How To Take Care Of Knockout Roses?

Knockouts in Full Bloom
Knockouts in Full Bloom

Knockout roses have been a sensation ever since they got introduced, winning the AARS award in the year 2000. The features that make knockouts stand apart from other roses are as follows:

  1. They are extremely hardy
  2. They stay disease free
  3. Extremely undemanding and low-maintenance shrubs
  4. They are floriferous, blooming continuously well into the fall

Presently knockout roses come in 7 varieties – “Original knockout rose”, “Double knockout”, “Double pink knockout”, “Sunny knockout”, “Rainbow knockout”, “Pink knockout” and “The Blushing knockout”. The tips and suggestions mentioned in this article hold true for all of these varieties.

So you have purchased some knockout roses for your garden and now you are concerned about how to take care of them? Well, put your mind to rest for these are the most undemanding roses you will ever encounter. So to answer your question on how do I care for knockout roses, just follow these three steps.

  1. Plant them properly in a well-drained, rich soil
  2. Water them amply
  3. Provide them with adequate sun (min 6 hours of morning sun)
  4. Prune them once a year (start of growing season)
  5. Fertilize them a bit

It’s that simple! Knockout was developed to be disease resistant and low-maintenance and it stands true to these attributes. Only if you get really unlucky will you end up with some problems, in this article we will address in detail all the factors involved in taking care of knockout roses. This article provides information on knockout roses pruning, watering, fertilizing & disease control. Let’s start from the very basics of planting these shrubs in your garden.

How to plant & care for knockout roses?

There are basically three ways to grow knockout roses – in a container, in a flat garden soil bed, in a raised garden soil bed. The best way would be to use a raised garden bed since it has the best water drainage of the three. If you are using a flat bed make sure you place a mulch around the plant to improve water retention. Let’s discuss more on how to grow knockout roses.

When to plant knockout roses?

The answer would be “Anytime”. Knockout roses are so versatile that there can be grown anytime during the growing season. Most gardeners start planting them by start of spring. These rose shrubs will enter dormancy during the frost and start up again come spring. Knockout roses tolerate zone 4,5,6,7,8,9,10, so no worries about the zone you are in.

How to plant knockout roses in the garden soil?

If you have a bareroot knockout roses or if you are planning on transplanting a container rose plant onto the garden soil, just follow these three simple steps.

  1. Dip up the soil twice as wide and twice as deep as the root system of the bareroot plant or the size of the container.
  2. Add a layer of rich organic compost and peat moss at the bottom of the hole.
  3. Place the plant so that the knobby part of the stem is 1 inch above the soil level.
  4. Backfill with soil and firm it into place, soak thoroughly with water and backfill more soil to level it up.

Knockouts take easily to transplanting, in fact they don’t even shed their blooms in most cases.

How to space knockout roses?

Usually a spacing of 4 feet is recommended, the knockout rose shrub has a tendency to grow 3-4 feet tall and 3-4 feet wide given the right conditions. If you plan on spacing them closer let’s say 3 inches or less then you would need to prune them back to ensure they don’t cramp each other.

How to grow knockout roses in containers?

If you plan on growing knockout roses in containers just be sure that the soil depth and width allows the root system to develop properly. You should also ensure that soil is rich and drains well. Place the containers in a location which receives at least 6 hours of sun, especially the morning sun.

How to prune knockout roses?

Knockout roses do best when hard pruned. At the start of the growing season, on the day of the last frost, cut out the shrub to about 12 to 18 inches above the soil. Knockouts are fast growing shrubs and a hard pruning aids better growth and blossoms.

The most frequent concern is when to prune knockout roses? Without doubt it is always best to prune when the growing season starts (by the end of frost). Be sure not to prune the shrubs by the end of the growing season. This the time when the shrub would enter into dormancy and the last thing you want to do is disturb this state. It needs the leaves to enter into full dormancy.

Always make a cut at an angle of 45 degrees and use sharp shears or blades to do the job. A blunt tool causes more harm than good.

Deadheading knockout roses

There are two reasons to implement deadheading in general, firstly to ensure that the flower does not go to seed and secondly to ensure that the plant does not waste energy on a flower that is past its bloom. So do you deadhead knockout roses? Yes, mostly for the second reason. Knockouts don’t need to be deadheaded but it would certainly help improve the rate of blooms if you do it.

How often do you water knockout roses?

It is best to water deeply at least twice a week for best results. There is nothing more depressing than to see a flowering plant stop blossoming due to lack of water. Be sure to water at least 2 inches deep. Ensure that the soil is well-drained so it does not retain water on top.

You can use a soaker hose or drip irrigation to water knockout roses, but avoid spraying water on the foliage. Though knockouts are resistant to mildew and black spot it’s always a good practice to keep the foliage dry. For the same reason avoid watering in the evenings.

