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| My last post missed the mark, although Kmmsr was kind enough to respond. My husband is convinced that I am killing my soil by using pine needles as a winter mulch in my raised vegetable gardens. I will, of course, remove it before planting in spring.
Pine needles contain terpene which prohibits germination of seeds (http://www.helpfulgardener.com/phpBB2/viewtopic.php?t=1860). Nitrogen in compost can break down terpene, but I would like to know if anyone has found vegetable seeds sprout poorly after mulching with pine straw. .
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Here is a link that might be useful: Terpene
Follow-Up Postings:
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| zuni, pine straw has long been used to prevent seed germination. It's an allelopathic property, rather than physical. For that reason, pine straw is terrific in ornamental beds, around trees, etc., but not so good in the veggie garden until AFTER the seeds have germinated and the plants are growing. HOWEVER, different pine species have various allelopathic properties. What kind of pine are you talking about? Also, I have doubts that any seed inhibition chemical would remain in the soil if you remove the pine straw, as you said. |
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| Rhizo_1, THANK YOU for clarifying that! No one seems to mention the allelopathic properties of pine mulch. I do not know what type of pine it is. The needles are from a relative's cottage. I'm using only about 1/4 inch of needles as mulch, and plant to remove it before planting. My hope is that it will provide a little extra acidity, and protect the soil thru the winter. |
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| Allelopathy is still pretty mysterious, even to the scientists who are studying it. If it were talked about a lot more in the professional arena, a LOT of landscape and turf issues would be solved very simply. |
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- Posted by toxcrusadr (My Page) on Wed, Oct 12, 11 at 14:44
| Interesting topic that I was not aware of. I don't have any details to offer, other than the fact that terpenes are relatively volatile, not to mention biodegradable, and shouldn't hang around long after the source (needles) is removed. That's strictly my chemistry background talking though. Actual fact may differ. Terpenes are a class of hydrocarbons similar to many found in gasoline or (obviously) paint thinner. |
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| I wouldn't expect anything measurable in the way acidification, Zuni. Many believe that pine needles/straw are preferable over other organic matter for lowering soil pH. The thinking goes, that because the soil under pine trees is usually acidic it was caused by the blanket of needles. The fact is that pine usually favors acidic soils in the first place because the acidity makes certain nutrients more readily available to pines. If the soil was less acidic, the pines would likely have been out-competed by stronger growers and they wouldn't be there. So if you're concerned about allelopathy, substitute other available organic matter. The following is something I offered in another discussion on another forum. It's a little off the mark because it was written to forewarn about the impact they might have in container media, but you might find something worthwhile in it: .... I'm sort of neutral about pine needles in compost and as mulch - nothing particularly special about it for lowering pH, and pine needles ARE high in terpenes and aqueous methanol, both substances KNOWN to be allelopathic (inhibit growth of other plants), so I would probably question the wisdom of including them in container media and leave them out entirely ..... but that's just me. ;o) Spreading an inch or two of mulch over thousands of sq ft of mineral soil wouldn't have nearly the impact as it would if you made them a notable fraction of your container soil. The organic compounds mentioned are volatile and do tend to dissipate as the needles age, so if the pine needles no longer SMELL like pine needles, there would be a much reduced concern about allelopathy; but the terpenes and other bio compounds are what inhibit decomposition, so by the time the affects of allelopathy are diminished, the needles are at a point where they can be counted on to break down quickly. Al
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| That explains my failed cabbage this past year. Great to know for using where you don't want weeds. I wish they sold it here up north. I can only get what is dumped in fall. I get white pine here, not as tough as the southern pines needles, but works okay. |
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