Tuberous Begonia Emergency!

Auburn, WA

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.

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!

Thumbnail by thaniel
Long Beach, CA(Zone 10a)

I'm hardly an expert on TB's, but from what you described, it sounds like they are getting too much water, which is causing them to collapse.
I've always planted them in solid oak leaf mold, not potting soil. Potting soil seems to be too wet for them and they do what you described. The oak leaf mold holds just enough water and drains well for them and keeps the tubers from rotting.

If your TB's are the UPRIGHT variety, you may need to stake them or build some sort of "cage" around them to keep them from toppling, as they tend to get top heavy.

The cascading varieties won't need any sort of staking, obviously, but may need to be cut back a bit when they start getting "leggy".

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