Actually I see it in my chervil seedling too:

First time growing dil, fennel and chervil an i have disease already?

Quick q before I read up. Should I throw these out including the soil????

.... looks to me to be a combination of too much coir and over-watering. I'll explain why.

Too much coir:

Coir is chemically and physically different from peat, so it cannot be used effectively w/o adjusting your practices or putting work-arounds in place that allow for the differences. As an aside, even if you were growing in a mix of peat and perlite, there is a high likelihood you would be having the same issues, but back to coir for the moment.

Sphagnum peat and coir have nearly identical water retention curves. They both retain about 90-95% of their volume in water at saturation and release it over approximately the same curve until they both lock water up so tightly it's unavailable for plant uptake at about 30-33% saturation. Coir actually has less loft than sphagnum peat, and therefore, less aeration. Because of this propensity, coir should be used in mixes at lower %s than peat. Because of the tendency to compact, in the greenhouse industry coir is primarily used in containers as a small fraction of a medium's volume and in sub-irrigation (bottom-watering) situations. Also, many sources produce coir that is high in soluble salts (processed with sea-water), so this can also be an issue.

Using coir as the primary component of container media virtually eliminates lime or dolomitic lime as a possible Ca source because of coir's high pH (6+). Gypsum should be used as a Ca source, which eliminates coir's low S content. All coir products are very high in K, very low in Ca, and have a potentially high Mn content, which can interfere with the uptake of Fe. Several studies have also shown that the significant presence of phenolic allelochemicals (toxic to other plants) in fresh coir can be very problematic for a high % of plants, causing poor growth and reduced yields.

Over-watering:

Almost all, if not all, herbs demand sharp drainage. Because coir compacts readily when watered from the top, the compaction literally squeezes the air out of the soil by reducing larger air pores between soil particles to tiny pores, which then fill with water. My educated guess is that your soil supports in excess of 4" of perched water. Perched water is water that remains in the soil and refuses to leave the soil when acted upon by gravity alone. You'll find this all explained in detail at THIS THREAD.

Since you are growing in a tub/basin with a relatively short (in ht) soil column, AND your soil supports a considerable measure of excess water, it's hard to believe the entire or nearly the entire soil column would not be 100% saturated. This image:

shows how the depth of the soil column can affect how much soil is suitable for root colonization. Roots need oxygen as much as they need air because oxygen is required to burn the fuel (sugar) that produces the energy to drive root function.

A combination of organic fertilizers and soil inundation often causes a toxic reaction (ammonium toxicity) to the ammonium produced under those conditions, not to mention the fact that there is probably not a complete array of nutrients, essential for normal growth to occur. I use Foliage-Pro 9-3-6 on almost everything I grow in containers. It gives the grower complete (read that to be 'effective') control over a nutritional supplementation program from a single source.

I could help you deal with the excess water issue (the containers DO have drain holes, yes?), but in this case, I don't think it will solve all the issues in play.

Al

Is it phosphorus or potassium deficiency that causes leaves to turn a reddish purple?

They should return to their normal green next weekend after celebrating Pride month...

@tapla (mid-Michigan, USDA z5b-6a): thank you so much!!!!! Wont it help if I transplant into fresh good potting mix or soil (in ground)? Might not manage the transplant but chances are better for it than doing nothing right? Or is it that after having become this way the plants can never come back for some reason?? If I cut off the affected leaves to reduce stress?

The pots and cups have fantastic drainage holes. I am maniacal about drainage.

Before having done much further reading let me say this. I tend to agree with you that after being in a pot with coir and perlite for a long time I find plants become unhappy. It just has not gone this far bad before.

Can I recycle that coir and perlite though? Into garden soil or by little amounts into outdoor potting mix?

@carolb_w_fl_coastal_9b: I think its phosphorus.

For the fennel at least I’d get it into the ground outdoors. It’s a four or five foot perennial with a large tap root. It would never be happy in those little pots. Dill and chervil are better sown direct into the ground. Suboptimal starter conditions and transplanting leads to bolting.

Tapla, many thanks for the explanation about coir. I had a horrible experience with potting mix this spring where seedlings had been doing fine, but potted up into the coir-containing mix, they just sat and sulked, refusing to grow and turning yellow. I will be on the lookout for mixes containing coir in the future.

