I've had an indoor ficus for many years. It's proved hardy. But I recently left it in a south window accidentally for 2 weeks while I was traveling. It got very dry and dropped at least half of its leaves. I'd read that a rescue therapy was to water it well, cover it loosely with a plastic bag, and put it in a cool place (the basement). I did this for about 2 weeks, and now have had it on a shady porch for about a month. There has been no further leaf drop, but no new growth either. How can I encourage new leaf growth?