Are dahlias annuals or perennials? Annual dahlias can become perennials; it depends on how successful their over-wintering is.
I purchased a dozen annual dahlia plug-plants early in the summer. They were a mix called ‘harlequin’. Once they flowered in late summer (they seemed to be held back by the unusually prolonged, very hot weather), they produced flowers with a mix of colors: including pale orange, plain yellow and pale lilac. My favorite was this lovely red and yellow one:
With winter care I want this dahlia to become a perennial. There are different ways of doing this but I’m going to be leaving them in the ground, well covered.
Once the dying stems, affected by the frost, have been cut down, I’ll be covering the soil, which holds the fleshy dahlia tuber underneath, with a piece of slate. On top of that I’ll place a pot of spring bulbs. This should ensure that the tubers don’t dry out (which would cause them to shrivel and die), and also protect them should there be any severe winter frosts.