Linda

Not sure where your going to get psychedelic pinks, yellows, and bronze leaves from coir. Coir can cause deficiencies in magnesium, iron and calcium. For the first two, the symptom is chlorosis. Period. Pale yellow leaves. Calcium deficiency usually manifests itself as just misshapen leaves. I agree that coir is not a good primary potting medium, but what you're seeing strikes me as rather different from what coir does. Coir is indeed often associated with high salt content, but salt too doesn't lead to colorful leaves. It leads mostly to dead leaves.

Is it phosphorus or potassium deficiency that causes leaves to turn a reddish purple? The most common cause of purple leaves is a deficiency of phosphorus (P) because P is required to make ATP and ATP is needed to turn sugars to starch and to load sugar into phloem for transport. No P - no ATP - no move sugars/starches - anthocyanin (purple pigment) builds up - plant turns purple. The most frequent cause of a P deficiency is cold soils, which is why so many plants planted out too early turn purple. However, a P deficiency is not the only suspect cause of purple leaves. Nearly any environmental condition that puts the brakes on growth (and the accompanying use of sugars), but does not limit sugar production (photosynthesis) can cause anthocyanin buildup and purple leaves.

If only the outer edges of the leaves are purple, that coloration might be a K or Mg deficiency, but coir is so high in K it's a near . If the center of the leaves are also purple, it could be too much Ca in the soil or the result of too much water in the soil blocking uptake of P and Mg.

Keep in mind that cellular pH has a lot of influence on what pigments become expressive in both blooms and foliage. As we try to analyze this particular issue, it's also good to recognize we're seeing both chemical and physical factors in play. In all honesty, I think this issue goes beyond trying to pin the poor performance of the plants on individual nutrients.

Wont it help if I transplant into fresh good potting mix or soil (in ground)? Might not manage the transplant but chances are better for it than doing nothing right? Or is it that after having become this way the plants can never come back for some reason?? If I cut off the affected leaves to reduce stress? Transplanting into the ground or a more appropriate medium is certainly a possibility, and I agree it's better than surrendering and giving up, but saturated soil conditions can do permanent damage to root systems, cause synthesis of chemicals that persist in the plant and limit root function, and leave roots susceptible to fungal infections that might not be noticed until weeks after the transplant. The morphology of roots in inundated plants also changes. Where normal terrestrial roots are filed with a pithy material called aerenchyma, the roots of inundated roots are filled with aerenchyma. This comes about through dissolution of some of the normal tissue to form pathways by which oxygen absorbed into stem and leaf tissues can diffuse to roots. Unfortunately, terrestrial plants do not readily make the transition back and forth between the two types of tissue.

The affected leaves aren't a stressor, only a symptom of the stress currently limiting the plant. When the leaves become a net user of energy (as opposed to a net producer), the plant's chemical messengers plant will already have been informed plant central and the plant will be in the process of shedding the leaves. The first step in leaf shedding (abscission) is resorption, during which the plant will be absorbing those nutrients considered mobile in the plant and other bio compounds from the leaves. The only good reason to remove them is when they are infected with a pathogen or they are blocking light from reaching other healthy leaves.

..... after being in a pot with coir and perlite for a long time I find plants become unhappy. It just has not gone this far bad before. That has been my experience too. I have done some experimenting with coir and CHCs as substitutes for peat and pine bark, respectively, and found the results to be poor, even after leaching the coco products and using gypsum and Epsom salts as a source of Ca and Mg because coir's high pH disallows using lime as a source.

Can I recycle that coir and perlite though? Into garden soil or by little amounts into outdoor potting mix? Most greenhouse ops limit coir to less than 10% of the total volume of a substrate because coir compacts and reasons mention in my first post. They also tend to bottom water plants in media with coir to limit compaction. You would be best served to mix it into your gardens and beds where it won't be able to impose any physical limitations and the far superior buffering capacity of the mineral soil will, nullify any potentiality of chemical issues.

Al

Coir has plenty of plant-usable phosphorus. So a phosphorus deficiency seems unlikely. In fact, recommended fertilizers for use with coir specifically avoid lots of phosphorus, and potassium as well.