Lavender, Rosemary Cuttings Die-Back
Answered by: Conrad Richter and Inge Poot
Question from: Korean Herb Grower
Posted on: June 01, 2004

We are herb growers in Korea. We have propagated a lavender and a rosemary by taking cuttings from a mother-plant. Recently after taking cuttings and planting them, some baby plants are changing to yellow. They are losing their color and the other difference is that healthy lavenders absorb water well, but abnormal plantlets do so less well. We didn’t add any fertilizers. The weather is getting sticky and the temperature is around 27C. In my opinion, the reason seems to be a soil problem. We have used a soil including some vegetables and manures. I believe your answer would be very helpful.
 


A few possible reasons come to mind: one, the pH of the soil might be quite different from the one the cuttings were started in. Rosemary and lavender both like alkaline soil. Rosemary tolerates a pH of 4.5 to 8.7, but does best at 6.8 to 7.5. Lavender will tolerate a pH of 6.4 to 8.2 but do best at pH of 7.2. Adding lime to the watering water should help.

Another reason for the yellowing and tip die-back of the plants could be root burn. Perhaps the manure in the potting mix was too fresh and burned the roots. Repotting would be the only quick solution. Because of the mixing with sandy soil, the fresh manure bits would rot fairly quickly and the problem would solve itself in time.

Because the weather is now muggy, fungi and bacteria would love it and might be able to infect plants now. Try spraying a few plants with a fungicide to see if this helps. You can then make the choice of either spraying all of the plants or tossing out the affected ones and hoping the rest have not already caught the infection. A methyl alcohol plus water and powdered cinnamon spray or a powdered sulphur in water spray may act as a preventative. Even neem oil is anti-fungal and anti-bacterial. The last three suggestions are not harmful to humans -- as soon as the methyl alcohol evaporates!

Lastly, if the hot weather came on rather suddenly, the root-mass might not be adequate to cope with transpiration and the tips would die back to reduce the top to match the capacity of the roots. I would tip a sick looking plant out of its pot to check if the roots look healthy and thus are possibly just inadequate or if they look discoloured and sick and are therefore probably burned or suffering from the wrong pH. You should also check that the watering was adjusted when the weather turned hot and muggy, the plants may not need as much water as during cooler temperatures, if the humidity is high enough. Soggy soil kills the roots of these plants.

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