- Author: Jenni Dodini
Well, after turning in my last blog, Jennifer (UCCE Master Gardener Program Coordinator) asked, "What scientific research did you find to support corks helping keep moisture in the soil?" There really wasn't any when I did my blog. I think that I got carried away by all the pictures. Then I focused on the wood mulch that is bad for the plants and how that was wrong. Then it really got to bothering me that I had not followed my own advice and "do your research," so after the fact, I went and did my research. This is what I found, and it was not that easy. I ended up on these sites: OrganicAuthority, Smithsonian, GardeningKnowHow, and Univ. of Washington/Elizabeth C. Miller Library/ Gardening Answers Knowledge Base. They were the only ones with actual information.
Quercus suber, or Oak cork tree, is primarily native to Spain, Portugal, and the Mediterranean.
The corks that we know come from the bark of the tree and as most barks, contain Suberin "which is a waxy, hydrophobic substance." As with other barks, it repels water rather than holding onto it. The inner tree wood does not contain Suberin. The average cork tree lives about 150 years and is of ecological importance to the animals and the financial livelihood of the people in the areas where it grows. The bark is stripped from the trees once every 9 to 12 years and takes that long to grow back. The stripping process does not harm the trees. The average tree produces about 100 lbs of cork per stripping. One ton of the bark yields about 100,000 corks! Cork takes a REALLY long time to decompose unless minced up. I couldn't find any information on any nutrition it provides though.
So, what was my take away here? The corks in the bottom of a pot will help promote drainage. Corks in the top of the pot or on the surface of the soil will help lock in moisture, the same as any other mulch. And, DON'T FORGET TO DO YOUR RESEARCH!