Our PTA has both a flat sale as a fundraiser and the Mother's Day plant sale. For the flat sale, the chair shops around at local nurseries, explaining that it's a fundraiser for our PTA (it's usually the same nursery each year that comes through for us). They come to an agreement for a fair price (usually around $6.00/flat I think), then we sell them through an order form for $10.00, which is about $2.00 cheaper than most of the nurseries sell them for. I've wondered why they don't try Lowe's or Home Depot, but it's one of those "way we've always done it" things, and I'm not involved in it, so I keep my .02 to myself. It's the standard fare of impatiens, snapdragons, etcetera.
We also do a Mother's day plant sale the friday before Mother's day and we do make a bit. This is not a full out fundraiser but with a small mark up and the local Agway giving us flats of flowers at cost we make around $700.00 each year. We are a school of 500 kids. The moms really do love this! We do the sale during luch in the back of the cafe. and the kids come up with their money when they finish lunch! It is very simple!
We do a Mother's Day plant sale with various types of annuals in 4" pots we purchase in bulk from a local nursery. This is not done as a fundraiser but rather so that all the kids have a chance to get something for their moms. We also purchase colored foil from a local florist to wrap the base of each pot. The child gets to pick the color of foil.
We do this the same weeek as Teacher Appreciation Week. Each teacher gets a plant as well as one of our gifts that week.
Our school does a spring geranium sale in late April. We just buy a bulk lot of geraniums from a local nursery at a discounted price. We are a school of about 300 kids/1000 parishioners, and we buy 600 geranium plants and sell them after each of our Sunday masses.
We debate every year if we should take orders or just take our chances, but this way makes it less pressure and seems less like "another fundraiser". We make about $800-1000 each year.
In the fall, we buy mums from the same local nursery with about the same profit.
We have found the geraniums to be easier to sell since most people use them as an annual whereas the mums are often planted and return each year.
Good luck with your sale!