Algal Growth on LECA

[dnatural1]

Hi All,
After deliberating for over 1 year and doing a lot of reading (including that on Ray Barkalow's site) I started a semi-hydroponics trial. The purpose of this trial is find out what works for me (not to assess the method). So for I've had very encouraging results.

My setup is as shown in one of the attached pics. Basically I sit the pots (mainly of Phalaenopsis orchids at this stage but I also started trialling Cattleyas) in a tray of nutrient solution - each pot sitting at a depth of approx 2cm in the solution. The purpose of this setup is to allow me to withdraw the pots completely out of the nutrient solution when the weather gets cooler (as I'll probably do). Most of the pots have wicks which I used when the pots were sitting over the solution (on a mesh sitting over the tray). I had problems using this method as the wicks wern't drawing in enough water. The nutrient solution is 5mL/L of Orchid Focus from Growth Technology. I change the nutrient solution about once every 2 weeks.

The problem is that I'm seeing algal growth on the top layer of the LECA (I'm using Canna LECA). I have two questions:
- Is this algal growth harmful?
- How can I remove it if it is harmful? I'm thinking of using Banzalkonium Chloride (used to treat swimming pools for Algae). Others have used this product for orchids with no reported issues.

Ideas/suggestions welcome.

[Waterdog111]

I think Ray might be the best to ask.

[Ray]

Any time there is water+light+nutrients, there will be algae growth.

The algae is of no consequence unless it gets so thick that it starts clogging the air flow, but honestly, a top layer often fosters the growth of moss, which the plants seem to like, as do many growers.

I recommend against chemical treatment to eradicate it, as toy just end up with a lot of dead vegetable matter in the pot. If it is too much, simply “brush” the top layer of LECA out of the pot and replace it with new pellets.

You’re seeing it on the LECA because it’s wicking water to the top better than most other potting media do, but heavy algae growth is often the indicator of overfeeding. What is the %N in that fertilizer?

[estación seca]

Sharing water like that means diseases would spread quickly from pot to pot if they appeared.

[dnatural1]

Hi Ray, Estacion,

The N:P:K:Ca:Mg (%W/V) of the fertilizer is
2.4 : 0.5 : 2.0 : 2.0 : 0.5

There is a formulation from that brand, that is also orchid specific, but targets flowering - the N:P:K:Ca:Mg is different. I'm not using it right now but will later on.
Hope that the algal\moss growth doesn't get to the point of blocking airflow through the LECA - if it doesn't I don't mind having it there.

Good point Estacion about disease spread. The setup I have is convenient for me as it allows me to easily control the watering\feeding in the various seasons - I can just draw the plants out of the water during the cooler months as I need to do. If disease spread becomes and issue I'll have to deal with it then.

Thanks for your replies

[Ray]

I think you’re overfeeding.

For continuous exposure to fertilizer solution, as is the case in S/H culture, I recommend no more than 25 ppm N. At 5ml/L, that fertilizer is providing more along the line of 130 ppm N.

And there is no such thing as a fertilizer that promotes blooming.

[dnatural1]

",,, providing more along the line of 130 ppm N ,,,", Worked it out and it's 120 ppm of N. Close enough.

Actually it gets worse than 130 ppm N. As I'm using an 'open-top' system there is a lot of evaporation. If we get some hot days here, as we do,then the combination of the hot/dry air and the fans blowing through the greenhouse can drop the water level in the tray to half in a week. This would almost double the nutrient concentration. I've contacted Growth Technology about this - we'll see what they have to say.

(.. And there is no such thing as a fertilizer that promotes blooming. ...) - Interesting!

[Ray]

When I created the semi-hydro concept for orchids, some 25-30 years ago, I used (and still do) individual pots with sidewall drainage only (2 x 6mm holes) about 3 cm up from the bottom. That created the reservoir and did not require sharing the bath, which both limited cross-contamination issues and reduced the evaporation surface compared to a shared bath.

I watered as often as I wanted with 25 ppm N solutions. That was typically once a week in winter, 3-4 times a week in summer, and I once did an experiment to prove one could not "overwater", during which I watered daily for 6 months with zero losses.

The entire concept behind feeding is "provide enough, avoiding deficiencies and excesses", and it is one of the least important aspects of orchid culture.

I think THIS ARTICLE explains the "bloom booster" mytrh pretty well.