I've grown hibiscus from seed and Usually for the first year they do well in 1 gallon pots. But you are in the next lower zone, so you may want to use a 2 gallon to give them room to grow. They grow well in pots. I'm sure that adding compost to the mix would be fine. Manure too, if it is well rotted.

Thank you for that information. I potted them all in 2-gal containers. I planted another dozen or so in an out of the way place in the garden. I'll hope to dig them next spring, pot them up and give them to a plant sale. I hope those in the ground live over and be ready to grow.

I planted for my garden club plant sale in April, but hibiscus don't leaf out until May. I couldn't take them to the sale because they looked dead. I had potted up a dozen, and I lost 4 over the winter.

I wonder if I dig them early in the spring, pot them up and put them in a greenhouse if they'll leaf out some before our June plant sale. Or perhaps I should pot thm up in the fall and let them overwinter in the greenhouse and hope they leaf out by June. I just discovered that one I thought was dead is just starting to grow now...June 12.