AirWreck wrote: ↑Mon Jun 03, 2024 2:20 pmI need to remind myself which one it is that is desired- nitrate or nitrite?
Both are desired, although this requires an explanation as to why:
![Molybdenum.jpg](./download/file.php?id=99289&sid=f6b1df2c232a3f8cc07d4ac231208404)
- Molybdenum.jpg (87.47 KiB) Viewed 223 times
Poinsettias are succulents, so it stands to reason that all cacti and succulents are particularly vulnerable to Mo deficiency. Can they get Mo from the soil in a soil-based mix? Let's find out From Gardening Know How (
https://www.gardeningknowhow.com/garden ... bdenum.htm):
- "Molybdenum is a trace mineral important for plants and animals. It is found in soils that are alkaline with high pH levels. Acidic soils are deficient in molybdenum but improve with liming. As a trace element, molybdenum for plant growth is a moderately important catalyst for two very important enzyme activities. Plants can tolerate very high levels of molybdenum but do poorly with little to none of the element."
- "Sandy soils and acidic soils contain less available molybdenum for plant growth. The element is crucial to the functions of nitrogenase and nitrate reductase, two enzymes important for nitrogen-fixing and nitrogen reduction."
Plants growing in the open ground with the right soils have access to an unlimited supply of Mo from the soil, but plants growing in pots don't. This brings up another quote from Gardening Know How:
- "There are also many fertilizer formulations with molybdenum added, which will work well to increase the availability of the element in most plants."
Well, yes and no -- the fertilizers I've seen here in the US come up way short on Mo (if they even have it). Mike recommends 0.05 ppm per feeding (consistent with hydroponic applications), but the General Hydroponics 5-0-1 I use in my fertilizer regimen contains only 0.0008% Mo (0.005 ppm per feeding). Ferts
should contain 10 times the amount we see with the 5-0-1 -- 0.008%. I made up for the shortfall with a sodium molybdate stock solution, so my watering solution includes 0.053 ppm Mo per feeding. After 10 years of being Mo-deficient, the addition of Mo last year was a contributing factor in the substantial growing improvements I've seen with my cacti. Check your fert -- if it has the right amount of Mo, you don't have to worry about it. But if it comes up short (or it doesn't have any at all), let me know, and I'll give you the recipe for my sodium molybdate stock solution plus the proper dilution rate per gallon for your watering solution.
If you have nitrate or nitrate and nitrite in your pond water, the right amount of Mo in your watering solution will make the N available to your plants. The next thing we should look at -- the ppm number(s) you get from reading a Medlab Diagnostics test strip. If nitrate/nitrite N is 50-100 ppm, I'd recommend against adding more N with a fertilizer. I've seen growers blowing their cacti up like beach balls, and this is due entirely to excess N. (Well, that and watering too often -- definitely not a good combination for the plants.)
AirWreck wrote: ↑Mon Jun 03, 2024 2:20 pmI wish magnesium and calcium were on the strips and I don't know if Total Alkalinity and Total Water Hardness can suggest calcium/magnesium presence or concentrations.
You need hard water for that, and your pond water isn't hard.
AirWreck wrote: ↑Mon Jun 03, 2024 2:20 pmThat fact that there's algae growing in the pond indicates that there has to be some magnesium as magnesium is a component of chlorophyll.
Correct. Your pond's source is water percolating up through a dolomite (calcium magnesium carbonate) formation, and the water is already acidified for you. Since the Mg is available to the algae for chlorophyll production, it'll do the same for your plants. The only way to know the amounts of Ca and Mg in the pond water will be taking a sample to a test lab (hello, JR Peters!). Unfortunately there are no shortcuts on this one.