Lavender

[Laurence]

In which period of the year shall I trim my lavender bush ?

[WendyW]

You need to prune the bush once the flowers have died off. If you want info on the best way to prune it that take a look at http://www.abc.net.au/gardening/stories/s339149.ht
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[Cetti]

For all Lavender, the Old English or French varieties trim back in April, taking care not to prune into the old wood. This is according to "The Flowering Shrub Expert" by Dr. D.G. Hessayon.