Tips On Fertilizing Knockout Roses: When and What Kind?

Pinterest Hidden Image

The patented Knock Out Rose is a family of compact rose bushes and a few tree variants best known for their low maintenance requirements (self-cleaning) and disease resistance. The red flower-colored Knockout first hit the market in the year 2000.

Knock Out roses grow best in USDA hardiness zones 5 to 9. The common shrub version reaches a width of 3′ to 4′ feet.

Red Knock Out Roses in bloomPin
Flowering Red Knock Out Roses | BryanPollardPhotos-DepositPhotos

These new plants grow in almost any location. Unlike normal roses, they tend to thrive in poorer conditions than their kin. 

Knockouts like full sun, so make sure it’s in a spot that receives at least 6 hours of sunlight daily.

It is not necessary to deadhead flowers to encourage new growth, but maintaining proper care, such as plenty of sunlight, moist soil, and adequate fertilization, will help protect the plant’s flowers and foliage.

When growing roses in containers, leave the plant outdoors for the season’s first frost to help it adjust to dormancy.

Sometimes referred to as Knockout Rose, there are currently 11 official Knock Out Rose varieties in a range of colors:

  • ‘Meibenbino’ – dwarf, bright red
  • ‘Radcon’ – (Pink Knock Out) bright pink
  • ‘Radcor’ – (Rainbow Knock Out) coral with yellow center
  • ‘Radgor’ – (Peachy Knock Out) shell pink petals with yellow center
  • ‘Radral’ – brick orange fading to coral
  • ‘Radrazz’ – original red-to-pink variety
  • ‘Radsunny’ – (Sunny Knock Out) yellow that fades to cream
  • ‘Radtko’ – red double-flowers
  • ‘Radtkopink’ – pink double-flowers
  • ‘Radwhite’ – white
  • ‘Radyod’ – light pink

These roses do not require fertilizing (except for tree varieties). But fertilizing knockout roses will encourage healthy plants and more vibrant growth.

Related: When and How Long Knock Out Roses Bloom?

Best Rose Fertilizer For Knock-Outs

As a general rule, a 6-12-6 NPK mix is ideal for any landscape roses, but this ratio isn’t common on the market. Nitrogen is the first 6, 12 is for phosphorus, and 6 is for potassium.

Thankfully, the Knock Out Rose does fine with a balanced formula and will tolerate a wider range of mixes.

For the best results, check your soil’s nutrient levels, either on the package or using a test kit.

Go with a commercial slow-release fertilizer that best meets the deficiencies of your soil.

Here are three great commercial products that will all work well with your Knock Out Roses.

A vibrant pink Knockout rose in full bloom, with multiple layers of petals and a yellow center.Pin

Burpee Organic Rose and Bloom Granular Plant Food

The Burpee organic fertilizer is OMRI-approved (Organic Materials Review Institute). The food comes in a granular form providing rose plants with slow-releasing nutrients.

Its 4-6-4 NPK ratio is well-balanced and works well on any rose.

Jobe’s 9429W Knock-Out Rose Organic Granular Fertilizer

While not one of the bigger names, this fertilizer is also OMRI-approved. This fertilizer contains a 3-4-3 NPK ratio along with other important nutrients.

This fertilizer is formulated for Knock Out Roses. It also contains beneficial bacteria that aid in preventing infections, pest problems, and rose diseases.

Unfortunately, knockout roses are susceptible to aphids, thrips, Japanese beetles, sawflies, or Rose slugs.

Healthy roses not only bloom better, but they are also better able to withstand insect and disease problems like black spots, rust, and powdery mildew. Plus, the need for any sulfur sprays or insecticides is reduced.

Spraying the foliage with a jet of water also works because spider mites love dry foliage and hate wet foliage.

Miracle-Gro Water-Soluble Rose Plant Food

One of the most famous brands is a house plant, vegetable garden, and rose care.

This newer liquid fertilizer formula has an 18-24-16 NPK ratio to encourage growth and longer-lasting blooms.

Only a small amount is needed (one tablespoon per gallon of water, to be precise). It is easy to apply as specified when watering your plant.

Details on:

When Or How To Fertilize Double Knock Out Rose

As mentioned, Knock Out Roses generally don’t need fertilizer. But there are times when you’ll want to feed them for better growth.

Under no circumstances should you fertilize your Double Knock Out Roses until after the first bloom cycle! This could severely damage the plant.

Fertilizing A Rose Knock Out Shrub Rose

Always water your rose before feeding but avoid overhead watering. When plants have good soil moisture, it reduces the possibility of chemical root burn.

Use one of the fertilizers mentioned above. Follow the instructions on its label.

As the growing season starts, fertilize only in the early spring (April) and early summer. In late summer, your Knock Out rose will be preparing for the winter. Feeding could result in vulnerable new growth.

Two blooming Knockout bushes with vibrant red flowers.Pin

Late in the summer (August or September) is not a good time to fertilize roses. This is because this will cause them to grow new shoots that will die off with the first hard frost.

When applying fertilizer, make sure the soil is moist. Apply the fertilizer to the ground around the plant, not at the base of the plant, and never to the leaves, canes, or stems of the plant. This can burn the plants and even cause them to die!

 If you are uncertain about soil drainage in the area where you intend to plant your roses, it’s well worth testing the drainage before planting.

Fertilizing a Tree Knock Out Rose

Unlike the shrub version, Knock Out Rose trees need plenty of organic nutrients to thrive.

You will want to mix rich organic matter into the soil, such as compost or manure and coffee grounds.

Add mulch every spring and early fall, mixing in more organic material.

After the spring mulching, start pruning back any thin canes at the bottom. Trim back any larger healthy ones to allow better plant growth with its fresh meal.               

When Knock Out rose bush pruning, you can reduce the bush size by ⅓ once a year to open up the center and create a large, healthy rose bush.     

JOIN Our FREE Plant Care Newsletter 

By entering your email address you agree to receive a daily email newsletter from Plant Care Today. We'll respect your privacy and unsubscribe at any time.