How to grow & care for a lavender hedge
1. What variety of lavender should you choose for your hedge?
That's right there is more than one type of lavender you can use for creating a hedge. The basic two types are English and French however there are now several new types in nurseries with more showy flowers. Most of the new types I have seen tend to be more closely related to French lavender and should be cared for the same way. For more information on the differences between French and English lavender click here to see another blog entry I've written on the subject.
2. Choosing a location for the hedge.
Lavender is not an incredibly fussy plant but It does like sun and I wouldn't grow it in a very shady spot so don't plant it against a south facing wall (or a north facing wall if you are in the northern hemisphere). The other good things about lavender is that it is fairly drought tolerant so irrigation may not be required depending on your local environment. As an example I only really water my lavender at home in the very hottest part of summer and it is growing just fine.
3. Soil preparation.
Even though lavender is not a fussy plant you might as well do some soil improvement before you plant unless your soil is already in fantastic shape. My reasoning behind this is that hedges are usually planted with the view that they will be there for a long time so if you don't improve the soil before planting you wont have the chance to do so in the near future. Lavender being of Mediterranean origin prefers slightly alkaline and free draining soil so mushroom compost is an ideal candidate for soil improvement. Dig some through the area and its sweetness will ensue more alkalinity and because it is compost it will improve soil structure and therefore increase drainage in clay soils (or conversely increase water holding capacity in sandy soils).
4. Spacing the plants.
Spacing is important when planting a hedge. The main point is that you don't want to space the plants too far apart as they may not grow wide enough to mesh together which is what hedging is all about. Planting them too close is not so much of an issue as it just means they will mesh together faster (but will be more expensive as you are using more plants). The plant tags that come with the seedlings you buy will specify the spread and height of the plant when full grown and you can use that information to figure out what spacing is required. Different lavenders have different widths so using the plant tag information is ideal but if you want a precise figure I suppose if you planted lavender with a spacing of about 40cm it would mesh together nicely.
A row of Avonview lavender that I planted for a client. I used 40cm spacing which should provide a fast meshing of the plants.
5. Planting out the seedlings.
Some basic rules I like to follow when planting out seedling are timing and watering in. In terms of timing I mean planting the lavender in early spring which gives it a good chance to put on some healthy early growth. Also as with planting out any small seedling, don't plant it out in extreme weather (either extremely hot or freezing frosty weather). Watering the hole you dig to plant the seedling and then the seedling in situ also ensures a happy seedling.
6. Feeding the seedlings.
Adding some pelletized chicken manure after planting is a good idea to ensure adequate plant nutrition. Once established I would feed the plants every year when the weather starts to warm up and again a couple of months later.
7. Tip pruning the plants.
People have different ideas about when to first prune lavender plants. I like to let the little seedlings establish for some time before I give them their first pruning. I wait until I notice that the plants have put on some growth (say 25% of their starting size) then prune them back by about 10%. The first pruning I tip prune the entire plant to encourage more branches to develop all over the plant. After that I wait until the plants have put on more growth then after that I tip prune the top of the plant which has the effect of making the sides kick out. Keep doing this until the sides mesh together and form a rough hedge. After that I wait for more growth then I prune the hedge to a desired shape.
8. Shaping and maintaining the hedge.
Keeping your hedge trimmed to a desired shape is easily achieved if you keep on top of things but you may get to a stage where the hedge has vastly outgrown its desired form. From there you will need to cut back the hedge back to the desired shape. If you have let the grow too much the hedge may look very woody after this heavy pruning. If you have English lavender do not prune back to the point where you see no leaves and only woody stems as it probably will not grow back. French lavender and most of the new style French variants can be pruned back quite far and still come back. The rule I follow is that I cut back as far as I can so long as I see at least some leaves (often tiny) and no further. So far I haven't killed a lavender hedge by following this principle.
French lavender hedging I maintain in desperate need of trimming. You can see the shape is starting to degrade so the next time I prune this hedge I'll cut it back quite hard.