To Coir or not to Coir

Few things seem to get hop growers worked up more than what they use to train their hops.  At the heart of the issue is mostly opinion but we should ask some hard questions about what we should be using for our yards.  

I thought long and hard about why we use coir twine in our operation when there are many other options.  It all came down what works best for our yard.

Tensile Strength

Tensile strength is a measure of how much force the “string” material can withstand safely or before failing.  Ratings are given in pounds-force (lbs/f) or in pounds per square inch (psi).
They are both similar BUT remember that is the rating is in PSI the number must be derated for the cross-section of the string.   See my post on PSI vs Lb-F for more info.


Hop growers have 3 materials from which to choose when stringing the yard; natural fiber, synthetic fiber, metal wire.  Natural fibers are wide-ranging but most popular are coir (coconut fiber), sisal (grass), and twisted paper.  Hemp is also an option but in the US it is prohibitively expensive for large scale operations.  Synthetic fiber string is typically polypropylene baling twine but can include any polymer twine but price usually restricts their use.  Finally metal wire is a traditional material used in some European regions but is rapidly being replaced by natural fiber due to food safety issues.


In the hop yard we need our string to last the season but then be compostable after harvest.  Not an easy task for sure but considering a few attributes can help with deciding on the right material for you.

Coir and sisal are both semi-resistant to single season rot and seasonal longevity is heavily dependent on the thickness of the strand.  All things being equal a string of the same diameter will have near equal rot resistance.  Coir fiber is approximately 60% less expensive than sisal so the thicker coir twine will have more fibers to sacrifice to microbes than the typically much thinner sisal.

And then there is paper.  A relative newcomer twister paper is not particularly rot resistant by itself.  It is used extensively in the Northwest US where growers soak the soil end of the twine in a mixture of diesel fuel and copper preservative to make it last the season.  It seems to serve the purpose for those growers although it is a bit more expensive than coir.  Manufactured domestically means shipping is less.

Metal wire and synthetics are also options but each cone with serious issues.  Metal wire is cheap but unless you’re willing to run it through your harvester and deal with magnetic separation then I’d stay away from it.

Some brewers will not accept hops grown on wire just because of the implied risk of contamination.  As a processor I will not accept bales that were strung on wire.  Synthetic twine as come a long way in the last decade.  Most of this twine is polypropylene and made for baling hay and straw.  It’s available in various strengths and quite inexpensive.

However consider what you have to deal with after harvest.  Our Wolf harvester chops up the bine and twine and a conveyor takes it outside.  Unless you buy the biodegradable poly twine you’ve got a big pile of uncompostable hop debris.


Equally divisive is the topic of twine fastening.  Obviously tying twine at the top is standard but how about the bottom?

Some growers have a suspended drip line to which they tie the bottom of the twine.  Some growers have heavier soil so they can simply stab the twine into the soil.

On light soil a special metal clip is pressed into the ground along with the twine.  In some European yards the grower installs stakes at each plant and use continuous wire or sisal twine.

My Decision

I’m on Team Coir.  I have heavier soil so I fan jam the twine into the ground without using clips.  We tend to have regular rainfall and we drip irrigate so using lighter sisal twine is not an option.  It rots in weeks and I lose all stability and broken bines result.

Buying in volume drops the coir price to the point where other materials are nor competitive.  Poly twine is right out; even the biodegradable stuff.  It wraps around my harvester  chopper and melts into the bearings.  And something about soaking paper in diesel and putting it into the soil bothers me.

Your results may vary.


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