Hello! My begonias are splitting open and falling over! Two are severely damaged, I need to know if I can prevent the same thing from happening to the others and what to do to the ones that have already suffered damage.

I have 9 tuberous begonias that I bought last year when my wife and I bought our house, this is only my second year really keeping a garden. I live in the Seattle area, and we've had a very wet, overcast spring (even for this area). Last year, they took forever to grow, but by August they were healthy and displayed nonstop color until autumn. I had unknowingly planted them in full sun (6-8 hours a day), and even in a two week stretch of triple digits last year, they thrived. I over-wintered the tubers in the garage, started them indoors in February, and brought them outside in May. I planted them in a different spot this year, one that gets MUCH less sun. They grew twice as tall as they did last year!

Yesterday, the tallest and thickest of them had fallen over, and part of the stalk had split open into sort of a mushy stringy area, and a similar spot opened up higher up on the plant. I cut off the wilting stalk (about a foot and a half's worth of the plant).

Today, the same thing happened to another one. What's going on!? We finally had summer hit with high temperature ... can I do something to protect these guys? They're so beautiful and they're in the front of the house, I'd hate to lose them!