Tag Archives: CSA

Physics on the Farm: Brassica in a Whole New Light

At the farm, we gently wash the vegetables in preparation for the distribution. It’s a meditative process: gently we lay the earth bedecked root crops in the first tub of water. Swish, swish! Swish, swish! One can imagine radish tops as the tail of some exotic koi. One by one, each vegetable in turn, passes through a couple of changes of cool water, so that they’re free of clods and are radiant when you pick them up.


One afternoon, while washing the collard greens, John noticed that the leaves took on a silvery sheen when submerged. Green above water, silver below. What was going on? The answer is a combination of botany and physics.

Collard Green leaves (as well as the leaves of other Brassica) are covered with a waxy cuticle, a waxy layer that the plant secretes to deter pests from munching its leaves. The waxy cuticle makes the leaf slightly waterproof and that means air bubbles adhere to the surface when the leaf is plunged under water. (Fire ants take advantage of a similar development in their exoskeletons when they make waterproof rafts of themselves to cross rivers or survive floods … but that’s another story!)

But why would a miniscule layer of air look all silvery? This is where the physics comes in.
Light bends when it travels from one medium to another medium of a different density. In the case of our submerged collard green, from the water into the air bubble on the leaf’s surface. When passing from a more dense (water) to a less dense (air) medium, it is possible for the light to get “trapped” in the bubble and not be refracted back out again. This happens if the angle at which the light enters the less dense medium is greater than 48.6 degrees. At that angle, the light entering the air bubble is reflected off the boundary between the air and the water and does not refract – bend or have it’s speed changed enough to pass back through the boundary. This results in what is called ‘total internal reflection’, and we see a silvery surface. Neat, huh?


For a more detailed explanation of the physics involved see: http://www.physicsclassroom.com/class/refrn/u14l3b.cfm

For more on the fascinating fire ant rafts see: http://www.uvm.edu/~cmplxsys/newsevents/pdfs/2011/ant.pdf



  Skunks are adorable with their thick, glossy coats, dainty hands, liquid black eyes, and inquisitive noses.  How do we know?  We accidentally caught one!

One of our farm managers, John Detwiler, noticed that groundhogs would often make their way along the chicken run’s fence line near the old rowboat that is overturned on the rocks between the concrete wall and the fence.  We’ve been having good luck with catching the groundhogs by placing traps at the mouths of their dens or on the paths they habitually travel, so he thought to put one of the Have a Heart traps there.  One morning, on our way out to the fields, John noticed something in the trap and went to investigate.  His “We caught a skunk!” stopped us all dead in our tracks followed by someone else asking, “So how do you get a skunk out of a trap without getting sprayed?!”  With great trepidation and a lot of ingenuity as it turns out.

Have-a-Heart Traps are tricky.  To release an animal and reset the trap, there’s a lever at the top that needs to be pulled back and held back, a ring that needs to be released from the front, and a flat panel that needs to be shoved forward into the trap until it snaps in place.  Trying to manipulate all three would bring us within squirting distance of the skunk.  Hmmm.  So how do we do all three at a distance?

We first determined that we had to move the trap out farther into the yard.  We threaded a 15 foot piece of PVC through the handle on the top so that two of us could swing the trap away from the fence line and into the yard.  Easy.  Until we realized that a corner of the trap had snagged on a trailing edge of the netting that covers the chicken run.  Jiggling the trap to untangle the netting did little more than rouse the skunk who stood up, arched his back, raised his tail and fixed his earnest gaze on the nearest jiggler.  That put a stop to that!

One of us went into the chicken run to try to pull the netting free.  But as we tugged, we nearly upset the trap (and the skunk!)  We discovered the skunk had begun building a nest by gathering grasses and the netting and dragging them through the steel mesh into the trap.  It seemed a cozy nest, and we were sorry to have disturbed his sleep, but we had to evict him.  After carefully drawing the net back out of the trap, we swung the trap into the yard and hastily covered all but the front of the trap with a tarp.

Whew! We breathed a sigh of relief.  It seems that just like the smaller mammals, we were, on some lower mammalian level of our own, working on the premise  that what you can’t see can’t hurt you.  In this case, it may be true.  We all, the skunk included, seemed a little less tense, and the rescuers could set about their work with less trepidation.

There’s an old maxim, “Always use the right tool for the right job.”  Well, at-a-distance-skunk-releasing-tools aren’t the run of the mill tools we usually have on hand at the farm.  The next best thing is to improvise.  Here’s where the ingenuity comes in.  Ingenuity means standing in the barn and seeing what you have to convert into the right tool for the right job. It means seeing the qualities of something and their application in the broadest context and seeing if those qualities overlap with the qualities needed to address the current issue.  In this case we found:  a 15 foot length of rope, a 10 foot piece of thick wire used to make cover cloth hoops,  a 15 foot piece of 2” bamboo, a garden hoe, and duct tape.  With these handy supplies, we could construct the necessary implements to effect the skunk’s release at a distance.

