Dear MGs, could you please help me. I have started some marigold seedlings very early as part of my horticulture course assignment. They are very healthy looking, are growing under their very own grow light, and are even beginning to blossom. On the new shoots (but not the older leaves) are very regular dots. The dots are small, purple, evenly scattered on the leaf, and the edges of the leaves are a little purple as is the petiole. The dots look like bumps that are popping out of the leaf. Any help?
Thank you for our great question.
The baby plants look very healthy from the picture you provided. Your description of the dots as very regular gives a clue that this has something to do with the pores on the leaves (stoma). It could be normal for your cultivar . If it were a disease, a pest, or a fungus, the pattern would not be as regular nor on every leaf.
Two possible explanations are:
- Your plants may be over-transpiring due to excess moisture and excess heat. You could make sure the soil dries out between waterings just to see if it makes a difference, but if the plant is growing as expected, it should not be a concern.
- Your plants may have a nutrient deficiency. Here’s part of an answer to a question posed to Toronto Master Gardeners about tomato seedlings turning purple:
“Plants exhibit purpling of leaves & leaf veins when there is a shortage of Phosphorus (P) in the soil….The best way of giving your plants the phosphorus it needs is some Bone Meal, sprinkle on and then lightly work into the soil. Do this carefully as you don’t want to damage any plant roots that may be close to the soil surface. Another alternative is to use an all purpose fertilizer which would give it the other macronutrients (N & K) along with a variety of micronutrients.”
Below is a link to an article in gardeningknowhow on plant deficiencies in tomato and marigold seedlings by Susan Patterson, garden writer and Master Gardener:
Best wishes on your course!