Knockout Roses Blooming Less Each Year? Try Tomato Fertilizer for a Phosphorus Boost

Two Knockout roses planted three years ago bloomed well the first year, sporadically the second, and barely at all the third. Plants looked healthy with good sun and regular water.

Phosphorus Deficiency

Knockouts should bloom continuously. Declining blooms often indicate insufficient phosphorus relative to nitrogen. A tomato fertilizer (high in phosphorus) applied at the mature plant rate can stimulate flowering.

Winter Damage Check

In cold climates, repeated winter dieback can weaken the plant's blooming capacity. Ensure the variety is fully hardy to your zone and protect the base with mulch.