Purple Robe Locust Root Sprout: White Flowers Mean Rootstock, Not Cultivar

A homeowner replanted a root sprout from a borer-killed 'Purple Robe' locust (Robinia pseudoacacia 'Purple Robe'). It bloomed white instead of purple. They ask if they should replace it.

Grafting Explains the Color Change

'Purple Robe' is grafted onto black locust rootstock. Root sprouts arise from the rootstock (white-flowering), not the purple-flowering scion. The sprout is genetically the rootstock—white flowers are normal.

Options

• Keep it: Fast-growing, tough, white flowers, same borer susceptibility
• Replace: Buy a new grafted 'Purple Robe' from a nursery for purple flowers
• Graft yourself: Advanced—bud-graft 'Purple Robe' scion onto the sprout

Borer Warning

Locust borers (Megacyllene robiniae) attack all black locust varieties. The rootstock sprout has no resistance. Monitor and treat proactively.