Start your seeds 6-12 weeks before consistent warm weather
Lavender seeds need to go through “stratification”, a period of cold before a period of warmth - put moist soil and seeds into a large ziplock plastic bag and put it in the refrigerator for 3 weeks (use a seed starting soil mix) - preferably the vegetable crisper drawer
After the 3 weeks of cold, use a seed tray or large shallow tray - plant 1 seed per cell or 1/2-1" apart - barely cover seeds (they need light to germinate)
Keep the tray in a warm spot or on a heat mat,
water lightly in the morning
Lavender takes a long time to germinate,
between 2 weeks - a month
Keep seeds in an area with lots of light or use a grow light - make sure that the seeds get at least 8 hours a day Transplant lavender seedlings to larger pots once there are several leaves - use a potting mix with a balanced fertilizer You will do a final transplant once the plant is at lest 3 inches tall, it will still have a single stem, and this takes 1-3 months Before the final transplant, begin to harden off the plants by exposing them to partial sun for a few hours each day for about a week
Choose a final location that is sunny, with well-draining soil Make sure the final soil pH is between 6-8,
ideally between 6.5-7.5
Plant the lavender 12-24" apart
For the first year of growth, regular watering is necessary - after the first year, the soil can dry out between waterings, and mature lavender is fairly drought-resistant During the first year, you'll cut back the flowering stems to encourage root development, in year 2, cut back 1/3 of the flowering stems
In colder weather, mulch around the base of the plants, but leave about 6" around the plant to allow air circulation