Crop Rotation

 

crop rotation

Here’s a science lesson, for you…

Our produce contains wonderful nutrients.  We know that.  Vitamins, minerals, and antioxidants are the reasons our parents tell us to eat our vegetables.  Some nutrients are manufactured within the plant, but others cannot be.  Minerals such as iron, selenium, and magnesium are elements: the simplest forms of matter.  From junior high school science, we learned that elements can change form but cannot be created or destroyed.  So, if we eat spinach that’s high in iron, where does that iron come from?  Ok, that answer’s simple… the soil.  Here’s a harder one… If you plant a high-iron crop year after year, will that soil eventually be depleted of its minerals, or does that iron always exist within the soil?  We answered that already by mentioning that elements cannot be created or destroyed.  That supply of iron, selenium, and magnesium needs to be replenished by composting, and the soil needs to get a rest by crop rotation.

Have you planted your crops yet?  If not, read about crop rotation and why it’s important.

Planting your tomatoes in the same place, year after year, can be a bit of a gamble.  If they grew great one year, they’ll grow well the next year, right?  Maybe they’ll get the right amount of sun.  The soil, however, could use a break.  By rotating in other crops, you avoid disease and insects, and you replenish nutrients.

Replenishing Minerals

While plants can create some vitamins within their cells, the minerals must come from somewhere.  Those minerals include magnesium, potassium, calcium, iron, zinc, and selenium, among others, which are essential to our health.  Other elements, such as nitrogen, may not benefit us as much as they benefit the growth of the plant.  Chemical fertilizers replenish only a few of these nutrients, mainly nitrogen, potassium, and phosphorus.  By composting, you place those minerals back in the soil.  By rotating crops, you grow a food that takes different minerals instead of depleting the same ones.

Primary nutrients in Miracle Gro: nitrogen, potassium, phosphorus
Primary nutrients in Miracle Gro: nitrogen, potassium, phosphorus

Avoiding  Insects

Last year, squash bugs hit me hard.  I planted a stretch of land that had not been gardened for at least ten years.  I grew zucchini, pumpkins, and three types of winter squash… a buffet for squash bugs.  Thankfully, they hit during the end of the growing season and my squash had matured before the vines started to die.  Ugly creatures that look like gray shields, these insects resist pesticides.  My chickens wouldn’t eat them.  Gardeners advise two ways of controlling squash bugs: squash them with your fingers whenever you find them (ick) and avoid growing squash.  After about three years without squash, the bugs have starved off.  But if the garden had not been cultivated for at least ten years, where did the squash bugs come from?  They swarmed in from all the other gardens in the neighborhood.  And since they swarmed in with such force, onto a stretch of land that had no way of supporting the bugs before I planted, I know they’ll be worse next year.  If I plant squash in that garden for the next few years, I’ll be pulling my hair out as I rip off leaves and squish eggs.  So we’ll just plant the squash in a completely different garden.

Squash bugs
Squash bugs

(Photo credit: http://www1.extension.umn.edu/garden/insects/find/squash-bugs/)

The same rule can apply to tomato hornworms, earwigs, potato bugs, and many other insects that target specific plants.  If you have an insect infestation that prefers a specific crop, the easiest way to overcome that is to grow a completely different variety of plant in that area for a few years.

Avoid Disease

In Reno, we don’t have as many problems with blight that other areas do.  This is primarily because we don’t have the moisture that other areas have, and because we don’t have many swaths of land cultivating a specific type of food.  Blights can be devastating in places like Idaho, where the same fields are used year after year for the exact same crop.  If you need a little anecdote about blight, read back about the Irish Potato Famine and the need for genetic diversity.

Late blight in early stages
Late blight in early stages

(Photo credit: http://stoneheadcroft.com/2008/08/20/potato-blight-hits-hard/)

But blight isn’t a moisture problem.  It’s a mold problem.  No matter how wet your garden is, mold doesn’t just appear.  It comes from spores, which, like bugs, have to originate somewhere.  It is possible to get blight in your potatoes during the end of the season, and not know you did, because the die-back stage of potato cultivation looks very similar to late blight.  Growing potatoes in the same soil, the next year, would guarantee those potatoes would suffer from the blight.  Even worse, blight affects other plants in the nightshade family: tomatoes, peppers, and eggplant.  Though you can avoid many fungal problems by controlling the moisture in your garden, it can be devastating when it’s there.

Perfectly healthy potatoes, nearly ready to harvest
Perfectly healthy potatoes, nearly ready to harvest

Other diseases that can be plant-specific are leaf spots, scabs, wilts, rots, mildews, smuts, and viruses.  Though a few of these diseases can cross to another plant genus, most stay within a specific type.  Blights and fungal wilts often affect tomatoes… and potatoes, peppers, and eggplant.  Another kind of damping off affects beans.  Specific downy mildews and black rots affect crucifers (broccoli and cauliflower.)

Nurseries and greenhouses carry expensive sprays or powders, which can combat many of these diseases if you do happen to get them.  Avoiding them, though, is exactly the same as avoiding bugs: rotate the crops.

Crop-Rotation is an ages-old concept.

Before commercial fertilizers and pesticides, farmers rotated their crops.  This occurred as early as Roman times and in ancient Asia.  In medieval times, farmers had three fields: one of winter wheat or rye, one of peas or beans, and the other lay fallow (unplanted).  This provided for the different nutritional needs of the people while removing/replenishing different nutrients and allowing the soil to rest for a season.  In the southern United States, George Washington Carver taught farmers to rotate soil-depleting crops like cotton with soil-enriching crops like peanuts or peas.  Today, organic farmers rotate their crops to avoid use of pesticides and commercial fertilizers.

How do I rotate my crops?

First, figure out what families your crops belong to.

  • Nightshades: tomatoes, potatoes, eggplant, peppers
  • Curcubits: squash, pumpkins, cucumbers, melon
  • Brassicas: broccoli, cauliflower, Brussels sprouts, cabbage
  • Legumes: beans (bush and pole), peas, lentils
  • Alliums: onions, garlic, chives, shallots
  • Root crops: carrots, beets,  parsnips, turnips
  • Grains: wheat, rye, oats, barley, corn

Second, switch up your garden plan.  Simple enough.  If you planted tomatoes in a specific spot last year, do not plant tomatoes, eggplant, peppers, or potatoes in that spot this year.

Third, consider nutrient replenishment.  Legumes are crucial for fixing nitrogen in the soil.  This can be extremely beneficial after growing a soil-taxing crop like corn.  Last year, I planted potatoes down the length of my garden.  Different crops bumped up against the potatoes.  At the end of the year, I harvested the most potatoes from the plants beside the beans.  Though the benefits of nitrogen fixing normally affect the next year’s crop, the close proximity had already benefited the current year’s potatoes.

Garden #2, on July 25, 2012
Garden #2, on July 25, 2012

My crop rotation schedule always involves a 3-year cycle of nightshades, beans, and something else.  That “something else” can be onions, root crops, squash… whatever.  It all depends on the pests in the area, the amount of sunlight, or my family’s food needs.  Whichever it is, though, I make sure I have “something else” within my 3-year rotation.  Last year, I grew eggplant in my front planter bed, so this year I’ll grow Jacob’s Cattle beans.  The sidewalk bed, which has had squash and potatoes in previous years, now holds onions and Swiss chard.

Do you have any success or horror stories regarding crop rotation, or maybe regarding bugs or disease?  I’d love to hear them.

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