Tomato transplants experiencing problems
If your tomato leaves are developing irregular tan spots soon after planting, they could be getting too much sun.
June 3, 2011 - Author: Gretchen Voyle, Michigan State University Extension
Spring is that glorious time of garden planning and planting. As many people purchased tomato transplants from stores or raised their own indoors, they took them outside in preparation for planting. These plants were soon planted in gardens or in big pots on the patio. Within several days, the tomato leaves looked bad with irregularly shaped tan spots scattered all over the upper surfaces of the leaves. The tan spot met the green of the surrounding leaf with no discolored area in between.
The next day, more spots appeared or the spots grew larger. The spots rarely appeared on the edges or margins of the leaves. For gardeners, the concern is always new or weird diseases popping up, but those could be discounted because of the early season and young plants.
The “bad guy” was plain, old sunburn or leaf scorching. Plants grown in greenhouses or indoors only receive a small amount of the sun’s energy on their leaves. They grow big, beautiful, soft green leaves because there is not enough sun.
Essentially, they are producing “shade leaves” in response to the light they are receiving. These leaves are extremely efficient in capturing sunlight. When moved outside, the length and intensity of light dramatically increases. When those large shade leaves are exposed to this overdose of sun, they begin to burn. They cannot change. The leaves are not designed for this much sunlight.
In the experienced gardener world, those transplants would be moved outdoors under a shade tree. They are receiving more light there than in their previous home behind glass. Over a period of several days or a week, new leaves will be produced at the top of the plant. These new “sun leaves” are smaller and a darker green, sometimes edged with a bit of red. They are also less efficient in taking in sunlight because they now have more than enough. As new leaves are produced, the plants are moved to brighter light. This process is called “hardening off.” Once there are adequate sun leaves, they are now tough enough for the mega solar blast in the garden or on the deck.
Consider that these sun-loving garden stars originated in South America. Tomatoes are built for as much sun as they can possibly get in Michigan. They just have to get acclimated. It takes a great deal of energy to produce flowers and fruit and the sun is the primary energy source. Once the sun leaves are being produced and the plant is growing, tomato fruit is in the near future. Bring on that crispy bacon and mayonnaise.