I can imagine that spraying basil leaves with alkaline water could be a harsh treatment. However, I do not think that the interface between the roots and your water is very alkaline. Your soil is likely to have extensive buffering factors such as the presence of salts from potassium, phosphorous, and nitrates. It would be interesting to to measure the pH of the liquid that drains at the bottom of the pot to see if the pH is closer to neutral.

Thanks, Chervil. I'm pretty new at this so I want to make sure I understand. You're suggesting that even though I may water with pH 9.1 water, what the plant actually drinks up through its roots ends up not being so alkaline? The salts you mention act as buffers to help bring the water down towards neutral?

If this helps in diagnosing this, I also am growing small arugula plants from seed, watering with the same water as with my herbs. Some of the leaves look fine, some look as gnarled, curled-up and deformed as the basil leaves, and one leaf was really really misshapen as this picture shows. I have a number of basil leaves that also look like this.

The garden consultant who looked at the plants says he is convinced that this eaten-up appearance of the leaves is NOT from insects doing any eating, but probably rather from the plants getting inadequate nutrition due to the extreme alkalinity of the water which makes it difficult for the plants to form uniformly healthy leaves.

Any thoughts?

Who was this 'garden consultant' and were they trying to sell you a product or service? I hope you didn't spend any money on them. I know nothing about soil/water pH, but I can assure you that your last picture shows physical damage by a creature of some kind. Nothing to do with nutrition. May be a snail or slug. Check under the pots. Also wait until after dark and check your plants. And look under the leaves for almost microscopic sap sucking pests such as spider mites.

Secondly, many basils have naturally puckered leaves and since you're quite likely to be chopping or tearing them anyway eventually it doesn't really matter that much.

Basil, thyme and oregano all grow in the wild in alkaline soils. Here wild oregano grows well on almost pure chalk. soils.

Good luck.

Thanks, Flora -- I really appreciate your thoughts here. Yeah, I just don't know what's going on. The leaves of the outdoors basil plant that I took these cuttings from were all were perfectly formed, not puckered or gnarled. It's only the plants grown from the stem cuttings that have leaves that way. And many of the leaves on these indoor plants are fine, but a good number of them look eaten and gnarled.

The puzzling thing is that there are NO insect eggs to be seen on the underside of these eaten-up-looking leaves, either the arugula or basil. Every time I see one of these leaves I check it, but there's nothing to be seen. Here's a photo of one of the eaten-up-looking basil leaves. It certainly does look like insect damage but I just don't see any evidence of insects on the leaf.

I know nothing about this, but I imagine it is possible that slugs or snails could have somehow made it into my house and up the stairs to the second floor, but...? I'll check under the pots tonight.

Thanks for the info that basil, thyme and oregano grow in the wild in alkaline soils. I hadn't been aware of that. So your guess is that pH 9.1 water should not pose a problem for growing the domesticated versions of these plants?

I'm as puzzled as ever, and learning a lot through the adventure.

Got any indoor cats? They can also cause "mysterious" damage to plants. ;)

FataMorgana

Hah! No cats (unless they sneak in at night... :-))

Rick, The pH of water can fluctuate over a broad range due to lack of buffering capacity since I am guessing that your water is pure and free of salts and minerals. Perhaps your water department source could confirm this. Your growing medium contains salts and minerals from fertilizer and soil components. I am explaining that the addition of water to your plant is creating a more buffered solution through the dissolving process of the salts and minerals present in the soil. I think it would be informative to measure the pH of the water draining from the pot.

Thanks, Chervil2 -- this is all new to me and I'd like to educate myself more. Can you suggest where I could read more about pH and its relation to indoor plants? I'm trying to grasp the concept of "buffering capacity" and how exactly it works. Salts and minerals provide a buffering which means that the pH value remains relatively stable? These minerals can come either directly in the water, or the soil, or the fertilizer? Why would pure water, without these minerals, fluctuate in its pH value?

Sorry for all the questions! Looks like I'd better read up on pH. I sure am learning a lot -- which is funny because all I originally intended was to grow a few herbs for dinner. Now here I am diving headlong into learning the nuances of water chemistry...

Most of my pH knowledge come from my working knowledge from employment in laboratories. In my present job, I have students start solutions with purified water with the addition of salts guided by pH meter use. The students and I always marvel at how well phosphates and nitrates buffer the pH of the solution.