EC/TDS meter use in fertilizing bare-root plants

15 years ago

How much fertilizer to use is an old subject that has been beaten to death many times. Use 1/2 strength, don't over fertilize etc. Many threads on the subject but none that I can find specifically relating to bare-root plants.

My collection is 95% mounted/bare-root. Hot weather is here and there will be more of it so we are back to daily watering. Once again I'm twisting my brain to come up with the right amount of fertilizer. I use Grow More 20/10/20 which is Urea free. The Urea is no problem in potted plants as the bacteria convert it to usable form, bare-root plants are not surrounded by bacteria covered media so I think Urea free is better. I also add Sea Weed Extract, a little vodka and occasional beer (Vit B complex, beer is cheaper than Super Thrive). I sometimes give them some Horse Tea which I make from aged Horse Manure and use Epsom salts once a month.

I use a EC/TDS meter to monitor all this and my question relates to this rather than to what I give or don't give the orchids. How much ppm increase is best on a monthly basis for bare-root plants? All the literature refers to the amount a POTTED orchid should receive. A potted orchid is surrounded by the wet bark/moss/rock and gets watered once a week. It also gets fertilized either once a week or every 2 weeks. For this application the total increase in PPM should be roughly 200, give or take dependent to whom you listen. If your tap water measures out at 300, which is what mine usually does, then add 100 ppm every two weeks or 50 every week to get the desired 200 increase. Lets ignore other factors like ph for the moment, I do use Humic acid occasionally and also flush everything with clean water often but lets not get into that and keep the focus on ppm.

I water my bare-root plants once a week and usually bump the ppm content by close to 100. In addition I water daily and add a little, no more than 10 to 20, on a daily or every 2 days basis. This comes to a whopping 700 to 900 monthly increase. My plants seem to like it and thrive, I see no burnt root tips nor black leaf tips, so no sign of over fertilizing. Of course when they get watered, the wet roots are dry in a couple of hours so they do not soak in the solution like potted plants.

Other than observing the plants and letting them tell you whats right for them, which will always remain the best way to solve any problem, does anyone know how much to bump the EC/PPM level per month specifically for bare-root plants in a hot, non humid environment where the roots dry out fast. My plants appear to be doing well but there is always the nagging question if they would do better if I followed the instructions on the package or followed the general rule to give half of that.

Nick

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Comments (5)

daveh_sf
15 years ago
I've wondered about this question too. With ordinary plants in potting soil, the risk of over-fertilizing is that as the water in the soil is taken up by the plant or evaporates, the concentration of fertilizer salts can increase greatly. At some point the osmotic pressure of the water and fertilizer surrounding the roots can interfere with water uptake by the roots and possibly damage the roots.

With mounted orchids though, I haven't seen any information on what happens physiologically when watering with fertilizer. It seems three things are going on: (1) the roots are absorbing water into the velamen, (2) the roots are absorbing fertilizer ions, and (3) water is evaporating into the surrounding air. I would assume that you would want all of the fertilizer to be absorbed before all of the water on the surface of the roots is gone. Otherwise there would be a thin, dry coating of all the residual fertilizer on the roots. So the question is how fast roots can absorb fertilizer - anyone know? It would seem that for that reason, it would be bad to use any fertilizer at all when the air is warm and dry, since the water on the roots would evaporate too fast.
richardol
15 years ago
Nick, if you are trying to be precise and you have a collection of more than one species, it is going to be hard. If your plants are growing with no burned tips and bloom well, you are ok.

I have lots of mounted plants. I put no fertilizer in the watering. The roots aren't open to absorb nutrients until they are wet and that takes a few seconds.

To fertilize, I mix a systematic bug killer and less than half strength fert in a pump sprayer and spray the roots directly with a quick "hello" and move on to the next plant. I don't claim that my way is "ideal", but I have too many different plants to mix different fertilizers.

If you enjoy the quest for the perfect mix, go for it. But if it is detracting from the enjoyment of the plants, consider how random the fertilizing in nature can be.
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Sheila
15 years ago
I'm just getting started growing mounties & bare roots in baskets. Richard, how often do you spray your roots with this mix?
richardol
15 years ago
Once a week for the fertilizer. When the air temperature is high and light levels bright, watering is daily. In the dark, cold of winter, about once or twice a week for watering and once a month for fert.
orchidnick
Original Author
15 years ago
No worry, I enjoy every minute of it.

I intentionally water with straight water every second or third watering so there will never be a build up of residual fertilizer.

So using the standard 1/2 strength once a week keeps your plants happy. I obviously use much more but most of it ends up on the ground. Unlike a pot which gets heavy from watering as the moisture is retained, the water runs of the bare roots and fertilizes the gravel. The same of course is true of your plants.

Which systemic bug killer do you use and to what degree do you have to protect yourself?

Nick

EC/TDS meter use in fertilizing bare-root plants

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EC/TDS meter use in fertilizing bare-root plants

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