The metal wire was bent in half to form an open loop at one end; this would be used to pul back the lever.  The hoe was duct taped to the bamboo pole resulting in a 20 foot long lever depressor.  The rope would be attached to the release ring at the front of the cage by some courageous soul .  We all took our places, and after the rope had been attached to the front ring, on the count of three we, yanked, pulled, and pushed and then ran away!

It only took a few moments for our unintentional captive to make a dash for the closest  cover—the old overturned rowboat.  He huddled in the weeds at the base of the wall and extended his clever little paws up and up until he found a section of the wall low enough for him to clamber up and over .  In an instant, he had scurried under the rowboat to safety.

What would we have done had the skunk actually sprayed us?  Applied Skunk Smell Remover.  As it turns out, tomato juice doesn’t actually eliminate skunk odor, it simply disguises it.  Wash off the tomato juice, and the stench of skunk remains!  To be rid of skunk smell, you have to create a chemical reaction that will break the bond between the sulfer molecule in the skunk smell and the oxygen molecule in the proteins that make up whatever has been contaminated.  The following recipe works wonders!  How do we know?  Some of us have had to use it!

 Skunk Smell Remover

 1 qt. of 3% hydrogen peroxide

¼ to ½ cups baking soda

1 – 2 tsp. dish soap

1.   Mix hydrogen peroxide, baking soda and dish soap.

2.   Wet the smelly object or surface with warm water.

3.   Liberally douse the offending object, person, dog, etc. with the Remover.  Rub in  thoroughly.  (Rubber gloves might be a good idea!)

4.  Leave the skunk odor remover on for 5 – 10 minutes so it can set, rinse thoroughly, and then repeat this process as necessary.

It’s important not to store this in a closed container since the mixture of these ingredients creates pressure and could burst.  The solution’s effectiveness also diminishes very rapidly.

The addition of dish soap is important; the soap contains the surfactants that will encase and wash away the smelly molecules that the Remover has released through the breaking of the chemical bond.  Fancy smelling soaps are a bonus!


It’s hot! But no drought … not quite, not yet.

Not us! Not yet.

“Crunchy” is not an adjective that one usually wants to apply to one’s lawn.  But that’s precisely what the grass is this blazing, thirsty July … crunchy.   And yet, according to the weather service, we’re not in a drought.  Well, that all depends on how you define a drought, now doesn’t it?  What’s a drought?

Hydrologic drought is when the groundwater aquifers, reservoirs, and stream flow are below normal. The massive snows of this past winter recharged the aquifers and while the stream flow for the Christiana River is running between the 24th and 74th percentiles (See http://md.water.usgs.gov/surfacewater/streamflow/christina.html ) this is still normal for this time of year on average.  In addition, the large, established trees that rely on subsurface water tables seem in good shape, their leaves full and plentiful. (See http://www.drought.unl.edu/vegdri/VegDRI_Main.htm)  So, accordingly, there’s no drought by these measures, close maybe, but not yet.

A meteorological drought is defined as “a period of abnormally dry weather sufficient to cause a serious hydrological balance.” (Huschke, R.E., ed., 1959, Glossary of meteorology: Boston, American Meteorological Society, 638 p.)  This can be variously defined as an “absolute drought”, a “partial drought”, or a “dry spell”.  An absolute drought is a period of at least 15 consecutive days with less than 0.01 inches of rain or more on any given day. A partial drought is a period of at least 29 consecutive days, the mean daily rainfall of which does not exceed 0.01 inches. A dry spell is a period of at least 15 consecutive days with less than 0.04 inches or more on any given day. If we check the monthly rainfall for June and July, we’ll discover that, meteorologically speaking, we’re not only not in a drought, we’re not even in a dry spell!

But from a farmer’s (or lawn owner’s!)  perspective, it’s quite another thing.  A more recent delineation of the different types of drought includes “agricultural drought”.    Agricultural drought isA climatic excursion involving a shortage of precipitation sufficient to adversely affect crop production or range production.” (Rosenberg, N.J., ed., 1979, Drought in the Great Plains–Research on impacts and strategies: Proceedings of the Workshop on Research in Great Plains Drought Management Strategies, University of Nebraska, Lincoln, March 26-28: Littleton, Colorado, Water Resources Publications, 225 p.) Agricultural drought occurs when there isn’t enough soil moisture to meet the needs of a particular crop at a particular time. Agricultural drought happens after meteorological drought but before hydrological drought. (From: http://www.drought.unl.edu/whatis/define.htm )

Yep. Our crops and your grass have definitely been adversely affected.  Sounds like a drought to me!

