Answer: Usually folks ask us how to keep their Jerusalem artichokes from taking over their yards and gardens, rather than how to get them to spread! Seriously, though, your artichokes sound kind of small compared to some I've seen. Are they growing in a shady place? Perhaps the unusual summer weather has affected their growth. Summer's not over yet though -- they may yet reach 6-8' tall.
Harvest the tubers as you need them eat after the foliage has died down (usually after the first frost). They store best right in the soil, but you can also keep them in a plastic bag in a refrigerator crisper for a week or two. If you want them to spread faster than they naturally will, you can relocate some of the harvested tubers to new locations this fall. Don't cut tubers planted in fall -- they're likely to rot. In parting, I offer this gentle warning -- they can become extremely invasive, so locate them away from your other crops and garden spaces. Enjoy!
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