Water at the bottom of the shrub but avoid contact with the stem. Put a layer of mulch around the plant, it would help water retention. The mulch can be applied up 3 inches thick; you can use bark, cocoa, peat moss and straw for mulching.

How much sun do knockout roses require?

Knockout roses are very undemanding and easily make do with 5 to 6 hours of sun. Be sure to plant them in a location which receives morning sun directly. Knockouts don’t mind partial shade in the afternoon but morning sun is a must.

Should you fertilize knockout roses?

The first concern is, should I fertilize my knockout roses? The answer would be yes. Knockout roses do well when they are fertilized. What is the best fertilizer for knockout roses? Most gardeners have seen great results while using a 12-6-6 or a 10-20-10 fertilizer, a 1-2-1 ratio is preferred. It is common to use miracle grow for knockout roses, and it is hailed as the best fertilizer for this purpose.

The next concern is when do I fertilize knockout roses? In most cases fertilizing once every four to six weeks should do the job. Follow the instructions clearly so you don’t end up over fertilizing the soil. It is best to water the plant deeply a day before you intend to apply fertilizers. Avoid fertilizing on a hot day as it tends to burn up the plant especially if the conditions are dry.

How to prepare knockout roses for winter?

Rose shrubs enter dormancy with the start of frost when the soil becomes too cold. How to winterize knockout roses? Some gardeners use a burlap sack to cover the rose shrub in the winter to protect it from deers. You can also apply a mulch around the rose shrub to protect the top soil but be sure to apply it only after the plant has entered into dormancy and the frost is in full swing. If you place the mulch a little early you would end up warming the soil which would cause the rose shrubs to stop going into dormancy. Though it’s a perennial lifespan of knockout roses is not restricted, due to its hardiness and drought tolerance these shrubs have the tendency to last for several years.

Common Problems With Knockout Roses

Aphids on Knockout Roses
Aphids on Knockout Roses

Knockout roses were bred to be disease resistant and they stand true to their breeding. They are low maintenance plants and rarely bother you with pest or fungi problems but there are certain exceptions to the rule. Depending on your climate, fertilizing efforts and watering practices your knockouts might end up with a few problems.

What insects attack knockout roses?

The most common insect to attack knockout roses would be aphids. These critters more likely than not would end up on the stems and branches of your knockouts come spring time. Aphids don’t cause any problems with knockout roses expect a cosmetic one. The best way to deal with aphids is to squish them manually and dip them in a soap solution to be disposed. The second best thing to do would be to treat them to a hard burst of spray from the water hose. Avoid using pesticides to deal with aphids as it would harm the rose shrub and make it more susceptible to an attack by spider mites (they are more difficult to handle).

How to keep knockout roses insect free? Well the best practice involved in bug care for knockout roses are mentioned below

  1. Get rid of dead or infected braches and leaves on prompt basis. Maintaining plant hygiene would go a long way in keeping it insect free.
  2. Avoid watering the foliage and the stem
  3. Allow a good air flow between plants instead of cramping them up.
  4. Apply fertilizers on timely basis and keep the water amply watered
  5. Kill the bugs manually as much as possible and avoid the use of insecticides unless the infestation is out of control.

What diseases are knockout roses prone to?

Though these shrubs are bred to be disease resistant your knockouts may get unlucky at times and get infested by one of the below diseases.

1. Black spot

If the humidity in your garden stays high through out and the temperature is around 75 F, it provides conditions for development of black spot on the rose shrubs. It starts with small black spots on the leaves which turn to yellow rings and eventually turn the entire leaf yellow. So if you end up with yellow leaves on knockout roses it would have to be a black spot attack.

2. Mildew

High humidity and moist conditions on the leaves result in mildew, it manifest as white powdery substance that covers the leaves. If the foliage is untreated it would shrivel up and fall off. So if you are wondering why are there white spots on the leaves of my knockout roses? The culprit is mildew.

3. Rust

A fungal infection which results in reddish orange spots appearing on the leaves of the rose shrub. Cool and moist conditions result in rust formation. The infected plant would end up defoliating with time if left untreated. So if you are asking why are the leaves of my knockout roses turning red? The villain could well be rust.

Knockout roses are disease resistant, so it would be quite rare to observe these diseases but a few good practices definitely help.

  1. Avoid watering in the evening
  2. To keep the foliage dry use a soaker hose instead of a sprinkler
  3. Allow for good air circulation
  4. Remove the dead limbs, flowers and leaves on timely basis
  5. Infected parts should be cut off immediately
  6. Treat the plant with a sulfur or fungicidal soap spray in case of infection

Most likely than not you will not end up with any problems with knockout roses you plant, especially with respect to leaf diseases. If you follow the above guidelines you will further reduce the rare possibility of ever encountering black spot, rust or mildew.

Leave a Comment