Dear William,

Thank you for contacting Ask Extension about your Agastache.
These plants do well in average soil but they must have superior drainage. Avoid heavy clay soils that do not drain well. A sandy loam would work well in a garden bed. In containers, use a light potting soil with some sand mixed in for drainage. 

Agastache thrives in full sun and is fairly drought tolerant; however, it may need some extra water if the weather is extremely hot or dry for an extended period. Once the plant is established, too much water or fertilizer will only make for weak stems and possible flopping. In the garden, add a layer of mature compost to the surface of the soil in late autumn (up to an inch). 

Deadheading after the first bloom may encourage additional flowering and also help to prevent self-seeding. Let the stems stand through the winter to provide shelter for insects and protect the crown. Cut them back in early spring and pinch back the new growth for a more compact plant.

Agastache is apparently prone to downy mildew. You can prevent this by improving air circulation around the plant and avoiding overhead watering.

I hope this information is helpful. Write again anytime you have questions. 

Thank you so much Lynne, your info is most valuable and well appreciated, especially as there doesn't appear to be much online about these plants.