How to stop Rosemary dying off again?

[John57]

I’ve had this issue before, posted here but can’t find that post. 
The rosemary plant is dying off again. The same place, so presumably the same plant. See my photos below. Conjecture last round included cramping and lack of circulation but seems pretty unlikely as you see the last round of trimming the dead branches created plenty of space between the branches.

So it must be something attacking the plant, either the root system or the branches.

But look at the other plants next the dying plant. No issues so far. But is the bug in the soil that will simply crawl to the next plant?

I’ve similar challenges with lavender next to this plant and lost two lovely lavender plants too. Dang these plants are favorites with the bees. I want to restore this ecosystem.

When I removed the dead lavender plants they were simply dry root balls with no obvious issues, beyond being dead.

 

[MitchellMc · Accepted solution]

The problem could be related to soil drainage @John57, as both rosemary and lavender thrive in well-drained soil, and excess moisture can lead to root rot. If this area also has a clay base, then the roots are likely to be sitting in a bowl of water. Often, plants will grow quite well in the top layer of soil, which remains relatively dry. When they get large enough that their roots penetrate down to the clay layer, you'll see their health decline.

Additionally, pests such as aphids, spider mites, and scale insects could be causing harm, so inspect both the soil and the plants for any signs of these pests. Fungal diseases like powdery mildew or rust could also be a factor, especially if you notice unusual spots, moulds, or discolouration on the foliage and stems. Improving air circulation and using fungicides may help. 

Another possibility is a nutrient deficiency, so ensure your plants receive appropriate nutrients and consider using a balanced, slow-release fertiliser. 

Since the problem has occurred multiple times in the same location, soil-borne diseases might be a concern. You could try planting a different type of plant in the area or amend the soil with compost to improve its health. Lastly, inspect the roots of affected plants for any signs of rot or damage, as healthy roots should be firm and white. 

Please let me know if you have any questions.

Mitchell