Knockout roses are a relatively new perennial that’s making waves in the gardening community. I’ve seen success with traditional garden roses in the past. But with this revolutionary variety, I wanted to see if container gardening was possible.
You can plant knockout roses in container but choose one that is at least 16-inches deep. A 10-gallon, ceramic or terracotta container is a good choice as this plant is top-heavy. You’ll get the best flowers in the second or third year of growing them in the container.
I researched how to plant knockout roses in containers and created this step-by-step guide to show you what I learned.
Choosing the Best Time to Grow
Knockout roses are a hardy perennial. Developed in the 1970s, they officially hit the scene in 1999. Knockouts are a unique plant that addresses many of the problems that gardeners have with heirloom varieties. Available at nurseries around the globe, these plants make it easy to enjoy the fragrant blooms of roses all to yourself.
The first step in planting Knockout roses is to plan ahead. These roses are hardy enough to handle planting at any point during the spring and fall. But if you want to start your plant on the right foot, wait until late winter.
Planting between late winter early spring gives your rose shrub a better chance at success. It gives the plant more time to establish itself in the new environment. You won’t notice much growth until spring rolls around. But hose extra weeks in the soil will make a huge difference once the sweltering heat of summer kicks in.
There’s a bit more wiggle room with container planting. You can still get good results if you wait until early spring. But, earlier is always better.
Where Do Knockout Roses Grow?
Knockout Roses are surprisingly hardy. As a result, they can often flourish in places where standard roses die off.
These plants do best in USDA hardiness zones 5 through 10. They resist both harsh cold and excessive heat. Some gardeners have had good results further north than recommended. The plant can reportedly withstand temperatures as low as 10 degrees.
If you live in an area with tough winters, you can bring the rose inside. Like any other rose bush, Knockouts go dormant during the winter. Bringing them inside can prevent permanent damage due to excessive frost and freezing.
Understand How Long it Will Take to Grow
One of the biggest perks of Knockout roses is their fast-growing nature. Whether you plant from a cutting or rootstock, it doesn’t take long for you to start seeing those precious blooms.
Generally, it will take several months for the plant to get comfortable in the pot. Don’t expect to see much action outside of the soil. This is especially true when you plan in the winter. However, underneath the soil, the plant is working hard to develop new growth.
In the early spring, you should start to see new growth. Within a month or two, the first blooms should appear.
Like most shrub rose varieties, Knockouts are fully capable of producing flowers during the first year. However, it’s going to be a couple of years until you see the plant’s full potential. As the plant matures and winters over, it will get stronger and more capable.
Knockout roses can reach heights of three to four feet tall. They are equally wide, resulting in a voluminous shrub that will look great in a sturdy container. You can also train some varieties to grow in a tree-like form. Either way, the plant should reach its full size within three or four years.
What About Dormancy?
As mentioned earlier, Knockout roses do go dormant once the temperature drops. Depending on where you live, this can happen in the late fall or early winter.
When the plant goes dormant, it will drop all of its foliage, resulting in a barren-looking plant. Don’t worry: Your plant is not dead.
Dormancy is a critical survival technique. The sap within the cells of your rose shrub thickens, providing ample protection from freezing temperatures. During this time, the plant will reserve its energy and come back once temperatures rise again.
Choose the Right Container for Knockout Roses
Once you have your timing all planned out, you can move onto choosing the right container.
Root depth varies for this plant. It all depends on the age of the plant and the density of your soil. Knockouts are adaptable enough to accommodate the growing environment.
That said, you should aim for a large pot with ample depth. A 10 or 15-gallon container is ideal. Make sure to check the measurements. Go for a container that’s at least 18 inches in diameter and 16 inches deep. If you can go larger, do so. These plants like to spread their roots if there’s adequate room.
Design and Material Considerations
Usually, the design of your container is all a matter of personal preference. But with Knockout roses, the type of pot you choose has a greater impact.
You see, Knockouts tend to get a bit top-heavy. As the blooms come in, the weight of the flowers and foliage could easily cause your pot to tip over. Remember, these plants have a wide spread even in containers.
To ensure that your plant is safe and secure, choose a hefty pot with some considerable weight. Terracotta, ceramic, and concrete planters are all good choices. Plastic is a good temporary solution, but there’s always the risk of a heavy wind knocking it over.
The final consideration is drainage. Knockout roses will not tolerate standing water, so your container should have several drainage holes on the bottom.
