Q.how long can I store black lily bulbs
My mum is now in a nursing home and wants to plant black lilies in their garden. If I dug them up, how long can I store them for, as I can only give her a few at a time. Also, what is the best thing to store them in?

Although "black lily" can refer to either a calla or an Asiatic lily, the procedure for moving them is about the same. I don't think you really need to worry about storing; just dig up the plants that you want to move as close as possible to the time you'll be traveling. Use the tips for transplanting here: https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm
and here: https://www.gardeningknowhow.com/ornamental/bulbs/calla-lily/transplanting-calla-lilies.htm
You can carry them in anything that's convenient and large enough to fit the clump you've dug Thinking in terms of transplanting instead of lifting and storing allows you to move the plants and just about any time -- even when they are flowering!