Knockout Rose Cutting Blooming Pink Instead of Red: Reversion or pH?

Three Possible Reasons

A cutting from a red 'Knockout' bloomed red last year, pink this year. The mother plant still blooms red.

• Fertilizer change altering pH/nutrients.
• Soil pH too high (alkaline)—add coffee grounds to acidify.
• Cutting taken from rootstock, not scion. Always take cuttings from the highest, most vigorous growth on the grafted variety.

Verify the cutting origin. If from rootstock, it will never match the named variety.