No one appreciates the joy and frustrations of gardening more than we do here at Gardening Know How. Because of this, we strive to help our fellow gardeners in need whenever possible by providing answers to questions about your most prized plants, of which includes rose bushes. Below are the 10 most commonly asked questions about roses that we encounter.
Black spot is a common fungal disease of roses. Spores of the fungus Diplocarpon rosae can seem to infect whole plants overnight in wet, humid spring weather. Black spot starts out, as the name suggests, with black spots on the foliage. Foliage will then become mottled with yellow and drop off the plant. Stems may also have black and purple spots. Being infected by black spot can weaken the plant and deprive it of nutrients, leaving it more susceptible to other diseases or pests. To treat black spot, prune off all infected stems and foliage. Then spray all the remaining parts of the plant with a fungicide like neem oil or copper fungicide. Many of the products made specifically for rose care will contain a fungicide. For prevention, treat roses with a fungicide in spring before prime conditions for spore growth happens, which is generally when temperatures stay consistently around 70 degrees F. (21 C.) and are damp.
If roses need to be transplanted, this should be done in early spring before they leaf out. When transplanting anything, pre-dig a large hole where the plant will be going before digging up the plant. This will reduce transplant shock and allow you to investigate the soil in the new site and make amendments if necessary. You can also mix up a batch of water and rooting fertilizer to help the plant adjust to its new home. It also helps to prune back the rose to a height of about a foot; this will cause the plant to put more energy into rooting than leafing and budding. It also eliminates some of the thorns, which can make working with roses unpleasant. Dig up the rose bush, taking care to get as much of the root structure still intact. Plant in its new location no deeper than it was planted previously. Refill the hole at soil level with a mixture of water (and rooting fertilizer if desired). Water daily for the first week, every other day the second week and then once a week for the rest of the growing season.
Pruning roses is not as complex as it is sometimes made out to be. In general, roses are not nearly as fussy as people think. When cutting back, pruning or deadheading roses, always use clean, sharp pruners. Make cuts at a 45-degree angle just above a leaf set. Major cutting back of a rose bush should be done in late fall or early spring while the plant is dormant. Deadheading or cosmetic pruning can be done at any time, as needed. Roses will benefit from a good hard pruning once a year.
There can be many reasons a rose may not bloom. One cause could be too much nitrogen in the soil or fertilizer you are using. Nitrogen promotes lush, green foliage and can cause the plant to put all its energy into the foliage, not blooms. Fertilize roses with a fertilizer made specifically for roses for optimum health and growth. Not enough sunlight can also cause roses not to bloom. Roses need at least six hours of sun each day. Insects or disease can make a rose not bloom. For best results, use a systemic 3-in-1 rose treatment on roses that contains rose fertilizer, pesticide and fungicide in the spring.
Roses can be susceptible to many diseases. Both Bayer and Bonide make 3-in-1 systemic rose products that have rose food, pesticide and fungicide. I treat my roses each year with a 3-in-1 systemic product like this to prevent diseases and pests. Systemic products are watered in at the root zone and then they take time to work their way throughout the plant. There are also many available ready to use sprays for fungal diseases of roses, like neem oil, copper fungicide or Bayer’s rose and flower spray. Always follow directions on product labels. It is also a good idea to cut back any diseased tissues of the plant and dispose of them immediately, then treat the plant.
Aphids are common pests of roses. Many pesticides you can buy for roses will kill aphids. Neem oil works on rose pests like this as well as fungal diseases. You can also make a homemade pesticide by mixing one part blue Dawn dish soap, one part mouthwash and four parts water. Spray this on a cloudy or overcast day, making sure to spray the undersides of the leaves and any other places aphids may be hiding. Another non chemical solution for aphids is to plant a decoy plant near your roses that will attract the aphids. Goldenrod or milkweed work well as aphid decoy plants.
Planting bare root roses is not much different than planting a purchased potted plant. Dig a wide hole, deep enough to accommodate the bare root rose’s stubby roots. It helps to make a mound of dirt in the center of the hole. Place the bare root plant on the mound of soil and hold it upright as you back fill the hole, tamping down the soil lightly as you go to prevent air pockets that may make it lopsided later. Do not plant the bare root rose too deep, only the roots should be under the surface of the soil. Water deeply and thoroughly, with a rooting fertilizer if you choose. Water every day for the first week, every other day the second week and then 1-2 times a week for the rest of its first growing season.
These days there are hundreds of specialty rose foods on the market. Most are comprised of many of the same ingredients and NPK ratio. In spring, I like to feed my roses with a systemic 2-in-1 product that contains fertilizer and pesticide. Roses often require extra phosphorus, so I also treat mine with bone meal in midsummer. Fertilizers that contain high nitrogen, the N in NPK, can cause roses to be green and leafy but not bloom properly. When fertilizing roses, try to find a rose food with a higher middle number, like 10-15-10. Spring is usually a good time for fertilizing roses.
Winterizing roses depends on which climate zone you live in. In cooler northern climates, the roots and crown of roses may need extra winter protection. Organic mulches are the best way to give roses added insulation through winter. Rose cones can cause roses to warm up too much on mild winter days. This freezing, then thawing, then refreezing can cause damage or even death to roses. Instead, heap about 6-12 inches of organic mulch over rose bush roots and crown in late fall. This is referred to as mounding and will typically provide enough protection for the plants over winter.
Yellowing foliage on roses is oftentimes a symptom of black spot or another fungal disease. It may be necessary to cut back this yellowing foliage, disposing of it immediately to not spread the disease further, and then treat the whole rose plant with a fungicide like neem oil. Yellowing foliage can also be a sign of a nutrient deficiency. Usually, nitrogen is what keeps foliage green and healthy. Nitrogen is also very easily leached out of soil by repeat watering or frequent rain. If you suspect that your roses are deficient of nitrogen, give them a dose of fertilizer with a higher first number, like 10-4-5.
Everyone has questions now and then, whether long-time gardeners or those just starting out. So if you have a gardening question, get a gardening answer. We’re always here to help.