It’s probably happened to everyone who has cultivated roses for a while. You put the rose into the ground at the right time of year. You follow the planting directions scrupulously. You keep the rose watered as it sets leaves and makes canes. You fertilize it. And the first year … nothing. So the next year you prune it and fertilize it some more. And still nothing. The rose doesn’t bloom.
There are lots of places on-line where people complain of the problem, but few places undertake to list all the causes. Here’s a pretty complete list to consider if your rose fails to bloom.
- Light – Your rose should get at least six hours of direct, unfiltered light. Some hybrid teas need more than eight to bloom. A few old roses and hybrid musks might get by on just a bit less. Lack of light is the leading cause of failure to bloom in roses.
- Water – Soil at six inches and deeper (established roses) should not dry out. Some well-established plants do fine through long dry spells; but repeating roses that fail to bloom in summer or fall might sometimes be reacting to stress from drought. Give them a deep, slow watering. A rule of thumb is an inch of water per week. Twice that when the temperature is over 90F for most of the day.
- Standard Nutrition – Fertilize with an organic fertilizer such as Mills Magic. Or use a slow-release fertilizer like Osmocote. Too much nitrogen will cause growth at the expense of bloom.
- Non-Standard Nutrition – Have your soil checked, and have it amended to fix imbalances. Some advocate administering bone meal, or epsom salts, or potassium-magnesium sulfate to encourage bloom, a tablespoon at a time.
- Bud Union – If it’s a grafted rose, check the bud union. Sometimes a graft is bad or the scion dies and the rootstock pushes up: and sometimes rootstock doesn’t bloom very well.
- Pruning – Pruning the wrong way can have a negative effect on blooming. Prune once-blooming roses within a few weeks of when they have bloomed. Prune repeat-flowering roses such as floribundas and hybrid tea roses in spring before they start to leaf out. If you live in a place with a lot of freezing and thawing in spring, you may want to delay doing this until hard frosts have passed – especially with frost-tender plants. Bear in mind that different rose cultivars respond to pruning differently. While many hybrid tea roses and floribundas might be invigorated by heavy pruning, some tea roses and other old roses might sulk or give up. Seek advice about your rose cultivar at a place like HelpMeFind roses before pruning hard.
- Frost – Late frosts can kill rose plants. Or they can freeze spring rose buds. By planting cold hardy roses this effect can sometimes be ameliorated. It is possible, too, that applying a few extra inches of mulch will slow the warming of the soil, possibly delaying bud development just a tiny bit.
- Training – Climbing roses, bourbon roses, hybrid perpetual roses, and some other roses make strongly vertical growth and will typically bloom at the end of a vertical shoot. Train canes at a more horizontal angle, about 45 degrees, or peg the long cane to the ground. This causes them to make ‘laterals’ and these lateral branches each form a bloom. The number of blossoms formed by a long cane may be multiplied by ten or twenty or more using this method. And the rose likes it.
- Disease – Serious infestations of blackspot or mildew will weaken a rose, and the effects can sometimes carry over into the next season. If your rose spends more than a week or two defoliated during the growing season thanks to fungal infection, this could be weakening the rose to the point it will not bloom. Only if you get the infection under control will it perform better. Sometimes PNRV or some other viral or bacterial infection will weaken a rose, too.
- Pests – Serious infestations of pests can weaken a rose, too. Most pests don’t do serious damage, and the ones that do generally kill the rose. Japanese beetles or pocket gophers can nibble a rose to death. Trapping can sometimes help here. Deer can nibble young roses to death; they also like to feast on rose blossoms. High fences can help. Thrips can suck all the vital fluids from a rose bud and prevent it from opening. A solution is to plant a trap plant such as Lagerfeld. If that’s not enough, dust Lagerfeld’s blossoms with rotenone or pyrethrum during thrips season in spring.
- Check References – Some roses can take up to five years or more to get established, Sunset Celebration, for example. Others put a lot of energy into making a few roses, Parole, for example. Still others are just stingy. Remember, too, that not all roses are remontant; some only bloom in spring or summer. Check ARS Handbook for Selecting Roses, or the online resource HelpMeFind.
Once all these possibilities have been exhausted and the rose is still not blooming, the best advice might just be to remove the rose and plant something else. Some causes are hopeless.