Saturday, January 15, 2011

Drifting Through Winter

When planning layout and design for the placement of a landscape in a zone where winter brings wind and snow it is possible to make your winter easier by saving  time and effort shoveling and have the added benefit of directing moisture directly to the plants that need them  through what I call "perennial drift control".

In order to understand the basics of how this system works it might be helpful for me to define a few terms and explain how snow drifts.  Some people will find that they may have never paid much attention to the details of exactly how snow drifts but with a little practice and an understanding of some aerodynamic principles you will be able to create your own solutions for drifting snow so that this valuable water resource is used to it's highest potential.

The first two important terms are "windward," and "leeward."  Those of you who have sailed before will know these words well, but let me go ahead and give the brief explanation.  Windward is the word used to designate the side of an object that is facing directly into the oncoming wind as illustrated below.  This will change depending on the direction of wind in your location but here in Greeley the wind almost always is a westerly (originating in the west blowing toward the east).  This piece of information is very important to observe and to gather data on because this is how you will build your perennial drift control.

Leeward is the term used to designate the side of an object shielded from the wind.  In the above drawing the leeward side of a wall creates a pocket of slower more turbulent air.

My yard has a very peculiar orientation in relation to the average direction of incoming winds.  The neighborhood is aligned in a  way that westerly winds blow directly down the street in the front of my house and are funneled into MY front yard which sits at a bend in the road.  This bend has the effect of creating wind vertices that my son lovingly refers to as the "trash vortex".  What essentially happens is that all debris picked up from civilization West of my home gets swept down the funnel into a swirling turbulence of winds that place the materials directly into my NE window well.  I am not exaggerating when I tell you that I have had the pleasure of cleaning everything from unopened mail to a child's plastic swimming pool from my NE window well (the wind actually folded it and crammed it down into the window well cavity.)

What is it that makes the Trash Vortex relevant to drift control?  Well the very same effect that carries trash into my window well also carries vast quantities of snow into my driveway, yard, and yes...window well. The solution lies in not stopping snow but instead creating a drift that is where we want it to use the moisture from the snow where it is needed and to leave pathways, driveways, gates, and doors as clear as possible from snow drifts.

This strategy actually assists with a more natural aesthetic placement of plants.  The result is a beautiful yard however, the placement of that new serviceberry will not be in a Victorian style hedgerow.  What you will have is a naturalized space with good use of a three story layering which makes shoveling easier and your trees healthier.

The first step is to notice where snow already drifts in your yard and make an evaluation of whether the drifts are:
1. In the way.
2. Currently the result of another plant initiating the drift.
3. Providing moisture to a perennial.
4. Causing structural concerns to a home, barn, shed, open garage.
5. A high drift settling in from the top of a hill, mountain, or building.

In the case of the fifth descriptor, there is really nothing that can be done to redirect the snow. The snow is slowing as the wind is blocked by the object such as a building and will inevitably settle in these spots.  This problem will create a heavier build up and a dome shaped drift in the leeward side of the object. Look at the illustration below.  This situation can be used to your advantage by planting a deciduous perennial (fruiting) shrub or tree square in the middle of where the drift occurs.  The result is that melting snow will provide slow soak moisture to the perennial. The amount of moisture will be roughly about one inch of water for every ten inches of snow depth.

In the case of the first and fourth descriptors you will want to prioritize your next plantings to fix the problem.  A drift that crosses a sidewalk or driveway can be greatly reduced by planting low growing dense hedges or shrubs such as Nanking Cherry or a Hazelnut bush windward of the path or  structure to slow the driving snow so that the drift shadows the shrubs instead of advancing onto the pathway.  Cold hardy clumps of bamboo can augment the shrubbery as well as pampas grasses.  The grasses are not edible but make good companion plants for the edible shrubs if planted windward of them to reduce dessication from driving winter winds.  These can also be used to cause drifting before the wind drives snow against a structure.

One of the most interesting uses of perennial drift control is to direct moisture where it is needed.  Causing large piles of snow to accumulate at the leaf-line of a tree or pile up around fruiting shrubs is actually a pretty easy process and can be accomplished in a variety of creative ways. Primarily what you want to do is to slow the air.  Use perennial fruiting shrubs, and strategically placed boulders.  Place them on the windward side of the place that you want drifting to occur.  The only other consideration is distance.  Remember that the distance should allow for the snow to build up in a place that stores snow for use as it melts.

This technique requires some long term observation and perhaps pictures or note taking as the winter months happen.  If you consider your placement with this variable in mind you will save time, money and plants next winter.

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