They will need water at least the first year until they are established. Then some need little, moderate or regular water. In hot weather Betsy says - plants - Guaraniticas, should be watered every 7 - 10 days. These are guidelines. I usually water my lavender deep once a week. Course that depends on the soil they are planted in too. If you do a little home work you can be successful and be rewarded. I would think "blk & blue" would be an annual for you so you would have to water. I think of hauling a watering can around as weight - bearing exercise :)

Salvia and Lavandula are both Mediterranean plants, meaning they like wet winters and dry summers. They are definitely compatible. As Phoebe said, you will need to water both plants regularly until they develop good root systems. After that, they are drought tolerant. That doesn't mean no water, but you can get away with water much less water than other plants.

Have you grown Lavender previously or seen it grow in your area? In zone 5, your selection will be limited.

Here is an example of Lavender and Salvia growing side by side in my yard. Unfortunately the Lavender was not blooming when this picture was taken.
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Hi Vicki - gorgeous - I see you must have great conditions for these 2. That salvia is quite large isn't it? I'd like some large ones like that too.

I planted Lavender Vera and Munstead last year in another area that has great drainage and they are wonderful. Typically our heavy clay doesn't do lavender justice. I've found I have to condition the soil quite a bit and raise the beds to grow salvia. I get small plants from Bluestone and am going in a couple weeks to buy a half flat of liner sized lavenders - that will be 36, and another half flat of salvias. They have a good selection for zone 5 so now the task will be to sort through the descriptions. I've grown Salvia May Night at my previous home in a raised bed and it did fine but it never achieved the size I've seen in photos. By now it should be gargantuan but I'm not there to see it.

Thanks again for the photo!