I'm in south central NH, zone 4 (mostly it's 5 around here, but we're in a cold spot). My 2 mature hardy kiwi vines, 1 male and 1 female, grow in pure sand with maybe 4-5 hours of full sun, on a VERY sturdy
trellis. I prune them back very hard after fruiting, which entails my taking off dozens of long, reaching vine branches. Probably a couple hundred feet of vine. They barely fruited for me until I got serious about mulching, then both fruit and overall growth took off. I LOVE them, but have to say, their growth pattern and vigor is very similar to bittersweet.The last of their fruit is typically ripening after several frosts, with all the leaves gone. If there's an early HARD frost, the unripened crop is lost. They reach sublime flavors best when ripened on the vine, but if ripening has begun, they'll ripen acceptably indoors if you have to pick to avoid a freeze.
Although not a lot of fruit here hits the ground,
enough has that if it was going to grow from seed, I think I would know it. No sign of that, and no sign of it spreading by
roots, either. A couple long vines that hit the ground did set roots, but the vines are pretty serious about going up, not down. A few years ago I planted more, in good garden soil, with much more sun. They are just coming into production, and are very vigorous and happy where they are. No sign of them spreading beyond where they were planted, though. This is not a plant to ignore; it needs tending. Don't put it near trees you care about and walk away; death by strangling seems pretty likely. That being said, I would far rather have a vigorous plant that needs restraint than a fussy plant that needs pampering.
They are tricky to harvest (at least mine are) because the color change when ripe is so slight that you really have to go by feel. By the time one is picked I may have lightly squeezed it a dozen times or more. That's easy, contemplative time when picking for myself and friends, but would be expensive time if picking for sale. What seems to happen is that growers pick them when they've attained full size,
sell or share them, and those who try them end up with sour, hard fruit. At their best, they are softer than a ripe banana, with flavors that develop in your mouth and make your eyes roll back in your head. I've grown some outstanding pawpaws here, ripening in the same season, and when given both most people prefer the kiwis. That's how good they can be. But, the difficulty of picking them when perfectly ripe completely accounts for their being relatively unknown.
I don't weigh them, (eating them too fast) but do keep count as I go. Last year my one mature female vine produced over 2100 perfect fruit. A friend who has similar soil has been growing the arctic kiwi for years now. No one could say that it's vigorous, let alone invasive. In a good year she gets 2-3 dozen small fruit.
To my mind hardy kiwis are a lot like comfrey. If you mismanage or ignore it, you'll have a big problem on your hands. I don't think that building a strong trellis or yearly pruning is a lot to ask of your average
permie, but an unattended kiwi vine would be a disaster for a hands-off homeowner.
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