How does NYBG plant so many different plant species together without them cross-pollinating?
Great question! In short, only plants that are closely related to one another are able to cross with each other easily. For example, plants in the species Brassica oleracea are often selected and hybridized, giving us food crops such as kale, brussel sprouts, and cabbage. These are many different types of food, but all come from one species!
In short, unless plants are very closely related, cross-pollination is not generally a concern. Additionally, if plants do cross-pollinate, that means that their babies--their seeds--will be hybrids. The parent plants will not change in appearance at all, and will not become hybrids.
I hope this helps! Please feel free to ask if you have any further questions.