Knockout roses HELP!!!

[jimnks]

Hello all, my wife planted 7 knockout roses in a bed last year, they did fine, this year they have taken off alright, but have new shoots coming out of every plant that are twice as tall as the original plant, the canes are as big around as our tea roses, and the leaves are 3 times as big, but the flowers are the same size as the ones on the original plant. Do you think they froze? What to do, cut back large canes to ground level, cut back canes to level of the rest of plant, or something else? We live about 35 miles west of Kansas City. Have a nice day!!!
jim

[MoPlants]

I suspect that you have two plants growing together, which explains why you're so confused.

I'm not sure if Knockouts are grafted, but most modern roses today are.

The growers choose a rose that's fast growing, highly vigorous and disease resistant. They root thousands of cuttings and plant them in fields. When time comes they dig up the roses, now called rootstock, chop off the tops and graft little pieces of Knockout rose onto the stems. The rose is replanted, the two sections grow together and you have a Knockout ready to sell.

If that rootstock is damaged or if the Knock out is so stressed it dies off, the rootstock begins to grow freely all on its own. Foliage changes, stem size gets huge and the rootstock explodes. Meanwhile what little bit of Knockout is still alive may continue to grow and eventually bloom.

So it's likely all that rank growth you see is rootstock and the flowers are from the remnant of the Knockout. Your best bet is to cut the rootstock stems down to nothing and leave the Knockout parts to grow. However, that rootstock will come back time and again, and rather than fighting it, you may decide to plant a whole new rose plant instead.

[Wahrheit]

Hello all, my wife planted 7 knockout roses in a bed last year, they did fine, this year they have taken off alright, but have new shoots coming out of every plant that are twice as tall as the original plant, the canes are as big around as our tea roses, and the leaves are 3 times as big, but the flowers are the same size as the ones on the original plant. Do you think they froze? What to do, cut back large canes to ground level, cut back canes to level of the rest of plant, or something else? We live about 35 miles west of Kansas City. Have a nice day!!!
jim

The first Knock Out roses that I bought several years ago were grafted on to Dr. Huey rootstock. Interestingly, most Knock Out's that I've seen in recent years were all growing on their own roots.
However, Dr. Huey is pretty much the standard these days (in the USA) as a grafting rootstock.

If the blooms on the big canes are red, it may be very possible that it's Dr. Huey rootstock growing. And if this is in fact the case, those canes need to be removed at the source, which is below the crown.

If left alone, this growth will eventually take over your Knock Out rose, and Dr. Huey is indeed an extremely tough and vigorous grower.