Lavender Varieties Companions to Lavender Pruning Lavender
Fertilizing Lavender Harvesting Lavender Where to buy lavender
Lavender will grow with very little care and in very poor conditions.
However, if you want your plants to look great and produce lots of flowers, they thrive with a little help.
I'm going to assume you have provided good conditions for your plants to start with:
Full sun, good drainage. The pH should be on the alkaline side. There are some varieties, like Lavandula lanata, which are very fussy about pH, but most garden lavenders are not. If you really can't grow lavender and you have full sun and drainage covered, then check the pH. If you are going to grow lavender commercially, check the pH.
Hopefully your new plants are going into a spot to which you have added some new soil, so fertilizer is not really needed. You can use a transplant fertilizer which has ingredients to help plants root better.
If you have lavender in a mixed perennial bed, or near roses, it is going to get fertilizer if you are feeding the other plants.
If you have lavender in a border alone, I would start in the spring with general liquid 10-10-10 or 7-7-7. You can also mix in a little granular fertilizer for flowering plants. The granular will be slower releasing and provide nutrients over several months.
After the first flowering, give another liquid feeding with a fertilizer high in the 2nd number; eg. 10-20-10.