What perennial can I plant with lavender

Go to your local nursery and see what they are selling. Read the cards on each plant and see what their growing requirements are-- water, sun, height, etc. Then select plants whose colors look good next to yours. It's all personal preference.

Moonbeam Coreopsis is a nice yellow bushy perennial.

Most perennials do not bloom the entire growing season. The best you can get is repeat bloom after trimming back flowers. Bloom time is also subjective. If you live in zone 8 your last average frost could occur between 2/22 and 3/30. If you live in zone 5 your last frost could be between 3/30 and 4/30. Look for plants that have colorful foliage to provide interest before and after bloom time.

Lavender needs well draining soil and grows best in zones 5 to 8. It prefers a drier climate and high humidity can lead to diseases. If you have rainy winters place your pot on a south-facing porch, if possible.

I suggest a creeping thyme as it prefers the same conditions as lavender. It blooms in white, pink or lavender from late spring to early summer. Aurinia saxatilis (yellow alyssum) grows to 12 inches tall. Bloom time can be anywhere from late spring to summer. Angelina stonecrop (Sedum rupestre) grows to only 4 inches tall. It's foliage is chartreuse with pink or red tinges during winter. It's flowering stems tend to be leggy, but are good for an indoor vase. All of the above plants are hardy zones 3 to 9.

The ice plant gets its name due to a reflective quality of the flowers and leaves as if they were covered with frost. Unfortunately they are only hardy to zone 8 (10ºF). Ice plant can refer to more than one genus. Ice plants in the Delosperma genus are short (6 inches) and wide spreaders with purple, yellow, pink or white flowers. Whereas, those of the Lampranthus genus are taller and bushier and come in every color except blue. Both genera bloom in summer.

Go see what they are selling at the local nursery since they only stock plants guaranteed to thrive in your region. Ask the sales people for ideas - that's what they are trained to do! You can also scout your neighborhood for ideas and take photos of garden arrangements you like.