So far, the patio question is the only "landscaping" tagged question to come up. Only one other "landscape" question was asked (about lawns). To me it seems like we could attract more landscapers to this site, and the site would be better for it. But so far at least, we haven't.
The small overlap with DIY doesn't bother me in the least. When I looked at the DIY site just now, I quickly found a few questions about stump removal or lawn care, questions which they consider on-topic, but would clearly also be on topic here. Perhaps in the future they'll transfer those questions here?
I don't think of myself as a "DIYer". I have no interest in Home Improvement. And (for better or worse) I see patio construction as a completely separate topic from "Home Improvement". I think that this site is more likely to attract professional landscapers than the DIY site is, because their jobs tend to have more overlap with gardeners than with home renovators.
But if the landscaping off-topic is too much of a hassle for attracting good gardening discussion, and we haven't attracted any landscapers here by the time we're ready to leave beta, then I'd strongly prefer we remove it from the title. Otherwise, we'll be constantly confusing newbies by moving their seemingly legitimate landscaping questions to the home improvement site.