Yes, in general the first pruning of tender plants such as lavender and sage should be done after the danger of frost has passed so that means the first week of May in Western Washington. The logic is that pruning always stimulates growth and new growth is more susceptible to frost damage so pruning late prevents frost tipped growth. Of course you can break this rule and get away with it if the spring weather is mild or if you don't mind risking a little brown tips or frost damage on your lavender. Try to remove no more than one third off the tops of the lavender plants and do not cut into the thick woody trunks. One more thing - lavender plants are not really long lived so after 5 yo 7 years you may want to replace old plants with fresh young plants to keep your lavender looking and smelling it's best. Keep growing, Marianne Binetti