Agreed. Sometimes facility improvements is part of the PTO's mission. In our area, the district mows. Period. No mulching, no weeding, no planting shrubs. The school would look like a prison if not for the PTO. Of course, the amount of budget given to this line item is fairly minimal (maybe 2% of the overall annual budget) and we do make all attempts to find business sponsors (landscaping companies) to donate labor and materials where possible.
I don't see any reason why you couldn't do that, unless your bylaws said something specific.
Lots of groups support physical plant improvements. Painting the cafeteria, adding curtains to the auditorium. The landscaping may not soud as impactful or serious, but it falls in the same acceptable category from a "can we?" perspective.
Whether you choose to support this or not is a discussion for your group.
Can a PTO use fundraising dollars on landscaping for the school? Our PTO usually asked for parents or landscaping companies to volunteer their time to help with the upkeep of the school grounds. Our district does not have the funds for that. Historically, we have used fundraising dollars on items and events that would benefit the students. Now, a group of parents is not happy with the way the outside of the school looks and wants to use $1,000 of the PTO's money for the upkeep of the school. Is this legal?