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Pumice and Coco Coir, Discoloured Pumice, Haworthia Watering Questions

Louise (UK)
5 years ago

I'd really appreciate some advice from more experienced growers, as I'm feeling stuck and overwhelmed by the amount of conflicting information online.

I recently switched my collection of Haworthias to a 70% pumice (3mm approximate partial size) and 30% coconut coir mix, top dressed with a thin layer of pumice.

After the first watering, over the first 1-3 days I noticed that parts of the top layer of pumice turned a rusty orange colour. Initially I thought this was caused by 'hard' water and so switched to a high quality distilled water, but the same thing occurred, orange pumice.

The amount of orange has varied from plant to plant, but the result is similar when using tap, bottled, and distilled water; also when watering from the top, and when watering from the bottom (the plants do not sit in wet water trays and the excess water is wicked with a paper towel).

Has anyone encountered this problem before with pumice and coir? Could it be the coir (I used Canna Coco Professional Plus) reacting with the pumice, or just the pumice itself?

My biggest concern is if this reaction, and the mix, is going to cause problems for my plants, particularly over time. I'd also like to avoid water marks from mineral build up on the plants. Am I needlessly worrying or is it a cause for concern?

My other concern is the current drying time of the mix.

The room in which I grow my Haworthias is ventilated (an air purifier, with a fan, circulating the air 24 hours a day) and at a day temperature of approximately 20°C (68°F), a few degrees less during the night, with 50% humidity. They are set back from a south facing window (but daylight hours are low at this time of year).

I weighed the pots before watering, and it's currently taking 2 1/2 weeks for the mix to return to its start weight (I've only watered once).

My plants are still in active growth (in bloom, noticeable growth), hence why I'm watering in Winter (I'm located in the UK). As they are grown indoors in a room that is used often by myself, I can't put them into a winter rest by dropping the temperature.

Is the time it's taking for the mix to dry out a cause for concern? What is the ideal time for Haworthias that the mix should remain damp?

Given the conditions I expected it to dry much faster. Again, am I worrying unnecessarily or is it a cause for concern? How long is the ideal time for the mix to dry back to its start weight?

I can take a photo to upload later of the discoloured pumice (if requested).

I'd greatly appreciate any input regarding these issues. I've read an abundance of information online but can't find the answers to these questions.

Thank you in advance for any help!

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