Knockout Roses - What You Need To Know About Them
Knockout Roses seem to have taken the rose growing world by storm as one of the easiest, trouble-free rose plants to grow. Apparently this AARS award winning rose is the most widely sold rose in North America due to its hardiness and versatility.
This rose was hybridised by Willian Radler and introduced to the world in 1999. It’s a floribunda rose that grows to about 4ft tall (1.2m) and as wide, forming a small compact bushy plant.
Flowers are semi-double and loosely formed, cherry-red fading to pink as it ages. Many clusters of flowers are borne on the plant which have very little fragrance. If they’re not regularly dead-headed they will set hips in shades of orange.
Knockout Roses are a very versatile. They can be planted in rows as a border or hedge, where they look terrific en masse. They are also compact enough to be grown in containers on patios and decks where their non-stop blooming can be shown off to advantage. You can also buy them in tree form as a standard rose.
They are supposedly shade tolerant, resistant to black spot, mildew and rust. Though a lot of this depends on them being planted correctly and having their cultural requirements met - there are cases where this rose does get disease problems but it is less prevalent to disease than some of its fussier counterparts.
Knockout Roses are said to be “self-cleaning” meaning they don’t need deadheading, but to promote continuous flowering I would recommend lightly deadheading this rose bush during the growing season, with the emphasis on “lightly” as the flowers bloom on new wood. If you don’t deadhead, the rosehips use up a lot of the rose’s energy (forming new seeds within the hips) instead of the plant’s energy being used to form flowers.
They are supposed to be hardy down to USDA zone 5, however the occassional loss does occurr in this zone over the winter so I’d be inclined to cover them during that season to prevent any losses occurring with your knockout roses.
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We had professional landscaping done at our home last year. Four knockout roses were planted as part of this landscaping. We have tried repeatedly to contact our landscaper, without any results. The rose leaves are covered with small holes and most of the leaves are dying. These are not aphids, as I know what they look like and we have no evidence on the leaves. The blooms are not affected, but are becoming very sparse. Any suggestion as to what may be causing this and is there any treatment?
@Christine
It’s hard to diagnose the problem without a picture of it but it could be some kind of leaf spot fungus that is causing the leaves to get small holes in them so you might want to try using a general fungicide on both the tops and underside of the leaves. Is there any discoloration around the small holes? Anthracnose can cause leaves to get a shot-hole appearance to them but this fungal disease starts with small purple/black circular spots appearing before the centre of the spots dry and fall out, and you haven’t mentioned if the holes have a purple edge to them. The leaves also tend to go yellow so are any of the leaves yellowing? Are the leaves skeletonized (rose chafers or Japanese beetle) or are they definite holes? The leaf cutting beetle chews neat circular pieces from the edges of the leaf but not in the middle. It sounds more like a fungus to me than an insect causing the damage, so I would try spraying with a fungicide. Ask at your local nursery for a reputable one and always follow the safety and usage directions on the pack
When do I prune my KNOCK OUT ROSES?
@Betty
It depends where you live. In Australia - in warm climates like Sydney - prune in mid winter. In the colder climates of Australia, prune after the last frosts.
In warm US climates like Florida and Arizona prune in late fall or early winter. In moderate US climates early spring is the best time to prune, and in the colder northern climates of the US where roses have to be covered over winter, it’s best to prune them after the hard freezes are over or when the Forsythia starts to bloom.
The above give a general idea, but to be absolutely sure of the best time to prune in your particular area, I’d visit or phone your local plant nursery and ask the horticulturalist there; that way you’ll know you’re pruning them at the perfect time for your area and can get them off to a good start.