vegetative stage begins as soon as the seedling pops through the soil, however if you are talking about vegetative in reference to a feeding chart then typically you feed under the seedling/cutting chart until the plant reaches 4-5 internodes or between 6-10". If you are using an enriched soil you may not have to feed at all for the first 2-4 weeks of vegetation, and I personally don't feed my seedlings anything until they get their first true set of leaves. Hope this helps