Unsuitable location
A common reason for leaves turning yellow is the wrong location. delphinium loves full sun, but needs loose, humus and therefore nutrient-rich and moist soil. In particular, the perennial does not like a place that is too shady or too firm - perhaps very loamy - soil. In such a case transplanting helps respectively. mending the soil with plenty of compost.
Larkspur suffers from nutritional deficiencies
Furthermore, yellow leaves are very often a sign of nutrient deficiency, for example because you have the delphinium not sufficiently fertilized to have. If this is the case, provide the plant with readily available fertilizer, for example a liquid fertilizer. Compost and other organic fertilizers are not suitable in this case because they have to decompose first.
Tips & Tricks
However, a nutritional deficiency can also occur as a result of root rot due to waterlogging. Larkspur needs a lot of water, but does not tolerate wet "feet". In such a case, the plant can usually no longer be saved.
