Osmocote for pond plants

[killi69]

Hi there,

I am looking into using Osmocote slow release fertiliser tabs for existing pond plants in baskets. These would include submerged aquatic plants like giant Vallis as well as a range of marginal plants. I know the cheapest way would be to add loose fertiliser like Gro More or Vitax Q4 to the planting mix but because I already have a large number of existing baskets, I am exploring the best tabs to buy, as making DIY tabs will be too time consuming.

The standard Osmocote slow release tabs (NPK 14 9 11) come in pouches of 25 and cost around £4-5 each, so work out at roughly 20p for a 5g tab.

Buying a similar product in bulk, 1000 x 7.5gr Osmocote Exact Tablets 5 -6 Months Slow Release Fertiliser (NPK 14 8 11) cost £110, so roughly 11p for a 7.5g tab.

I could also buy a product called Osmocote Exact High K (NPK 10-8-17), which for some reason is much cheaper, at £40 for 1000 x 7.5g tabs, so roughly 4p for a 7.5g tab. Would this be OK, or is the NPK not so great?

Many thanks in advance for your thoughts,
Andre

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[killi69]

And a second question, for a pond basket measuring 24x24x14cm (around 8L), how many tabs should I insert?

 

[ceg4048]

Hi,
Osmocote will be fine if used under the substrate or deep in the basket if the plants are potted. It uses ammonium nitrate so if there are fish in the pond you should be careful with it's use.

Cheers,

 

[killi69]

Thanks Ceg. What about the difference between the 2 Osmocote products? Do you think I can go for the cheaper one and not worry about the NPK balance?

1000 x 7.5gr Osmocote Exact Tablets 5 -6 Months Slow Release Fertiliser (NPK 14 8 11) cost £110, so roughly 11p for a 7.5g tab.

I could also buy a product called Osmocote Exact High K (NPK 10-8-17), which for some reason is much cheaper, at £40 for 1000 x 7.5g tabs, so roughly 4p for a 7.5g tab. Would this be OK, or is the NPK not so great?

 

[zozo]

Aquatic Plant Fertiliser (Osmocote) - accessories

May be used per 14L planting container, and should be inserted one finger-length into the soil around the rhizomes. The tablet form ensures that the nutrients stay in the mud and do not diffuse into the water, where they can encourage algae proliferation.

latour-marliac.com

Three tablets may be used per 14L planting container, and they should be inserted one finger-length into the soil around the rhizomes.
Formula NPK favors flowering: 10-11-18+2MgO+TE.
The tablet form ensures that the nutrients stay in the mud and do not diffuse into the water, where they can encourage algae proliferation.

Their product comes closest to your second option... Following their advice, it's 1 tab p/5L. If I'm not mistaken it's the higher P content favoring flowering plants during flowering periods.

I have a hunch that the above shop selected this specific tab to grow Water Lilies. I've personally used Osmocote tabs NPK 15-10-12 + 2MgO + Micronutrients on pond plants... Never experienced any ill effect on the fish. But I experienced that it highly depends on the sp. of plants you are growing. With this Tab I used, my Potentilla palustris still showed insufficiencies. It's an extremely hungry fast-growing and early flowering plant. But take for example the Iris pseudacorus, even faster-growing and earlier flowering and it keeps coming back every year more abundant and I never fertilized it at all.

It's kinda trial and error to find out if you found the one size fits all tab. 🙂

Could be other factors that play a role in plants' favor... In my case I have a rather high pH 8.5 i'm kinda stuck with. Some plants simply don't seem to like it and stay behind in development. But this is just a guess... But I did read that at higher pH values some elements are more difficultly available. Then a plant that has more demand for this specific element might suffer no matter how much fertilizer you add. There is some Potamogeton sp. that is used as a natural pH indicator for ponds. If pH goes about 8 this plant suffers calcium precipitation on its leaves. And absolutely not favoring its growth.

 

[killi69]

Thank you Marcel, that is very useful information. I will go with the second option as those tabs are so much cheaper, even though they seem formulated esp more for flowering plants. My water lilies will appreciate them the most then. I really need to get some Potentilla palustris... I have quite a bit of hair algae at the moment, which I why I wanted to give the plants some feed.

 

[ceg4048]

Thanks Ceg. What about the difference between the 2 Osmocote products? Do you think I can go for the cheaper one and not worry about the NPK balance?

Hi Killli,
Yes, get whatever is cheapest. Aquatic plants do not really care about balance.

Cheers,

 

[killi69]

Thank you Ceg. That's great to know!