Cilantro (or coriander) is a tasty herb that is healthy – it has manganese, magnesium, and vitamins A, C, and K.
It’s also thought to help reduce high blood pressure. The annual is fairly easy to grow, although a little fussy.
It can change colors for reasons that are almost inexplicable.
For example, why do the stems go purple?
Cilantro stems turn purple because the plant is getting ready to bolt. It bolts when the plant is getting ready to produce seeds, first creating flowers. After it’s seeded, it’s done. Cilantro will bolt prematurely when stressed from heat, or unfavorable conditions of its soil or water.
Cilantro does take a couple of weeks to germinate, but it is pretty easy to grow. But once it has a few leaves, it becomes a little Goldilocks.
It wants to be sunny and warm but not hot or cold. It wants lots of root space, damp soil but not soggy, and there is a bit of room between moist and dry.
If any of this is off, it believes the plant apocalypse is imminent and bolts.
Reasons Why Cilantro Stems Turning Purple
Eventually, cilantro reaches the end of its life cycle – it’s an annual after all.
But sometimes bolting happens well before that point, and purple stems on cilantro are one of the tell-tale signs of this.
Here are some common reasons for stems turning purple, and possibly leaves turning purple, on cilantro.
1. Compacted Soil Bolts Cilantro.
Soil compacted around cilantro is not a good thing, but it’s usually an unavoidable part of growing the crop. When soil becomes compacted, usually from watering, especially container grown plants, it struggles – after all, it is literally suffocating.
It usually starts with a few of its leaves changing color, before the stems show any sign of change.
So, if you notice a few leaves changing color, or you physically see that your soil is becoming compacted, try to loosen the top layer of the soil gently.
If you can avoid disturbing the roots, you can use a finger or chopstick to fluff up the top half an inch of soil for better drainage, water, and oxygen exchange at its roots.
2. Hot Sun Can Make Cilantro Bolt.
Cilantro is not fond of constant shade, but it loves the sun unless it is hot.
Cilantro will live happily in up to 85F (29C), but it will bolt if that 85F is directly on it.
Most people in warmer climates grow cilantro in spring or autumn, avoiding frost, to prevent bolting due to heat. If using grow lights, use a lower setting and maintain a distance of 4 inches.
Cilantro prefers to be in the ground, but if put into a large pot, you can move it to a shady spot on hot days.
You could also make some temporary cover (with shade cloth) to put over them on very hot days.
If you are fortunate enough to find a spot that gets morning and late afternoon sun but is shaded from hottest points, even better.
Did You Know? Early signs of too much hot sun on the cilantro are crispy leaves, or the leaves will turn from bright green to a lighter green.
3. The Wrong Soil pH Can Make Cilantro Bolt.
Cilantro prefers slightly acidic soil.
Its happy place is a soil pH of 6.5-6.8. It is also quite tolerant of soil out of this range, as long as the soil drains well and has nutrients.
But if the pH of the soil is too volatile like your wacky cousin, it will complain. Generally the leaves will begin to change color before it starts turning purple.
If you suspect it is the pH of your soil, you can buy a DIY pH kit and check:
If you find that it doesn’t have enough acid (it’s below 6) you can fix it by adding a small amount of limestone to the soil. If it has too much alkaline (it’s above 7) you can amend it with citric acid.
Just a reminder – mix citric acid with some water and do not pour it onto soil directly.
4. Overwatering Can Make Cilantro Bolt.
Cilantro does not like to live in soggy soil or to be overwatered.
Over saturated soil makes it hard for the herb to get enough oxygen so the leaves become wilted and discolored, or the growth becomes stunted.
If you realize your cilantro is too wet, try not to repot it while it is like that, as that will also irritate the plant, but if you must. do so gently.
Instead, use your best judgment, and try to dry the plant out until the soil is just moist. Loosening the soil always helps speed things along; if a storm moved through and drenched your containers, consider moving them indoors or to a sheltered spot.
5. Underwatering Can Make Cilantro Bolt.
Cilantro also has a pretty short temper when it dries out too.
It will yellow leaves, and it will bolt, often with the telltale purple stem.
You may have to water it a couple of times on a very hot day.
If you move it to a shady area or provide it a shade tent, it will help it from drying out quickly.
Can You Stop Cilantro From Bolting?
Unfortunately, once you hit the flowering stage, you can’t stop cilantro from bolting.
However, if you cut off purple stems and discolored leaves you can delay the full feathery leaves and white flower stage a little.
Also, the seeds, once they turn brown and are ready for harvest, are a great spice.
They can be ground up and used in lots of things, including curries.
What Are Some Varieties of Cilantro That Are Slow to Bolt?
There are many varietals of cilantro.
Some do taste a little different. Hey, it could be part of the fun!
Varietals of cilantro with more familiar taste that are slower to bolt are:
- Leisure
- Long Standing
- Jantar
Other options are Vietnamese cilantro and Culantro (from Egypt). The leaves look very different from the common varieties in the United States.
Instead of looking flat-leaf parsley, Vietnamese cilantro has long smooth leaves. Culantro enjoys shade and is sometimes sold as Spiny Coriander, because of its long spiny leaves.
Conclusion
Purple stems or discolored leave on cilantro tell you the plant is stressed and getting ready to bolt.
To minimize the bolting, try to keep it in its ideal (warm but not hot), with moist soil, not waterlogged (it doesn’t want to be sitting in a puddle).
Just remember, cilantro likes plenty of room for its roots and fluffy top soil.