Standing water will damage the root system. It could lead to root rot, pest infestations, and a host of other health problems.
If your pot doesn’t have enough, take a drill to it.
Prepare the Container for Planting
When it comes time to plant, there’s still some prep work to do.
In addition to creating drainage holes, you need to find a way to prop your pot up. One of the biggest mistakes that novice gardeners make is setting the container directly on the ground or concrete. When you do that, you’re essentially blocking the drainage holes.
Use a lifted container tray or a decorative stand. You can also use something as simple as a few bricks. Whatever the case may be, make sure that the drainage holes are open and ready to release water.
Some gardeners choose to add rocks or pebbles to the bottom of the container. This is a viable choice, too. It can add significant weight to the pot and improve soil drainage. However, those rocks will take away valuable space for the rose’s root system.
Knockout roses need nutrient-rich soil that drains well. Loamy soil is one of the best choices. It shouldn’t be overly sandy or have too much clay. Ideally, the soil should hold onto moisture well while still letting some of that excess water flow out through the drainage holes.
Work the soil thoroughly with your hands or a garden trowel. The goal here is to remove any lumps and avoid compaction.
While you’re at it, throw in some compost. Organic compost can do wonders to support your plant in the years to come. Container flowers are notorious for leaching all of the nutrients out of the soil after a few years. Infusing it with compost early on will help maintain soil conditions. Plus, it gives your Knockout rose shrub the kick it needs to start off strong.
For pH, aim for levels between 6.0 to 7.0. These roses like things relatively neutral if not a hair on the acidic side. If the soil is too alkali, add some peat moss. You’ll want to do this several months early to ensure that pH levels are correct when it comes time to plant.
Plant the Seeds, Seedlings, or Cuttings
Finally, it’s time to get planting.
Knockout roses come in a couple of different forms. However, the planting process is relatively the same.
Interestingly enough, Knockouts aren’t available in seed form. If you want to grow from seed, you’re going to have to pay a little more and get special permission from the developer.
That’s because Knockout Roses are a patented product. The original seller of these plants, Star Roses and Plants, owns the rights to the plant. Planting seeds or cuttings would be infringing on the patent. While it might not seem like a big deal, the patent-owners have gone after gardeners in the past. It’s not something you want to get mixed up in, so make sure that you’re getting an official container plant or bare-root from a reputable seller.
Planting Bare-Root Roses
Available from many nurseries, bare-root plants give you a bit more flexibility with planting. As the name would suggest, this form is nothing more than a bare root without any soil.
Analyze the size of the root ball. Then, dig a hole in the soil that’s about three times the size. Gently place the root into the hole and lightly pack the soil around it for security.
Make note of any grafted unions. If the root has a visible graft, make sure that it’s planted one to two inches below the top of the soil. Otherwise, there’s a risk of rot and disease.
Planting Young Container Plants
Purchasing young container plants is the easiest option. These plants are semi-established. However, they are still delicate and require additional growth before blooming.
The planting process is basically transplantation. Dig a hole that’s roughly the same size as the existing container. Then, gently remove the soil and root mass. You can loosen the soil a bit to make things easier for the root to spread beyond it. Pack it in at the same height and you’re good to go.
Provide the Required Sunlight
Ample sunlight is a must for Knockout Roses. These plants need plenty of energy to grow in the early stages. Transplant shock is a real issue to be wary of. So, you need to place your newly planted rose shrub in a spot that provides as much light as possible.
Knockout roses need six to eight hours of sun every day. The more sun the plant gets, the better. High sun exposure promotes stronger growth, which could result in more bountiful blooms.
When Does the Knockout Rose Bloom
With the right amount of sun, these roses will start blooming pretty quickly. A bloom cycle lasts for about five to six weeks.
However, Knockouts don’t just bloom once. In temperate climates, they can go through upwards of seven bloom cycles in a single year. They will continually produce flowers from mid-spring to fall as long as the temperature is right.
Sun exposure plays a big role in how often buds form. Oftentimes, the blooming cycles will occur in waves. You might see a big burst of flowers during the cycle. Then, a steep decline will follow with only a few blooms here and there before the next cycle occurs.
However, lots of sun can help fill in the gaps between cycles. The more exposure your plant gets, the more energy it has to develop those sought-after buds.
Water the Knockout Rose Plant
Knockout roses are resilient plants. But, they can only stay beautiful and hardy if they’re getting enough water.
It’s best to water these plants every few days to ensure that the soil stays moist.
