Fresh leaves up to 3 weeks in the frig. Keep them dry and in zip lock bag. I'm talking common milkweed. You can freeze common milkweed leaves Dr. Urquhart said. Just stack them up, take out only what you need for the day and keep the rest frozen. Have you considered planting tropical? You can start some seeds in probably mid July and it will be ready by the time school starts.http://www.johnnyseeds.com/catalog/sear ... =asclepias
Order the Silky formula mix. This gives them more protection, too since it is more toxic than common milkweed. I've been planting mine in those large totes or round plastic barrels. I think someone said you might be able to get them as the dollar store. Drill holes in the bottom for drainage. I put in some pine bark mulch to take up room, Sta-Green potting soil with soil moist and fertilizer, then plant the seeds. Keep them watered.
I just raised 168 Monarchs. I'm going to have a big release this Sunday if it doesn't rain at 3 PM at Meadowlark Botanical Gardens in Vienna, VA.