The best time to plant knockout roses is in the spring or fall. Make sure there is no threat of frost or they may not last through it.
Plant Knock Outs in spring or fall.
They'll have less risk of transplant shock when the temps are mild.
In-ground: Add 2-3" of mulch, leaves, or pine/fir boughs around the base of the plant. A heavy snow cover will also help insulate and protect the plant through the winter. Also, the winter winds can really dry out the plant so you may want to wrap the plant with burlap.
Can I cut my rose bush to the ground? Yes, but it's not usually necessary. The only reason for cutting rose bushes to the ground is if all of the canes are either severely damaged or dead. It's better to follow the steps above to give them a heavy pruning, rather than just cutting them down to the ground.
After several days of below freezing temperatures, create a mound of soil, compost, shredded leaves or evergreens 8 to 10 inches deep over the base of the plant. Mounding keeps the rose uniformly cold, which reduces the chance of damage caused by cycles of freeze and thaw.
The first pruning is done in late January. At that time, Knock Out roses are cut back by about one-half their height or more, but no shorter than 2 feet from the ground. This prepares the bushes for the outstanding spring/early summer bloom period. The bushes are cut back again at the end of August or early September.
Apply a granular slow-release fertilizer such as Miracle Grow to the newly planted rose bush. A healthy application will help it recuperate from its replanting and adjust to its new location. For lush growth, continue a monthly application until cooler weather in the fall.
Mound soil 10 to 12 inches around the base of the plant to insulate the crown. Surround the plant with a wire hoop to form a collar. Fill the collar with leaves to insulate the canes. For extra protection, wrap a piece of burlap around the collar and secure it with twine.
'Knock Out' roses are cold-hardy and heat tolerant. These flowers can withstand temperatures down to 10°F and periods of frost before going dormant. In colder climates, help insulate the plant's roots by adding a layer of organic mulch, such as straw, near the base.
Knock Out Roses can also be planted safely between September and the beginning of November. The roots will have enough time to establish themselves, although they won't be as hardy as spring-planted roots.
Deadheading. “Removing spent blooms will allow your Knockout Roses to focus their energy on producing new blooms more quickly. We recommend removing faded blooms as soon as you see them or every week. — John W., Prairie Gardens Plant Expert – Find him in our greenhouses!
When to Plant in the Fall. Don't stick your plants in the ground mere days before the first expected frost. Your roses won't have time to get settled in and become established before the harsh winter weather hits. The right time to plant is about six weeks before the first predicted frost date in the fall.
Where to plant: As long as there is enough sunlight, Knock Out roses can be planted just about anywhere in your garden. They will do exceptionally well when planted in south and east-facing areas where they will receive the most sunlight. They will tolerate part shade well; however, flowering may be reduced.
Fast Growing: Within a month or two you'll think these roses have always been there, and they're quick to respond to pruning.
We've found that pruning just above an outward-facing bud will promote a wider, bushier rose bush. Knock Out Roses can be pruned lightly throughout the active growth season. Deadheading spent blooms or clusters will encourage quicker formation of new buds and rebloom.
I personally suggest you to apply Fertilome Rose Food, Espoma Rose Food, or Mills Magic Rose Fertilizer.
Your sign to winterize your knockout roses comes in the form of the first hard frost. Once that first frost melts, it's time to start trimming. Completely remove any dead vegetation from your garden and cut the live roses back by about ⅓. Now your roses are ready for winter!
To maintain a size of 3–4' w x 3–4' h, Knock Out® Roses should be cut back once a year to 12” high. Check your rose bush from time to time in late winter/early spring, and when you start to see new shoots growing from the canes on your rose bush, that's a good sign that it's time to prune.
Roses should be planted in native soil, but require good drainage. You can mix some compost or other organic matter with the soil if you have poor, sandy soil or heavy clay. Add 2-4 inches of organic material and mix thoroughly into the garden bed at a depth of 12 inches.
Not enough water can cause your rose bush to get going slowly. Perhaps there was not much winter snow or precipitation, or not enough spring rains yet. If that is the case, start a weekly watering schedule early. If growth is slow in spring and you had a lot of dieback from winter, be sure to prune out all dead canes.
Generally speaking, you can expect your knock out® roses to last for 3 – 5 years – or blooming seasons. However, with some care in watering, fertilizing, and pruning, you can expect knockout roses to last several years. With proper care, they can potentially live for decades.