I usually put pots out when the trees grow enough leaves to make shade to put them in. I settled on that as an intuitive rule. But we had some very warm days last week (for early March, 70s) with mild nights at least ten days out, and cloudy/rainy weather. I decided to put a couple things out - two Brug cuttings, pot of tropical milkweed cuttings, Aloe, Agave, Sanseveria. They are against the house for a little insurance. Oh and Epiphyllum hung under a limbed up Magnolia.