If the compost feels dry when you push in your finger you need to water. If it feels moist, you don't need to water. Over watering will leach nutrients from your compost and also drown the roots so they no longer work properly.
It's also better to water deeply once a week than to dribble every day so definitely reduce watering frequency and make sure your pot is raised off the ground so it can drain well. Special pot feet or just plain bricks will do the job.
Monitor the compost for the need to water more frequently in hot, dry spells and don't rely on rainfall to do it for you as the plant's foliage will cast a rain shadow.
Vendée - 20kms from Atlantic coast.
"The price good men (and women) pay for indifference to public affairs is to be ruled by evil men (and women)."
She's hungry. Which could be because of under or overwatering or under or overfeeding. If she was only fed in spring, I would do liquid multi-purpose/balanced feed now.
Ok, I’m feeling very sheepish now. I visited Gertrude this evening and a lot of the leaves now look like the photos below. It is blackspot, isn’t it? … 😔
Your advice was still super helpful, about watering and feeding, thank you 😊
Now, is it too late for a sulphur treatment? Or a Neem oil solution? Or is a foliar seaweed feed better? I’m sure this has been discussed already a 1000 times, I will check the archives.
Looks to me more like malnourishment so stop watering for a few days so the compost can dry out a bit. Get the pot up on feet or bricks and give it a foliar feed of liquid seaweed either with a spray gun or a rose on your watering can.
Vendée - 20kms from Atlantic coast.
"The price good men (and women) pay for indifference to public affairs is to be ruled by evil men (and women)."
Ok, so I re-thought: with blackspot, the leaves only turn yellow when the desease has progressed a lot, black spots appear on green leaves, then later the leaves turn yellow. So blackspot is definitely not the cause of the yellowing leaves. So: less water, container on feet and foliar feed are the way to go.
Has anyone actually ever used anything to successfully prevent or halt blackspot ? My internet research does not give me clear answers. Are all commercial fungicides bad for wildlife?
Blackspot is worst with old roses and sick or weak roses. Yours is hungry so the laves lack chlorophyll which helps them feed the plant and are also thin so liable to damage form any floating spores of fungicide or viruses.
Please do stop thinking it over and over and get the pot drained and some nutrients into those leaves. A foliar feed is the fastest way and will not make your compost soggy.
Commercial fungicides are indiscriminate but there is one the French use and that can be made at home from horsetail/marestail weed. If you haven't got it in your garden find a friend or neighbour who does. This is from a post I made on one of the many horsetail threads:
Pull or hoe stems of horsetail and make a fungicide which is safe for plants and insects and can be used to treat or prevent mildew, black spot, peach leaf curl, seed dampening off etc:-
1kg horsetail stems 9 litres rainwater
Crush the stems and steep them in the water, covered, for 2 weeks or till it all turns black. Do not use a metal container. Strain the resulting goo and keep in sealed bottles. Dilute 1 part purin to 9 parts water and spray in spring or autumn when fungal problems are most prevalent.
Vendée - 20kms from Atlantic coast.
"The price good men (and women) pay for indifference to public affairs is to be ruled by evil men (and women)."
..that isn't black spot on your rose, it's cercospora leaf spot.. your rose is weakened, as edhelka has said, due to a lack of nutrients, so the rose has to shed some of its leaves as it cannot support them... in order to do this, roses reduce their immune system so they become diseased and drop off..
..on close up of your potting compost it would appear you've used multi purpose peat free, would that be right? ..this isn't adequate for roses if used on its own...
Your rose is starved because I believe it's totally pot bound... Gertrude Jekyll is a vigorous rose which forces the rootstock to quickly invade the soil in a pot and it isn't long before any nutrients in it get used up.. especially if you've used that type of multi purpose..
You can alleviate the leaf yellowing by scraping away some top soil and placing a 2 inch layer of John Innes no. 3 potting soil and work that in, then water... you will be surprised the difference this can make and will keep your rose going for the rest of the season..
Leaves with the spots can be snipped off.. the yellow ones will eventually drop in any case.. Using a fungicide spray at this stage is pointless.. the rose needs more and better compost..
