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Why Are Some Veggie Plants Turning Purple?!

As the temperatures drop in the garden, plants undergo fascinating adaptations to protect themselves from the cold. One such adaptation is the increased production of anthocyanin pigments, which not only provide vibrant colors to leaves and fruits but also play a crucial role in protecting plant tissue from the adverse effects of low temperatures. Last week's sudden dip in temperature has a few of our tomato and eggplant seedlings showing off their purple pigments!

What are Anthocyanins?

Anthocyanins are water-soluble pigments that belong to the flavonoid group. They are responsible for the red, purple, and blue colors seen in various plant parts, such as leaves, fruits, flowers, and stems. Apart from their aesthetic value, anthocyanins serve as a powerful defense mechanism for plants.

The Role of Anthocyanins in Cold Protection

When temperatures decrease, plants are at risk of damage due to factors like frost and chilling stress. Anthocyanins act as a natural "antifreeze" for plants by helping them tolerate cold conditions. These pigments absorb light in the visible and ultraviolet regions, protecting plant tissues from photoinhibition and oxidative stress caused by cold temperatures.

Increased Anthocyanin Production in Cool Temperatures

Cool temperatures trigger a cascade of biochemical reactions within plants that lead to the upregulation of genes responsible for anthocyanin biosynthesis. This results in an increased accumulation of anthocyanin pigments in plant tissues, providing enhanced protection against cold-induced damage.

Enhanced Plant Productivity

Interestingly, the boost in anthocyanin production not only helps plants survive the cold but also has positive effects on their overall productivity. Studies have shown that plants with

higher anthocyanin levels exhibit improved photosynthetic efficiency, enhanced antioxidant activity, and increased resistance to various environmental stresses.

Cold or Phosphorus Deficiency?

Purple discoloration can also indicate a lack of available phosphorus in the soil, so how can you tell if the purple is due to this or just the anthocyanin production due to cold?

Phosphorus deficiencies tend to look spotty and are accompanies with other signs of stress, e.g. dead or curling leaves, lack of flowering, etc.

The anthocyanin process we're talking about today is displayed in healthy plants.

Another clue for us was that only some individual plants in the rows are showing the increased anthocyanin production - a phosphorus deficiency in the soil would likely be affected all the plants in the area. So you, too, have been noticing this effect on a few taller plants or maybe some recent seedlings added to your garden during cool temps, don't worry! It's nothing to worry about and something kinda cool to observe.

If you are really concerned and cannot decide between cold temp effects and nutrient deficiencies, you can always lightly feed your plants with a general fertilizer (equal NPK levels, like a 10-10-10) or add a soil amendment such as worm castings. Be sure to side dress at this point - those tender seedling stems do not respond well to all those amendments packed right against plant tissue. Just add your amendments to the soil on the edge of rows and work it in a bit with your trowel or spade - avoiding your plants' root zones. The watering or rain will do the rest! Alternatively you could use a plant food meant to be applied in solution and spray it directly to the plant tissue - this can get you into other trouble however: you can cause sun scald if the moisture sits on the leaves during particualry strong sunny conditions; you can also cause damaging microbial growth if the moisture sits too long during cooler night temps. So we suggest sticking with soil amendments if you need to feed!

Happy gardening out there and may your plants bloom with joy this season!

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