In the heat of summer is not the best time to plant anything especially something in full bloom. The roots of your plants have to settle in before the plant will thrive. Your plants are trying to settle in and support the plant and flowers. What they need is shade for a while so they are not stressed by trying to cope with hot weather and grow too. Is there some way you can shade them and still give them indirect light. Perhaps put them under a patio table for a couple of weeks or under a roof eaves. Look for a shady spot especially in the heat of the day

I think the above post is correct about your current situation. Your lavender is probably suffering from transplant shock.

Long-term though, you also should consider that lavender needs very well-drained soil -- so something gritty or sandy mixed with something organic (like compost or humus) is best. Lavender also needs neutral to mildly alkaline soil, so you may need to add a small amount of lime to make it happy. Avoid mulch as it can trap moisture at the base of the plant, causing rot. Good luck!

Ditto the info above--an established lavender in full sun + excellent drainage is ideal but not one that's trying to send out root growth while coping with all-day mid-summer sun & high temperatures. My healthiest lavender is a second-year winter sown plant (from seed) growing in a container that gets just a few hours of late afternoon sun + whatever moisture is provided by Mother Nature.

I normally plant out from May through early June then wait until September to resume in order to allow plants the optimal conditions for establishing a root system that will sustain them.

when water is coming out the bottom.. that should be a fair indication.. that you are overwatering ... too often ...

these types of transplanting are better done in spring .. rather than august ... for a multitude of reasons ...

all transplanted stock.. should be protected from full sun to give the roots time to get pumping some water .. say for a week or two.. ... and again.. spring sun is much less intense than august sun ...

and you might want to put those pots on something to get them literally off the deck [a trivet??] .. as water can rot things ... so you lift a giant water holding pot.. off the decking a bit ... so that the decking itself.. can dry

so.. late transplant.. in the wrong season.. with to much sun.. and too much water .... in a questionable media ...

september.. as the sun wanes.. with cooler nights.. might have been a better transplant season ..

and finally.. i dont know how good the stock was to start with ... you obviously got stock nearly past full bloom.. no matter what you do.. it was in decline.. as far as this years flowers went.. so the goal is to find out if you can get it to live for next year ..

i never had a lot of luck with lavender.. in MI .. they died every spring.. and i THINK it had to do with too much water.. root rots ... perhaps.. lavender.. is not the best thing for pots.. i will defer to others on that ...

insert finger to 3 to 4 inches.. and do not water again.. until the soil feels like it is drying .... on some level.. i think you are trying to kill it.. with TOO MUCH LOVE ...

ken

ps: did you thoroughly moisten all of the media.. PRIOR to planting .... because if you didnt.. you may have intermittent areas of too dry.. and too wet ...

Here is a link that might be useful: flip to the IMAGES

The OP is in WA state and it is seldom ever too hot to plant here, even in midsummer :-) The PNW has very different growing conditions than the rest of the US, so what may be appropriate in Ken's MI (and with the other responders) has little bearing here.

The lavenders are suffering from over-watering. Even newly planted lavanders do not need daily watering here. Ken's point about the potting mix may be applicable as well. Above all, lavender needs excellent drainage and many potting mixes are just too moisture retentive. That, combined with daily watering, may be over the top.

Allow the soil to dry out between waterings. And you might want to research a better potting medium - something very barky and gritty with very fast drainage. A cactus mix or Al's gritty mix would be great.

You may also wish to consider that lavender are most comfortable when slightly root-bound. Planting them in such a large container increases water retention around the roots. I would start them in a much smaller container (only a couple inches larger than the root ball), then gradually move them up to those pictured as the plant grows. It does not necessarily indicate overwatering if water runs out of the bottom -- in fact, it should do so pretty quickly if the soil is well-drained.

As you may have gathered, lavender are somewhat fussy plants. However, the PNW climate (as I understand it, though I know there is a lot of variation from the west to east) has some Mediterranean characteristics (namely, relatively dry summers) so you may have more luck than us poor souls who deal with ridiculous humidity on the east coast.

If I have to transplant anything in mid summer I cut down all flowers. Right now the plant is putting energy into bloom & seed instead of establishing roots.

& yes, you are watering it too much.

If anyone thinks lavenders are fussy then you've never grown Munsteads. They are pretty much bulletproof.