I think the OP has already said the rose is in mainly JI No 3 with a bit of MPC as well.
My question is when was it last repotted?
Like everyone else I think your rose is hungry. That might be because it hasn't been repotted for a few years and the compost is exhausted and / or the plant is root bound and / or it's been overwatered and the nutrients have been washed out of the soil.
I would take @Marlorena 's advice to scrape away some soil and top dress with more JI No3. I would also give it a foliar feed when new growth appears and would make the new watering regime a full bucket or watering can added slowly every 3 or 4 days or whenever the soil is just starting to dry out.
If the rose hasn't been repotted for a couple of years I would also consider repotting it next winter when it's dormant. If you want to keep it in the same pot you can prune the roots (quite hard) to reduce the size of the root ball (cut back the larger roots and try to leave lots of the fibrous feeder roots). I would use a mix of 2:1 JI No3 and decent MPC.
Heaven is ... sitting in the garden with a G&T and a cat while watching the sun go down
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It's also better to water deeply once a week than to dribble every day so definitely reduce watering frequency and make sure your pot is raised off the ground so it can drain well. Special pot feet or just plain bricks will do the job.
Monitor the compost for the need to water more frequently in hot, dry spells and don't rely on rainfall to do it for you as the plant's foliage will cast a rain shadow.
Your advice was still super helpful, about watering and feeding, thank you 😊
Looks to me more like malnourishment so stop watering for a few days so the compost can dry out a bit. Get the pot up on feet or bricks and give it a foliar feed of liquid seaweed either with a spray gun or a rose on your watering can.
Garden and learn …
So: less water, container on feet and foliar feed are the way to go.
My internet research does not give me clear answers.
Are all commercial fungicides bad for wildlife?
Please do stop thinking it over and over and get the pot drained and some nutrients into those leaves. A foliar feed is the fastest way and will not make your compost soggy.
Commercial fungicides are indiscriminate but there is one the French use and that can be made at home from horsetail/marestail weed. If you haven't got it in your garden find a friend or neighbour who does. This is from a post I made on one of the many horsetail threads:
Pull or hoe stems of horsetail and make a fungicide which is safe for plants and insects and can be used to treat or prevent mildew, black spot, peach leaf curl, seed dampening off etc:-
1kg horsetail stems
9 litres rainwater
Crush the stems and steep them in the water, covered, for 2 weeks or till it all turns black. Do not use a metal container. Strain the resulting goo and keep in sealed bottles. Dilute 1 part purin to 9 parts water and spray in spring or autumn when fungal problems are most prevalent.
..on close up of your potting compost it would appear you've used multi purpose peat free, would that be right?
..this isn't adequate for roses if used on its own...
Your rose is starved because I believe it's totally pot bound... Gertrude Jekyll is a vigorous rose which forces the rootstock to quickly invade the soil in a pot and it isn't long before any nutrients in it get used up.. especially if you've used that type of multi purpose..
You can alleviate the leaf yellowing by scraping away some top soil and placing a 2 inch layer of John Innes no. 3 potting soil and work that in, then water... you will be surprised the difference this can make and will keep your rose going for the rest of the season..
Leaves with the spots can be snipped off.. the yellow ones will eventually drop in any case..
Using a fungicide spray at this stage is pointless.. the rose needs more and better compost..
My question is when was it last repotted?
Like everyone else I think your rose is hungry. That might be because it hasn't been repotted for a few years and the compost is exhausted and / or the plant is root bound and / or it's been overwatered and the nutrients have been washed out of the soil.
I would take @Marlorena 's advice to scrape away some soil and top dress with more JI No3. I would also give it a foliar feed when new growth appears and would make the new watering regime a full bucket or watering can added slowly every 3 or 4 days or whenever the soil is just starting to dry out.
If the rose hasn't been repotted for a couple of years I would also consider repotting it next winter when it's dormant. If you want to keep it in the same pot you can prune the roots (quite hard) to reduce the size of the root ball (cut back the larger roots and try to leave lots of the fibrous feeder roots). I would use a mix of 2:1 JI No3 and decent MPC.