Chicken grit is excellent for drainage!
Grower's size (yes, what they feed chickens
) is perfect for containers. You can get bags of chicken grit at your local farm store, but I'm not sure about buying in bulk.
I avoid peat-based potting mixes for my semps. Granted, my winters are much warmer, but I have some that have lived in a coir hanging basket for years in a pine bark/perlite mix.
In the ground, they do really well for me when pine bark is mixed with clay soil.
The problem I have with semps in-ground is that zoysia grass that surrounds the bed invades the area and swallows up the semps.
It's a constant struggle to keep the zoysia grass away.
