Many people seem to be interested in herb spirals, and rightly so if done properly they need little maintenance and can keep you in herbs all year round. For me they encompass all manner of permaculture principles from how close to house you can get it to including a a small pond so frogs can do some of the slug hunting for you.
Basically the idea behind them is to get as many different herbs as possible in a confined area. The spiral and the subsequent hight differences mean that you create a number of different environmental conditions which normally would not be possible in a small space. The small area also means that they are ideal for a small garden and harvesting and watering is easy.
How it works is that you have a spiral bed in which to plant, this is held together with a structure of rock, brick or anything really that can absorb the heat of the sun through the day which in turn heats the soil. The top of the spiral gets more sun and has significanly more drainage than the lower parts, which informs your choice of planting. This means that you are able have thyme gowing almost next to mint or ramsons. The bottom of the spiral often incorporates a small pond allowing frogs and toads to breed and creating a wetter moist environment.
To build your spiral you first need to select a site, about 2m across, this ideally wants to be close to the kitcken but if this means that you have to site it in the shade then you will have to settle for a longer walk. This is at the heart of permaculture principles the siting of your spiral will depend on finding an area which recieves enough sun light to keep mediteranian herbs happy and is not so far away from the house that does not get any use. If you have to pass the veg patch and a green house before you get to it then there will be so many distractions that you will have forgot what you went out there for, or is that just me?
When you have found an ideal compromise between the two measure your circle by estimating the middle and sticking a stick in with a piece of string 1m in length attached to it. This will give you the arc of the circle, use a knife or something which makes a mark to mark this out. There is no reason for it being exactly round but I like it that way, you may just want to do it by eye. Around the outer circle lay a thick layer of cardboard with all the plastic removed, or newspaper, this simply stops weeds growing up through the rocks. Try and face the end of the spiral towards north so as to improve the efficiency, this will make sure that the microclimates you are trying to create are in an ideal situation. However with mine the end does not face north but is slightly in the shade more of the time, like I have said before it will all depend on your site.
Now is the fun part get your rock or what ever you can lay your hands upon, mine is made from rocks and bricks as I did not have enough of either. Start by laying out the shape of the spiral on the ground this will be your foundation. A tip here is to keep the better more attractive rocks for the top, it’s permaculture but it still can be pretty. The rocks around the edge need be only one deep, it’s the middle that you need height. Try and aim for about one meter but again this is not a rule.
As the wall gets higher start to infill with gravel this is for drainage but will also stop a collapse as it gets higher. The type of gravel is up to you use what you have to hand rather than buying something specific. Remember to leave enough space for compost and top soil. You can then treat it as a raised bed. The top of mine has a little more gravel mixed in with the compost to aid drainage. Traditionalists will have you believe that the spiral should go clockwise in the northern hemisphere and anti-clockwise in the south, you can make up your own minds.
Finally the end of the spiral can just be capped with rocks or if you decide for a pond try to make it level with the soil, no lip and have something that creatures can crawl in and out of. Think of it as more of a wet damp area than a conventional pond.
When it’s finished, water it well and allow it to settle. Then you can start to plant it up, the choice of herbs is up to you just bare in mind that the ones which require more drainage go at the top while ones which prefer wetter conditions go at the bottom. One thing to remember is bare in mind the final hight of the herb to be planted as this will effect what can be planted next to it due to the shade it will cast. I would say to leave out things like bay as it grows large and could take over but use common sence. Like with veg growing there is no point filling it with rare and beautiful herbs that you never use, think of what you like and use then find a place for it.
They make an attractive addition to the garden as well as being very productive.
Image taken from CentreforSustainableCommunity.org