I have problems with Z-9 rated salvia in 90's temperature. I'm in southern Texas. Is Z-9 or 10 rated agastache better all around on the coast? Thanks.
Hardiest in Z-9b, Cold-Hot Agastache or Salvia?
Certified GKH Gardening Expert
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.