If you’ve ever grown roses, you know how much work they can be. Luckily, knock out roses are the exception! They’re the gardener’s dream come true. Knockout roses are tough, disease resistant, low maintenance, and bloom all season long. Whether you’re a rose beginner or a garden pro, these roses can be a great addition to your garden. So, when’s the best time to plant knockout roses?
Knockout roses are typically planted in early spring, a few weeks after the season’s final frost. This is usually sometime between mid-March and late April, but it could be as early as February in warmer areas. Check the forecast to make sure no frost is expected in the next couple of weeks.
Knockout roses are among the most popular shrubs grown across the US. In fact, you’d be hard-pressed to find a nursery or garden center that doesn’t sell them in some form or another. Let’s find out more about planting knockout roses, including why they’re so popular and some tips to get the best out of them.
What Are Knockout Roses?
William Radler, a former horticulturist from Wisconsin, bred the first knockout rose (called RADrazzz) in 1989. It was a low-maintenance, disease-resistant rose that bloomed all season long with very little care.
It was an instant hit, and by 2000, knockout roses became the top-selling shrub in the US — a trend that still continues to this day.
There are now over ten varieties of knockout roses in different colors and bloom sizes. But they all have one thing in common — they’re tough as nails and super easy to grow!
Knockout roses (on Amazon) are hardy in USDA zones 4-9 and bloom Spring through Fall. They resist common rose pests and diseases like black spots, powdery mildew, and Japanese beetles. One exception is the rose rosette disease, which, unfortunately, has no known cure.
They also don’t need to be deadheaded (the process of removing spent blooms) like traditional roses, which makes them super low maintenance. Just plant and forget — it’s that easy!
When’s the Best Time to Plant Knockout Roses?
The best time to plant knockout roses is in the spring, after the last frost. You can also plant them in late fall, as long as the temperatures are above freezing.
If you live in a warmer climate, you can plant knockout roses year-round. Ideally, the soil temperature should be between 65 and 70℉ (15-21℃), so they can establish roots before the hot summer weather hits.
If you have bare root roses, it’s better to plant them earlier in the season while potted plants can go in later.
In What Temperatures Do Knockout Roses Grow Best?
Knockout roses are hardy in USDA zones 4-9, which means they’re tolerant to a wide range of temperatures. However, they grow most comfortably in warm weather and will bloom best in temperatures between 65 and 70℉ (15-21℃).
These roses will still bloom in colder weather, down to 10℉ (12℃), without any protection. With some insulation like frost covers (on Amazon), they can even survive in temperatures as low as -20℉ (-29℃). However, they’re still vulnerable to frost if the temperatures drop too quickly.
On the other hand, knockout roses can also tolerate hot weather of up to 100℉ (38℃) as long as they’re watered regularly.
Preparing Your Garden
When you’re ready to plant, the first thing you need to do is choose a spot in your garden that gets at least 6 hours of sunlight a day. Though they can tolerate shade, the best bloom comes in full sun.
Knockout roses are tolerant to a wide range of soil types, from sand to clay. The important thing is that the soil is well-drained; they can’t tolerate soggy or wet soils. To improve drainage, use a spade or tiller to loosen the top 6-8 inches of soil and mix in organic matter like compost or manure.
If your soil is particularly heavy, you can mix in some perlite (on Amazon) or sand to lighten it up. Then, mound the soil up about 6 inches to create a raised bed, this will also help with drainage.
One knockout rose plant can take up to 3 square feet, so make sure you have enough space for all the plants you want to add to your garden.
You might also need to amend the soil to get the right pH level. Knockout roses prefer slightly acidic soils with a pH between 6.0 and 6.5. A soil test kit (on Amazon) can help you determine the pH level of your soil. You can lower it by mixing in some sulfur if it’s too high. If it’s too low, you can raise it by mixing in some lime.
You don’t need to fertilize your knockout roses until they’ve been established for a few weeks or months. Once they start blooming, you can fertilize them every six weeks with rose food or a general-purpose fertilizer.
Do Knockout Roses Require Less Maintenance Than Typical Roses?
Absolutely! One of the reasons why knockout roses are so popular is because they require very little maintenance.
Roses are notoriously high-maintenance plants, but knockout roses, according to their creator, William Radler, “don’t know they’re roses.” Here’s what that means:
- Roses get attacked by all sorts of pests and diseases. Black spots and powdery mildew are particularly well-known for ruining many a rose garden. Knockout roses are resistant to these and many other common rose problems, so you can enjoy your roses without all the spraying and fussing.
- They don’t need to be pruned as often as other roses. You can prune them in late winter or early spring, just before they start to bloom. Otherwise, you can let them grow naturally and only prune them if they start to get too big or leggy.
- They’re self-cleaning, so you don’t have to deadhead them. Deadheading is the process of removing spent blooms from the plant. With other roses, you need to do this regularly to encourage more blooming. But with knockout roses, the spent blooms will drop off on their own.
- They’re drought tolerant. Once they’re established, they can go weeks without being watered. Still, they will bloom best if you water them regularly, especially during hot weather.
- Knockout aren’t heavy feeders. In fact, you should not fertilize them until they’ve established themselves in your garden. After that, an occasional dose of organic liquid fertilizer (on Amazon) or granular 10-20-10 fertilizer is all they need to stay healthy and bloom well.
Tips for Avoiding Pests and Disease
Despite their resistance to many common problems, knockout roses can still be susceptible to pests and disease. To keep your plant completely healthy, follow these tips:
- Don’t plant your roses too close together. Knockout roses have dense foliage and need good air circulation to stay healthy. Planting them too close together can lead to poor air circulation and increased disease risk.
- Don’t water from above; wet foliage can attract fungal diseases. Water the roots directly, either with a soaker hose or drip irrigation (on Amazon). Water early in the morning, so the wet part of the plant dries out before nightfall.
- When fertilizing the plant, ensure it doesn’t touch the foliage — this can damage/burn the plant, creating a welcome sign for pests and diseases.
- Prune off any diseased leaves or stems and dispose of them properly. These can harbor pests and diseases.
- If you see any signs of disease, such as a black spot or powdery mildew, treat it immediately. Don’t depend on the plant’s resistance; instead, use appropriate fungicide or other methods to nip the problem in the bud.
- Pests are less of a problem with knockout roses than with other types, but you may still see the occasional aphid or Japanese beetle. Knock them off with a blast of water from the hose or pick them off by hand and drop them into soapy water.
- Maintain 3-4 inches of mulch around the base of the plant. This will help deter weeds and keep the plant healthy to fight pests and diseases.