kill the weeds.
No tillage, no erosion and no weeds:
what could be better?
Unfortunately, herbicides caused as many problems as they solved. They
polluted water, harmed non-target organisms and sometimes posed a threat to
human health. Worst of all, they only
worked well for a short period of time.
Weeds quickly evolved resistance to every major type of herbicide,
forcing farmers to spray more and more chemicals with less and less success
every year.” Sadly, as organic farmers there is no easy way
to deal with weeds. Rather we try to
understand how weeds work, the conditions they thrive in, and then we utilize
multiple methods to kill them and prevent their growth. Aside from the occasional use of 30% vinegar,
chemicals are not our answer. So lets
talk about the methods and tools we can use.
New weed control technique: Low growing cover crops between rows of melons. |
One of our weed control tools is
planting cover crops of grains, grasses and clovers. If we can satisfy the need to cover the soil,
there’s no need for dormant weed seeds to germinate. It helps that most grasses and cereal grains,
such as rye, also exude chemicals to inhibit other seeds from germinating. Historically we have planted most of our
cover crops in the fall, which can serve to prevent the growth of bi-annual
weeds. Bi-annual weeds germinate in fall,
but do their growing in the spring. If
we can inhibit germination with a fall cover crop planting, we won’t have those
weeds in our spring planted crop. We are
also perfecting a new and exciting technique we’ve developed for controlling
weeds that grow in the space between the beds where crops are planted. Immediately after preparing the beds, we plant
two very fast germinating cover crop plants, creeping red fescue and white
Dutch clover. Both grow fast and inhibit
weeds. They are also short in stature,
only 6 inches tall at most, so they do not compete with our crop for sunshine.
Using Flame Weeder to kill small weeds before crop emerges |
We can also deplete the “weed seed
bank” in the soil by triggering weeds to germinate, then killing them when they
are small with very shallow cultivation or flaming. We typically utilize this method before we
plant the crop, but it requires us to prepare the beds one week ahead of
planting. Then, just before we plant, we
“basket” the beds. A “Basket Weeder” is
an implement mounted on a small tractor.
It has horizontal wires that flip small weeds out as they roll across
the surface of the bed. We can also
utilize a “Flame Weeder” to kill weeds that germinate and emerge after the crop
has been planted, but before it comes up.
In order for this to work, the timing and conditions have to be just
right. The flame weeder is a tank of
propane mounted on the back of the tractor with burners that carry just over
the surface of the bed. The flames burn
the weeds off, thereby killing them. If
you flame too soon, you won’t maximize the number of weeds you kill. If you wait too long, the crop may start to
emerge and you risk burning off your crop.
We utilize flame weeding for crops such as cilantro and dill that we
plant every week for over twenty weeks.
Typically we have to time the flaming about 4-8 days after the crop is
planted, depending on temperature. We
also use this technique on carrots and parsnips and the difference between a
crop that has been flamed and one that has not is dramatic!! We have a significant reduction in weeds with
timely flaming. When we do get weeds in
our field, it is critical that “bad” weeds to go to seed in the field or areas
around our fields. If they do, they’ll
make a deposit into the “weed seed bank” that we’ll pay for in years to
come!
Vicente using "The Lilliston" to "hill" sweet corn |
We have a few more tools in our
collection of things for weed control. Sometimes
we use a tool called “The Lilliston” which aggressively throws dirt in one
direction and can be used to smother weeds by throwing dirt on them. We use this to smother weeds within the rows
of crops such as potatoes, leeks and sunchokes when the plants are big enough
to get partially covered by dirt without damaging them. Another tool we use is called a “Lely Tine
Weeder.” This tool has little tines that
rake out very small weeds. This is a
more gentle tool and can be used on small transplants and fast growing crops
that are direct seeded, as long as the crop is larger than the weeds. The “Basket Weeder” is also extensively used
with tunnel shields that we put on the implement to carry over the rows of
crops to protect them from dirt flying into the row and smothering the crop
when the crop is too small. While this
method preserves the crop and kills weeds in between the rows, it doesn’t do
anything to remove weeds that are in the row.
Later, when the crop is bigger and can take a little more aggressive
cultivation, we remove the shields.
Jaime and Felix G using "The Kult" in celeriac |
In more recent years we’ve started
using a steerable cultivator that we call “The Kult.” It requires a team of two people to operate
it. One person drives the tractor and
the other rides on the cultivator to steer the machine. This tool is more effective at killing weeds
within the rows of crops and it is indispensable at killing new weeds in larger, more
established crops where we have to be careful not to disturb the crop’s root
system or damage the plants. It’s also
adaptable and can be set up in a variety of ways to best meet our needs. We have even more cultivating tools, but I
think you can see we try to utilize mechanical options as they are our most
efficient and cost-effective means of killing weeds.
Ascension using a hoe and his hands to remove weeds in the strawberry field |
We can also smother weeds by
covering the soil with plastic or straw mulch.
Some of our crops are planted on plastic covered beds. We use the plastic mulch for a variety of
reasons, one being weed control. As a
last resort, when we’ve exhausted all other methods, we turn to old-fashioned
hand weeding. Yes, we do still do more
than our fair share of hand weeding and this too is a skill. We try to avoid weeding by hand because it is
time consuming, but sometimes that’s the only option.
Will we ever kill all the weeds in
our fields? No, but the sum total of all
our efforts will pay off this year and in years to come as we minimize the
impact weeds have on our crops.
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