Answer: Japanese wisteria, Wisteria florabunda, would bloom earlier than the Chinese wisteria, Wisteria sinensis. This might explain why yours is later than many of the plants you see. It is also possible that yours is in a colder microclimate than other vines in the area. If yours was grown from seed, there might also be a slight genetic variation that causes it to be slightly more cold sensitive and delay coming into growth. As long as it seems healthy otherwise, I am not sure there is much you could do about it.
With regard to fertilizing, as long as your soil has at least average fertility, additional fertilizer is not strictly necessary as a supplement. You might use a complete granular fertilizer such as 10-10-10 in early spring according to the label instructions, and/or a top dressing of compost. In some cases where gardeners have overfertilized a plant it can cause excess foliage growth at the expense of flowers; this is one of the causes we would look into if an older vine has never bloomed yet because sometimes a gardener will be overzealous or overly helpful in trying to encourage bloom and inadvertently contribute to the lack of bloom by overfeeding the plant. If you stay within reason with the fertilizer and your soil is not overly rich then there should be no problem.
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