I have 'Frost Proof', it is a cold hardy gardenia to Zone 7. It overwintered completely evergreen and is currently blooming. 'Double Mint' is just another cold hardy cultivar. Not sure if it is more cold hardy than 'Frost Proof'. (The marketing says it is 'improved', but how? (or is it just marketing?!)

Perhaps with good location in Zone 6 and some protection, okay in a normal Winter. Terrific line of plants though, I was amazed given their temperamental status as indoor plants!

I think it might be too late to plant this in the ground. They really need to go in in early Spring so they have time to get established.

If you have a bright, but cold sunroom, (average high temp in low 60s, and maybe 10 degrees cooler at night) that would be ideal for overwintering at this point. Then plant out in May of next year.

Or plant out now, but water, mulch and protect with a tent over winter.

I think if you got it into the ground after the heat dissipates, the fall will help get it established, though I would protect it this winter as recommended above. Just don't put it in the ground right now in the dog days of summer.

'Chuck Hayes' is one of 'Double Mint's' parents, so it is a tough plant. My 'Chuck' has been very resilient, though 'Double Mint' purportedly does not turn dull green in winter like 'Chuck" does.

p.s. the patent states that 'Double Mint' is only hardy to Zone 7. Never trust a Home Depot tag! But I would still give it a go outside. Gardenias often have a ton of issues indoors if not given optimal conditions and even then, it is hard to keep the pests away from them.

Here is a link that might be useful: Double Mint

This post was edited by mistascott on Sun, Jul 21, 13 at 18:03

Here's a thread from the New England forum about growing Gardenias.

Here is a link that might be useful: New England gardenia thread