Light Sensitivity in Plants

As I noted in my 1/12/17 post, some plants are tender from start to finish and cannot tolerate direct light for long periods of time or at all. At first I thought the sun scald could be mitigated with gradual introduction to the sun until the plant in question hardened off but that was not the case. As it turns out, there is no cure for sunburned plants only preventative measures. The least sun tolerant plants tend to be tropical houseplants such as Peace Lilies, Dieffenbachia, Parlor Palm, and Pothos; to name a few. Overall, if you normally see them in an office or a home, don’t put them outdoors unless they are placed in the shade.

 Pale Fruits

But what about the edibles that are grown outdoors? Those need the full sun in order to generate their own food and nutrients we need from them…right? Not necessarily. In my experience I have found that pale fruits and vegetables cannot tolerate full sun all day or part day sun. Light colored tomatoes, for instance, will burn and die at the nursery stage in all day sun. This happened when I directly sowed into the ground or started indoors and later hardened them. I found this to be the case for such varieties as Yellow Brandywine, Yellow Jubilee, Italian Ice, White Wax, and White Oxen Heart. The lighter they get from yellow to white, the easier they are to die in the sun. I find that I have to plant these pale yellow and white types of tomatoes in partially shaded areas or among other bushy sun tolerant plants or under a tree. However, they do their best in partially shaded areas. On the other hand, orange and pink tomatoes need more light than yellow and white ones but not too much more in order to avoid the scalding issue…at least in my garden. I have also learned that tomatoes such as strawberry orange and yellow pear don’t fruit well in partial shade but they do well in part day sun but scorch in all day sun.

Pale Veggies

Pale green vegetables can be just as tricky too. I noticed the scalding issue among my Buttercrunch and Frise. These pale green lettuce varieties also tend to wilt and die off or bolt quickly. Even the Romaine lettuce burns and bolts in the heat. The best results I have gotten from these green is by growing them in large tubs that I place in partially shaded areas or smaller containers that I can move about. I also add water absorbing crystals to the potting mix.  When I do this, they do not dry out or bolt at all and I get plenty of cuttings from them. When planted in the ground, I place them in between tomatoes and pepper plants to shade them. This is particularly beneficial for Arugula, a non pale lettuce, which I have had grow upwards of 4 feet tall with incredibly fat leaves. As such, my advice is to grow light colored fruits and vegetables in areas of partial shade or areas that do not get full sun for more than 1/4 of the day.  I should note that the latter sun issue did not occur among any of my light colored peppers. I have noted in the case of the peppers; they prefer the direct sun light and are better suited for the heat. This is especially true of the hot varieties.


Darker Vegetation

On the other hand, dark colored fruits and vegetables, in my experience, love the full sun. Still, some dark green plants like basil, spinach and pak choi have been known to scald and bolt in the heat in my garden, so I tend to plant those in pots in partially shaded areas or in the ground among taller vegetation. Still, I have observed that dark leafy greens such as kale and collards stand strong and tall in the heat but prefer sections of the yard that receive less than a  quarter of daily sun exposure. My red, purple, blue and pink tomatoes seem to be okay with all day sun. The same is also true for my peppers regardless of color and spiciness. The latter applies to my berries as well. In fact, for my blue and purple tomatoes and berries, the added sun light makes them darker in color. The only annoying thing is that these particular plants grow bigger outside of the constraints of pots so I have to choose wisely when considering where I plant these items and when.

My Investigation

When I looked into the matter, I found that scalding results from lack of water at the plant root, high heat, high winds that evaporate water from leaves and soil, and from planting in sandy soil. However, I watered religiously and have high fences and trees as wind breakers. In addition, at the time, my soil was healthy. However, I was not supplementing my soil and where I live has very sandy soil that drains quickly. Also, the area of the yard where I originally planted these tomatoes receives direct sun light all day, which is reflected back by the concrete driveway. As such, every gardener needs to not only pay attention to the sun and soil requirements noted on the seed packets but we must keep in mind which area of our planting space meets those criteria. You also have to consider factors that no planting book I have ever read seems to mention such as the driveway reflecting the sunlight and heat back. It makes perfect sense when you think about it. People often used those curved mirrors when tanning so it makes sense that can happen to plants as well.  As such, if our garden spaces are not up to snuff, we have to make modifications in our planting space whether that is soil supplementation or planting vegetation to act as shade or select sun and drought tolerant vegetation to plant.  The latter is tough when the things you love to eat and thus grow are somewhat light sensitive and not drought hardy. This is why, I believe, container gardening is becoming more and more popular among backyard gardeners.

A Note on Full Sun, Part Sun and Partial Shade

Surprisingly there is a big difference when it comes to the sunlight criteria. Full sun all day long will make most all plants burn depending on the temperature, humidity and soil conditions. I also think that where you are located makes a big difference as it impacts the angle and strength of the sun’s rays. This tends to occur in summer where we experience the longest days, which translate to the most amount of sunlight for the year where the hottest parts of day fall within late morning and early afternoon. In some areas this can mean 12 hours of sun. Part day sun, on the other hand, means full sun but for only part of the day i.e. four to six hours instead of 12 hours. The latter is different from partial shade where the vegetation is placed in an area where the sun shines all day long but the plant is shaded; usually by other vegetation. For the time the sun shines in this partially shaded area, the light sensitive plant receives muted light.

If you are a gardener and have noted these phenomena in your garden, share your experience and whatever strategy you used to compensate for poor results. Post your pictures on my Facebook page. Feel free to share your own gardening tips and advice here on my blog or my Facebook page. Don’t forget to like, thumbs up and share.

Happy Gardening!


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