For the farmer, the difficulties are threefold:  too much warmth too soon, too little or inconsistent, intermittent rain, and too much sun. Warmer than normal temperatures with abundant rain early in the growing season cause plants to put forth lots of top foliage before they are ready to flower.  If the rain shuts off later in the season as the blossoms are becoming fruits, then the plant struggles to maintain the greenery it initially grew to the detriment of the fruits we look forward to eating.  Warmer than normal temperatures encourage abundant growth, but too much sun, and the tender leaves burn resulting in the loss of entire crops of tender leafy green crops: lettuces, spinaches, etc. and the damaging of newly germinated seedlings.  In fact, sometimes the seeds themselves bake in the too warm soil and never germinate at all.  Rain could to some degree help, but without it, there isn’t much we can do for the seeds already planted. That’s one reason why we do multiple plantings over time of the various crops and have plenty of additional seed on hand.  It’s not a cure-all, but it does mitigate the effects of the drought IF it doesn’t last too long!

So what do we do?  Well, last year we could  water, and did water, sometimes three times a day. The plants were thirsty, and we were glad to do it. Early in the morning, in the evening, and sometimes even in the dark!  With watering cans in hand we walked along the rows, becoming cloudy, indistinct forms after sunset.  There’s something very fairy tale like about watering by moonlight while the deer roam nearby in the hush of the night.

But this year, this crunchy July, we’re giving up our water cans for drip irrigation.  Hooray!  More on that in our next newsletter.

3rd Year Experiment: Trellises

We do a lot of “experimenting” on the farm. What will be more efficient?  What increases the health and productivity of our crops?  What have others tried?  What’s worked or not, and why?  We’re always trying something new (or old, as the case may be with sustainable farming.)

There has been an addition to the landscape at the farm – trellises.  Many plants benefit from trellising: peas, beans, tomatoes, cucumbers, melons, and peppers to name a few.  Any plant with a vine like stalk can be trellised. Trellising is also good for humans; it takes up less room for those with smaller yards and an urge to garden, and it makes picking the fruits a little easier on the knees and back!

Bamboo Trellis

This is our third foray in trellising.  Our first experiment was based on one that we read about in a book by Shepherd Ogden.  He recommended using lengths of bamboo leaned against and tied to each other, to make a sort of elongated tee-pee, with twine tied into a net.  We chose to do this because we had a free supply of bamboo from a friend’s backyard.  We grew beans on these. They were picturesque and worked well until about two-thirds of the way through the season.  The trellises started to collapse because they were rotting through in places.  While wondering why that might happen, we noticed that Mr. Ogden resides in Maine, where the growing season is cooler, dryer, and much shorter – and we live in the middle of a swamp.  As with so many things about farming, moisture is key!

T post and Twine

We used a second variety of trellising for tomatoes last year.  This approach was one that Thera had used on a farm on which she had interned.  In this version, t-posts were spaced every few plants, and twine was tied horizontally between the posts on both sides of the plant to support it by sandwiching it between the strands of twine.  That worked, but required frequent attention: the addition of more twine, the tightening of old twine, and the weaving of errant tomato vines between the strands.

We’re trying this year’s design, which we hope will be an improvement, because it should last for many years, and be much easier to maintain. Each trellis is composed of two 4′ pieces of rebar, two 10′ pieces of ½” EMT electrical conduit, bent into shape, a 5′ piece of ½” EMT electrical conduit, and two set-screw couplings (to join the 5′ piece to the two 10′ pieces), and twine.

As with all new approaches, we sometimes have to learn as we go. To make the trellis frames, we used a conduit bender, a “cut-off saw,” and a metal grinder.  We thought it would be an easy matter to fit the conduit over the rebar, but were frustrated in this when we discovered rebar often has a burr at the point at which it was cut.  About half the pieces of rebar couldn’t be used, and the other half had to have the conduit forced over them.  To respond to this, we borrowed a grinder, to grind the burr off one end of each piece of rebar, and now the conduit fits neatly over just about every piece of rebar.

Two stem, Vertical Twine Trellis

Once the plants are sufficiently mature, a piece of twine will be looped over the plant, wound around the main stem, and tied to the conduit above.  Each plant will be trimmed back to one or two main growing stems which will climb up this single line of twine.  It’s very exciting to see what will result!

For more on how to trellis various types of plants, see: http://www.gardenguides.com/79086-vegetables-can-grown-trellis.html

From E, I , E, I …OH!   the Omnia Humanitas Farm Newsletter

vol 3 issue 2  / June 2011