I have tried to grow lavender numerous times over the years with poor results.
The problem is that I top-dress with compost every couple of years to create rich soil and I water when necessary with a sprinkler. Most of my butterfly plants thrive under these conditions, but not lavender.
Veronica and perennial salvia are great substitutes that will have two bloom periods if you cut them back in July.
If you still want to try and grow lavender, here are some notes from the Mo. Extension Service.
- Control the amount of water going to the plants. Keep it on the dry side.
- Use raised beds ….at least 12 inches.
- Try different cultivars.
- Plan on losses – 20% to 25%
- Plants do well in hot and dry weather.
- They use weed cloth to reduce weeding.
- They also have training available during the year.
- There is a good section in the video below on propagation.
Butterfly Gardening 