Ask the head gardener: Why are my rose petals turning brown and falling off?

Telegraph

4 days ago

Dear Tom,
We have an annual problem with our roses. They bloom wonderfully, with large flowers, but the petals drop very quickly (after three or four days) and sometimes go brown around the edges. Otherwise they look healthy. No rust, black spot or aphids. Any ideas for how we can solve this problem?
– Brian
Dear Liz,
A healthy rose in full fettle can be hard to beat, but when things don't go to plan, it can be incredibly frustrating and pretty miserable-looking.
I recently judged the roses at the Hampton Court Palace Garden Festival, and I have to say that the hot, dry conditions were far from favourable for the nation's favourite flower. Despite the incredible talents of the rose growers at the show, namely David Austin, Peter Beale and Harkness, the blooms were showing signs of stress on day one.
When it comes to your roses, there are a number of potential issues which I'll highlight, requiring further investigation from you to decipher which is causing the petal drop. The heat and dry conditions would accelerate the deterioration of rose flowers. It is tricky to overcome the heat issue, but first, check if there is any moisture within the soil around the base of the shrub. Dig down by 10cm, and if no moisture is present, then regular watering through dry spells will help.
Next year, apply a thick layer of mulch in the spring. The use of grey water is perfectly adequate for roses; washing-up water with the food particles removed or bath water without salts will help to sustain your plants.
Feeding your roses every month through the growing season with a granular rose fertiliser will help to keep the shrubs in good health and extend flowering. Once you've applied the feed, water in well.
There are several diseases which will affect the health of your roses, as well as pests such as thrips, which are hard to spot with the naked eye but cause damage to most flowering plants. The best way to combat either pests or diseases with your roses is through good husbandry and hygiene. Clear away any dead flowers or foliage and pop into the bin, rather than the compost heap. Remove any crowded areas of stems to maximise air circulation and don't overplant the areas around the shrubs, which will restrict air movement and increase the potential for pest and disease and their spread.
Growing healthy roses through challenging conditions is becoming more of an issue. I remember at the start of my career that monoculture rose beds were commonplace, but the spraying regime to keep them healthy was also common practice. As we garden through more erratic conditions and move away from maintaining plants with chemical intervention, there needs to be a new approach.
Using roses in a mixed planting will avoid the group of bushes becoming a magnet for specific pests and diseases. In mixed plantings, allow a reasonable amount of light and air movement around your roses to minimise issues. Some old-fashioned roses such as hybrid teas and floribundas can be less suited to drier conditions and become more prone to diseases such as black spot.
Here are a few roses that have stronger disease resistance and are more tolerant of less ideal conditions, if your roses do not improve: