Answer: You are almost asking for a miracle, but there is "possible hope". You are right, that is a very tiny space between the pavers. Unfortuantely, although the idea of seeds sounds good at first, the weeds will probably continue to get a jump on the desired seeded plants. Hand weeding will be a big job because that is such a long expanse of pavers, so you might still wish to consider some judicious use of least-harmful herbicides at least in the beginning.
There are some possible plants, although your selection will depend on whether the path is in sun or shade and in a sheltered position or not. Thymus praecox (creeping thyme), Lysimachia nummularia (creeping Jenny), Sagina subulata (Irish moss), and Waldsteinia fragarioides (barren strawberries) are all possibilities, as are some of the very dwarf sedums which can be started by "sprigs".
Unfortunately, all of these would do better if set out as very young plants (nearly seedling size or as barely rooted cuttings), probably in early to mid-spring, so you will still have the weed battle this season. You might hand pull or resort to some glyphosate periodically this summer and fall to keep the current crop of weeds from going to seed and compounding your problem next year.
To purchase these plants, you might wish to contact a local nursery and see if they will order or grow some in very small sizes for you next spring; another possibility is mail order although the plants will be larger. (This might work best if you can plant them along the outer perimeter of the walk and encourage them to "run" inward towards the center.)
You should also find these at Bluestone Perennials, 7211 Middle Ridge Rd., Madison Ohio 44057 (800-852-5243); Carroll Gardens, 444 East Main Street, Westminster MD 21157 (800-638-6334); White Flower Farm, PO Box 50, Litchfield CT 06759 (800-503-9624) or Wayside Gardens, 1 Garden Lane, Hodges SC 29695 (800-845-1124).
As an alternative, creeping thyme or Thymus serphyllum might be a possibility from seed. Seed is available from Burpee and you may order a catalog at the website http://burpee.com/ or call 1-800-888-1447 Mon.- Fri. 9 am - 8 pm ET, Sat. & Sun. 9 am - 5 pm ET.
Good luck with your pavers!
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