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Since these plants do get quite tall, depending on the variety anywhere from 18 inches to 5 feet, it would certainly be a wise move to place them in the back of the bed. One word of caution--some types do not transplant well and resent disturbance; however, to reduce transplant shock, try cutting back about a third of its growth.The best time to transplant any plant is on a cloudy day or in late afternoon so they have a chance to get settled in before drying effects of the sun set in. Place salvias in the ground at the same depth or slightly below the level they were originally growing.

http://www.armstronggrowers.com/pages/expertise/diseases-pests/armstrong-solutions-syngenta-flowers-salvia will give you guidance. I have grown salvia in both alkaline and acidic soil without problems, however. If it is a hardy variety, it can be planted in the soil (no pot).

The problem may be that you are probably on the upper end of what your agastache can take. Zones are rated on the coolest winter time temperatures and not so much on the warmest end in the summer. On top of that, zones are a guideline, so some areas can have a year or even several years where their winter and summer temperatures are much higher or lower than what the zones suggest they will be.

If you are growing an agastache that is rated for zones 5-9 in zone 9 and you are having a warmer than average summer, the plant will struggle. If this is the case with your plants, then I would recommend looking for an agastache that is suitable for up to 10 to help hedge your bets.

Red salvia only survives in zones 9 or 10 outside year round, so you are not able to plant it in the ground where you live. You can try overwintering it in your house though.

If they are recently planted, it is possible that this one has transplant shock. Just like people, when it comes to shock, some plants (even among the same species) handle it better than others. If you suspect shock, this article may help:
https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm

If they have been there for a few weeks and this suddenly happened, I would look to pests. Check the leaves and roots of the plant closely for signs of pests and treat accordingly.