The key to watering these plants is to let them drink slowly and deeply. The goal is to let the water soak deep into the soil so that the root system has an easier time absorbing it. Provide a large volume of water so that the soil is moist 12 to 18 inches down.
You can water the plant the old-fashioned way with a watering pale. But if you have several potted shrubs, it may be better to use a soaker hose. A soaker hose will release water slowly, allowing it to penetrate deep. Not only that, but the hose will prevent accidental splashing.
It’s important to avoid getting water or mud on the foliage. Doing so could lead to fungal problems, mold, and scorching from the sun.
When to Water Knockout Roses
Aim to water your roses in the early morning. This will give the water a chance to fully soak into the soil before the sun rises high above the plant. Avoid late evening and midday waterings.
Late waterings don’t give the water enough time to drain and evaporate. As a result, the roots can become waterlogged and overly saturated. With midday waterings, you’ll have the exact opposite problem. The temperatures are too high, resulting in quick evaporation instead of a slow soak.
If you experience a particularly dry week with no rain, consider giving the plant a few extra inches of water during the week. You can do this over the course of several days to prevent overwatering issues.
Mulching may be beneficial in hotter climates. Spread two to three inches of mulch on top of the soil. Make sure to leave some space around the base of the plant.
The mulch will help retain some moisture and avoid quick evaporation. It can also regulate soil temperatures to keep things on the cooler side.
Prune the Knockout Rose Plant
While Knockout roses are pretty low-maintenance, they can still use occasional pruning.
Pruning helps to divert the plant’s energy and manage its growth.
There are a few different times to prune.
The first, and most crucial, is going to be in the early spring. This pruning job is all about maintaining the plant’s size. If you don’t prune, the shrub can become overgrown and unmanageable.
Cut the plant back to about 12 inches after the last hard frost of the year. It looks dramatic, but don’t worry. Pruned Knockout roses will triple in size after your prune. By the end of the year, it’ll be back to the pre-prune height.
Use sharp pruning shears to cut the branches at an angle. Discard the debris and give the plant a good watering to help it recover.
You can also prune the plant several times throughout the year. These shrubs are fast-growing, so some ongoing maintenance is always a plus.
Mid-season prunes focus on reducing density and encouraging healthy growth. The best time to do this task is during that plant’s resting phase.
Remember how I said that the plant goes through several blooming cycles throughout the year? Well, the resting phase is those in-between weeks where flowers are sparse and new buds haven’t come to fruition just yet.
Use this time to cut off small or damaged canes. Examine the branch structure closely and make adjustments to super-dense areas. You want to improve airflow a bit and give the branches room to breathe. Use hand pruners here and be gentle.
When to Stop Pruning
Prune as much as you need during the spring and early summer. But, stop all pruning activities in the latter part of summer or early fall.
At this stage, your plant is winding down. But if you continue pruning, you’re just going to encourage more growth. This could impact the dormancy cycle and prevent the plant from hardening off before the winter.
If you need to do some additional pruning, you can cut old branches off during the winter. However, only do this if you live in the warm South. The harsh temperatures of northern winters will do some damage if you prune. It’s best to wait until things warm up after the last hard frost.
What About Deadheading?
Deadheading is the process of removing spent flowers and buds.
Usually, this process is necessary to promote continued growth. But for Knockout roses, it’s not a requirement. These plants are self-cleaning, so you can just leave the plant alone and watch new blooms come in.
That said, deadheading won’t do any harm. The process can create a tidier look, which is always a good thing.
Fertilize the Knockout Rose Plant
Knockout roses do just fine without fertilizers. If you mixed in some compost before planting, your shrub should have all the nutrients it needs for at least a year or two.
Of course, an extra boost of nutrients can help your plant reach its full potential. It’s all a matter of personal preference.
If you do want to go this route, you need to plan your applications accordingly.
The most important thing is to wait until after the first bloom cycle. The plant should be well-established before you attempt to feed it any form of fertilizer. Applying too early could lead to development issues.
After that first wave of flowers, you can apply a standard balanced fertilizer product. I recommend using a simple water-soluble formula for simplicity. Prepare the mixture according to the instructions and apply it slowly to the soil around the base.
Make sure that you water your plant first to avoid burn. Also, pour the product slowly to ensure that you don’t splash any fertilizer onto the stem.
You can apply fertilizer three or four times during the spring and early summer.
But like pruning, you need to stop in the latter part of summer. You don’t want to create any unnecessary growth as your plant prepares to go dormant for winter.