Some of you may be familiar with Prunus laurocerasus, English Laurel. You know, that merciless shrub most often used as an intimidating hedge that will take over your garden, your garden art, your garden furniture, and your dog if he sleeps in one spot too long. The plant that will quickly grow into an impenetrable wall of green 12 feet tall if your neighbor doesn’t trim his side of it (no matter how nicely you ask, or even if offer to trim it yourself). Yes, that plant. I know this plant well because it resides in that inscrutable, flexible zone called our Property Line. This plant doesn’t get along well with the other plants in the garden it borders. Nothing grows under this hedge, and not because of shade. I have carved out small full-sun spaces at its base with the intent of using those areas for small sun perennials. No luck. The perennials don’t even survive a year. Bind weed (Convolvulus arvensis) grows into and through laurel’s multiple, sturdy stems but, apparently, not under it. Even dandelion, the plant of the century, stays clear of the hedge. The only plant I have seen that grows in concert with English Laurel is Hedera helix, English Ivy. Hmm. . . .
Anyway, this made me wonder if laurel might be allelopathic. Think of the possibilities! I may have found a never-ending supply of weed killer/suppressant right outside my front door. Think of the savings – both time and money! I could take my new discovery “on the road”, going door to door offering laurel boughs to any neighbor brave or foolish enough to give my idea a try. With many possibilities rolling around in my mind, I tried 4 experiments here in my garden (I have a few weeds to sacrifice). Beginning with a dandelion, I covered the healthy, thriving weed with laurel leaves and left it alone for 3 days. On the morning of the 4th day, I uncovered the dandelion and found a wilted plant showing signs of initial desiccation, but still alive. Struggling, suffering, but not dead yet. (Sounds cruel, I know.) The laurel leaves were as green as ever but just beginning to show signs of curl. More time was needed, so I covered the dandelion with new laurel leaves and gave the experiment 2 additional days, checking the plant once each morning. On the morning of the 7th day, I found a very dead weed. And I was very happy. Duration of this experiment was 6 full days.
The dandelion had been growing in full sun during a stretch of 90+˚F days with, of course, no water. For the next experiment I chose a partial-sun location with a small amount of young petty spurge (Euphorbia peplus). This experiment included a stretch of days over 85˚ with one day at 92˚, again, with no water. I left the site alone for 3 days, and began checking the plants daily on the morning of the 4th day. By afternoon of the 5th day, all herbaceous growth was dead. Duration of this experiment was 4.5 days. The site remains uncovered and after 3 weeks no new spurge is seen.
The next plant I chose to experiment with was herb robert (Geranium robertianum). This experiment consisted of one young plant six inches across, growing in full sun. This plant was an easy kill – by the 4th morning (the first time I checked it) the plant appeared thoroughly dead. I uncovered it and left it in place for 2 weeks. It’s still dead.
My last experiment – bind weed (Convolvulus arvensis) – was a quick failure. The bind weed grew out from under its heavy cover of laurel leaves with a strong, healthy shoot in the short duration of 3 hot, sunny days. Didn’t even slow it down. This one will require much more time and thought.
This is just the beginning of the hard work I have planned for Prunus laurocerasus. For such a nuisance plant – one I inherited and one that my neighbor (bless his heart) loves so much he won’t prune – there may be some redeeming qualities, after all. And those qualities may not reside only in the roots, but in the leaves as well. Or, it could be that the leaves are so tough and leathery that they suffocate most plant material they fall upon.
I’ll keep you posted.