The picture below is of clematis Bourbon. Some of its older leaves are turning purple and I don't understand the reason. It has been like this for couple of months, we have new growth which makes me think that it is not a desease but some sort of malnutrition. However, I am not sure what it needs as we are feeding it once a month with high potash feed. Could you please help me with identifying the root cause and what can we do?

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    Tomorite is the wrong formulation for this. You don't want high potash unless you are trying to produce clematis seeds. As @bamboo said you probably don't need anything at all if the plant is growing in the ground. I have clematis that have got up to the roof level and are now trying to bury the whole house, which have never had any fertilizer since they were planted 10 or 20 years ago. – alephzero Jun 15 '20 at 13:42
  • Thanks @alephzero I will stop feeding it with Tomorite then. – Rustam Aliyev Jun 15 '20 at 18:58

I would hazard an educated guess that you are over fertilizing the plant. Vitax Clematis feed is a slow release formulation, and lasts for 3 months. Feeding with Tomorite monthly as well is somewhat of an overkill, so I suggest you stop using the Tomorite and don't feed at all again this year, not even with the Vitax. Keep the plant well watered to try to dilute and clear away excess fertilizer. In the UK, plants in the ground really don't need much fertilizer and largely will grow perfectly well without any at all, though this is not the case in pots.

Clematis do best in neutral to slightly acidic soil in terms of soil ph; if you, or people in your area, are unable to grow blue hydrangeas, they're always pink, or cannot grow Pieris or Rhododendron in the ground, that would suggest the soil ph is alkaline - if it is severely so, clematis, whilst they might still grow, will not do very well. However, one of your other questions is in regard to Clematis Hagley Hybrid, and despite the presence of leaf miners, it otherwise appears to be healthy, so I'm not convinced the soil ph is too alkaline, assuming it is planted in the ground.

  • Hagley Hybrid is potted. But I have other ones that are in the ground, and they seem to be happy, e.g. Josephine, Carnaby, Crystal Fountain. We also have another clematis Rebecca which is planted next to Bourbon on the picture above which stopped growing. But once we fed it with general purpose fertilizer it started giving shoots. Maybe it is a coincidence? – Rustam Aliyev Jun 15 '20 at 18:55
  • Sorry, maybe what is a coincidence? – Bamboo Jun 15 '20 at 20:39
  • we were feeding Rebecca just like others with Vitax and Tomorite. We also changed our watering: we used to water once in 3 days and changed it to once in 2 days. We started seeing new growth several days ago which confirms your proposal. We will follow your advice and stop all the feeding and continue watering regularly. Thanks for your help. – Rustam Aliyev Jun 15 '20 at 22:12

What have you used for fertilizer? What formulation? This plant is suffering from lack of Phosphorus and Nitrogen, possible Potassium. What is the pH of your soil? One has to apply BALANCED fertilizer for all plants in the right amount and the right percentages. It is clear, your plant is lacking nitrogen and phosphorous. Where fertilizer is concerned I have to always add this next line: Less is BEST, More is DEATH, and None is DUMB.

  • Thanks @stormy . We used Vitax clematis fertilizer in April, then I feed with Tomorite liquid fertilizer once per month. I don't know what pH is my soil, don't know how to measure it even. – Rustam Aliyev Jun 14 '20 at 23:12
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    I think Bamboo is right; you are over-fertilizing! Less is Best, More is Death and none is dumb. Where fertilizer is concerned. That is a lot of fertilizer, too much fertilizer. – stormy Jun 16 '20 at 0:47

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