Friday, March 6, 2015

HIVES MADE OF CEDAR? (by beekeeper Fred)

Since the advent of varroa and tracheal mites there has been a flood of ideas on how to increase hive survival; some good, some bad and some totaling ineffective.  Several suppliers are promoting hives made of cedar instead of the traditional red or white pine as a means of increasing hive survival.  Whether this is simply commercial promotion or hard facts is for you to decide.  

Several benefits are purported by a change to cedar. 

1)  Cedar has a lower coefficient of thermal conductivity.  0.053 for cedar versus 0.060 for pine.  For hive sides of the same thickness this means the cedar hive would transfer 10% less heat from the inside of the hive wall to the outside.  Whether this results in the bees needing to generate 10% less heat to stay warm is debatable.  Remember there is still the cold air void surrounding the bee cluster inside the hive along with several layers of comb and honey.  In addition there are usually a lower entrance and an upper vent to encourage a slow airflow through the hive to void it of a moisture build up.

2)  Cedar has a lower density than pine.  If a constant brood box weight were maintained the brood box wall thickness could be increased by roughly 25% or the wall thickness could be increased from the current ¾ inches to roughly 1 inch.  This would further insulate the hive. 

3)  Cedar wood has aromatic oils in its pores.  Cedar oil is attributed with antibacterial and pesticidal benefits.  In the supplier literature these benefits are talked up.  But the literature doesn’t provide any scientific data affirming these benefits; such as cedar oil has been proven to kill 99% traecheal mites and 75% of varroa mites.
Therefore I can confirm hive boxes made of cedar will transfer less heat from inside to outside in the winter.  Conversely, it will also transfer less heat in the summer, requiring the bees to dedicate more effort to the task of ventilating the hive. 

I haven’t seen anything written that is negative about hive boxes made of cedar.  The strength of various types of cedar and pine woods is similar.  Although tensile and shear strength of cedar is slightly less than pine, the difference would not be considered significant considering the types of mechanical loading to which the hive boxes are subjected.   Cedar lumber does cost more the pine lumber and I would expect this to be reflected in the cost of cedar hive boxes.  
Other insulating methods such as Styrofoam or insulation wraps can also cut heat loss.  These methods have been in use for years and the debate over whether the extra insulation is beneficial is still being debated.

I haven’t seen any scientific literature that cedar boxes increase hive survival.  I have been in the bee game only a short time and may have missed this data.  If you have seen any data to the contrary please let me know and I will amend this write up.  That said here are two sources for woodenware made from cedar.  Their websites have some thought provoking write-ups.  Read and enjoy.  Makes 8 frame hives with 1 inch wall thickness   Makes several different styles of cedar hives. 

Remember the East Central Wisconsin Beekeepers Club does NOT endorse any supplier’s products. 


d said...

and what do you "see" people treating the outside of the boxes with? are they painting or staining or clear coating or parafin/wax dipping?....or leaving them to weather untreated? i could see some benefit to the benefit of exposure to the cedar oils (just like the old cedar closet against moths idea)....which leads me to wonder about MOTHS getting into...OR NOT WANTING to go into cedar hives. hmmm? I NEED TO TRY ONE OF THESE - get hubby down to the store for some cedar!

Fred Ransome said...

Cedar, if left unpainted, tends to last longer than unpainted pine. Over time it will probably turn the same washed out grey color as pine. If you want to preserve the "cedar" color will probably require periodic application of a varnish or clear coat. I have a few varnished pine hives in my apiary. Interchanging of equipment (one white box and one varnished box) does look a little odd.

From a scientific standpoint "trying one of these" is not not a good experiment. Do you have two hives with moths so you could g=properly gauge the benefits of cedar?

You could simply send him out to buy some cedar oil and wet down the bottom board. Better yet, I have a pint bottle of red cedar oil spray leftover from when I made several cedar chests and will provide you with a small bottle if you agree to run a side by side test.