Lavender is one of the oldest and most widely used herbs in history. The Greeks used it as a laxative and the Romans used it as stomach remedy. We grow it today for its wonderful fragrance. We use it in sachets and dry it to bring a bit of summer to the cold winter. This native of Mesopotamia, however, is a bit tricky to grow in cooler climates and propagating this legendary tender perennial can have mixed results. One way to make new plants from old is to divide your old plants when they've grown out and left a dead centre.
Find a plant that has grown out and thinned out in the centre. As plants age, the centre thins out and dies back, just like the inside of an evergreen tree drops its needles as the ends of the branches add new growth each spring. In order to keep the centre vital, plants should be pruned back each year but eventually, they grow out too far and the centre looses vitality.
Check to see if any outer branches have set down roots. These are called "runners" and can be chopped off between the plant and the new roots, dug up and planted in a sheltered "nursery". They will be sturdy plants within a few years.
Pull the bushy growth back to see where the main plant has grown out. These rooted bunches of branches will be your new plants. There should be several bunches.
Dig as many holes as you have bunches to plant. Your lavender's new homes should be about a foot deep in an area where the soil drains easily and your it will get plenty of sun. Line the holes with some good compost-enriched soil and scatter a little garden lime in the hole to give your new plants a quick shot of calcium.
Dig around each bunch with your garden spade. Plunge the shovel straight down, since lavender roots are quite deep.
Once you've dug around each bunch, separate it from the old plant by driving your spade straight down between the old plant and the centre of the new plant and lift gently with a garden fork. Be sure to get as many of the roots as possible. Trim off any sections of the old plant with a sharp knife. Discard the old centre.
Make a cone of soil in the new hole and set your lavender plant in the hole. Move each plant as soon as you dig it up. Set each plant at the same height as the old plant and fill in the hole around it. Water gently but thoroughly and adjust plant height, adding more soil if necessary.
Shade your new plants for a few days until they recover. Avoid watering too much--lavender does not like to stand in water.
Divide your lavender in late summer or early fall. You'll have enough time to see if your new plants have taken hold.
Don't over fertilise or use nitrogen-heavy fertiliser with lavender.