Barrier Garden

Recently I’ve been working on a new garden. It’s at the edge of the house paddock, between the olive trees and the boundary fence. We want to turn this area into a “barrier garden” between the main vegetable beds and the rampant kikuyu grass in our neighbour’s pasture. The area faces into the sun, so despite its proximity to the olive trees, I think it will get plenty of light.

Bill Mollison’s Introduction to Permaculture discusses the use of plant barriers to keep invasive plants like kikuyu out of gardens. In particular, he suggests comfrey and lemon grass as good barrier plants against kikuyu. Inspired by these suggestions, I started a whole lot of lemon grass from seed recently, and have planted a line of it along the fence at the back of the barrier garden. The rest of the barrier bed will be taken up with other useful herbs that we’d like to grow, but which are rather too large and/or rampant to put in beds closer to the house. These plants include:

lemon balm
tansy (too invasive to plant in the main garden, but must have it in the garden as it’s very useful for de-worming the goats)
willow herb

I’ve planted annuals, such as marigolds and calendulas, to fill in spaces in the bed for the time being. Eventually some of these will probably be replaced with valerian and astragalus (milk vetch), which I’m starting from seed at the moment. A neighbour has offered us some more comfrey, so we will probably end up trying that as a barrier plant also.

Barrier garden

As with our other garden beds, the area for this barrier garden was covered with black polythene for a couple of months to kill back the kikuyu. Before digging holes for the young transplants, I sprinkled the area liberally with lime and dolomite to loosen and sweeten the clay. Then I mulched with wood chips. I made a barrier of corrugated iron against the fence to keep out the pasture plants until the lemon grass and other barrier plants can establish themselves properly.

It will be interesting to see whether this barrier garden works. If it proves successful, we will probably make similar plantings around most of the edge of the house paddock. We anticipate keeping a further strip of weed mat or mulch between the barrier gardens and the vegetable plots.

6 Responses to “Barrier Garden”

  1. Mike says:

    Comfrey and Lemon Grass work reasonably well as a barrier, but only if you have both together — just one or the other is useless. The Comfrey provides a shade zone that the Kikuyu can’t stand, while the Lemon Grass provides the below-ground root blocker. The whole barrier zone needs to be almost a metre wide, though, limiting its use in places where space is at a premium. (Who would have thought space could ever be “at a premium” in a 4 acre holding…? 🙂

    You’re so lucky to be able to grow Olives!

  2. Mike says:

    Not quite sure which area Mike (above) lives but I live just south of you (Kevin). I have seen comfrey work by itself. However, lemon grass just doesn’t fire enough to form a barrier in our climate. We are going to plant a line of comfrey, and a line of canna lillies and hydrangeas. When choosing a barrier remember the golden rule of permaculture: every job done by two or more elements, every element does two or more jobs. In this case, my chosen barriers are prolific biomass producers. Great for mulch and compost.
    We are using a pig to clear the kikuyu. Hopefully it is just a little faster than black plastic. I’ll let you know.

  3. Rebecca says:

    This barrier garden venture is new territory for us, so we really appreciate the comments and suggestions. Thanks!

    I didn’t know that a barrier garden needed to be a metre wide. (Probably should have paid more attention to the permaculture book!) That’s good to know! By some happy accident,the bed I’ve just been working on is actually about a metre wide. I hope that the barrier plants will be useful enough (biomass, stock feed, whatever) that we won’t begrudge the space too much.

    To be honest, I’m not sure how well the lemon grass will do in this spot. When I lived in Kaikohe (just south of here and rather more elevated) lemon grass would only survive the frost if planted in a very sheltered position. This area is generally a bit less frosty than Kaikohe, and our Farmlet is on the midslope of a valley — in a bit of a thermal belt. Still, it does frost here, and it’s entirely possible that the lemon grass won’t survive the winter. We’ll have to wait and see! If the comfrey will work on its own, then perhaps it won’t matter so much. Maybe we’d better hurry up and get the comfrey from our neighbour. I like the idea of using cannas and hydrangeas, too. Perhaps that will be something to try for the next barrier bed we make.

    Good luck with the pig, Mike. We’ll look forward to hearing how it goes on the kikuyu.

    Oh, and yes. . . I think we are very lucky to have olives, as well. They are a favourite treat of mine. I’m watching avidly as the fruit ripen. Can you grow them where you are?

  4. tochigi says:

    Hi Rebecca,

    What the first Mike said is the key:
    “The Comfrey provides a shade zone that the Kikuyu can’t stand”

    Shade is _the_ natural barrier against Kikuyu.
    That is why the hydrangeas would work so well, and I imagine the comfrey too.

    My mother grew up on a dairy farm in Northland (she’s 79) that was overrun by Kikuyu. My uncle used chemicals to fight it (roundup), which eventually killed him.

    My mother’s garden in Auckland was also quite bad for Kikuyu, but a combination of shade, roundup (in the bad old days) and hand weeding has eventually got rid of 95% of it.

    good luck!

  5. Eunice Hayes says:

    I have huge elm trees, the roots of which spread through my yard and make growing anything else in a small kitchen garden very challenging. I have noticed that the fine elm roots cling to comfrey root in a massive ball and stop there, leaving a nice amount of soil around the comfrey free of roots and thus available for tender perrenials. It being April now, I dug up the comfrey and removed the ball of elm roots, then divided the comfrey and planted it in what I hope to be a barrier against the elm roots.

  6. sue cimino says:

    It’s 3 years later…. I would LOVE to hear how well the barrier garden on comfrey and lemon balm did with the kikuyu from your neighbor’s paddock.