Fertiliser Dosage

[From0to10in2weeks]

Hi,

I repotted my plants in July into a 2:1 mix of Seramis cactus substrate and a peat-free all purpose soil. So far, I haven’t added fertiliser during watering yet but I am considering doing it now once or twice before the wintering period. Just to strengthen them up a bit. I am aware that transitioning to a dormant state with less watering needs to start soon. Note, they are indoors.

I bought a 3:5:7 NPK fertiliser at a local cactus nursery. The recommended dose is 5 ml per 1 liter of water. Do you think this is okay? I kind of remember seeing some recommendation here or somewhere else to only use half of the typically recommended dosage…

Any other things to consider re fertiliser use?

Thanks. Best.

[x_101]

Yeah, usually people recommend quarter to half the strength for cacti, so 5ml to 2-4l of water should be enough.
Some even say cacti don't need any sort of fertilizer if your soil has the necessary nutrients in it. Others use only microelements fertilizer.
I started using some seaweed concentrate, but it is too early to say if there's any difference. It is really a waiting game with these plants.

[DaveW]

Seramis is an inert clay medium so you need to make sure the fertilisers contain trace elements or at least use some that add them occasionally (read the packaging to see). Some fertilisers intended for soil based potting mediums or the garden do not contain all these trace elements as they expect them to be available in the soil in the minute quantities needed. I believe Seramis used to do their own fertiliser containing trace elements, but how good it is for cacti I do not know.

https://www.succulent-plant.com/fertiliser.html

https://ph.farmforage.com/6226-ceramis- ... lants.html

The Bonsai people discovered some forms of clay cat litters were similar but cheaper than Seramis, therefore many of us copied them and used that as a potting soil ingredient. Unfortunately that Bonsai site is now closed, particularly as it used to list the granulated clay alternatives around the world. However in the UK we now have our Tesco low dust clay cat litter back again as well as Sophisticat, but other UK cat litters are unsuitable for our plants since they range from from clumping Fullers Earth types to shredded paper, so be sure you get the right one.

http://desertplantsofavalon.com/tag/cat ... or-cactus/

[teo]

There is also products for absorbing oil spills etc (Oil-dri) made by the same manufacturer (Damolin A/S, now Imerys). See: http://damolin.com/

[From0to10in2weeks]

Seramis is an inert clay medium so you need to make sure the fertilisers contain trace elements or at least use some that add them occasionally (read the packaging to see). Some fertilisers intended for soil based potting mediums do not contain all these trace elements as they expect them to be available in the soil in the minute quantities needed.

Hi Dave,

Thanks for the heads-up. The bottle lists as ingredients in addition to NPK the following elements: boron, copper, iron, manganese, molybdenum and zinc. Anything else needed?

But as indicated, I have mixed the Seramis with a peat-free general purpose soil (2:1 by volume). Best.

[DaveW]

Sounds as if it contains everything needed in micro nutrients.

[From0to10in2weeks]

Sounds as if it contains everything needed in micro nutrients.

Thanks for taking the time to confirm. Best.

[MikeInOz]

5 ml/Lt seems low to me but I would like to see the NPK on the bottle before commenting further.

[From0to10in2weeks]

5 ml/Lt seems low to me but I would like to see the NPK on the bottle before commenting further.

Hi Mike,

The composition is as follows per the label on the bottle:

3% total nitrogen: 0.75% nitrate, 0.75% ammonium, 1.5% carbamid (urea)
5% P2O5
7% K2O

Thanks. Best.

[DaveW]

15% total N-P-K, what's the other 85% in the bottle expensive water, surely not trace elements?

[From0to10in2weeks]

15% total N-P-K, what's the other 85% in the bottle expensive water, surely not trace elements?

Yep. It's the HP inkjet ink model.

Trace elements:
boron: 0.01%
copper: 0.002%
iron: 0.02%
manganese: 0.01%
molybdenum: 0.001%
zinc: 0.002%

[MikeInOz]

5 ml/Lt seems low to me but I would like to see the NPK on the bottle before commenting further.

Hi Mike,

The composition is as follows per the label on the bottle:

3% total nitrogen: 0.75% nitrate, 0.75% ammonium, 1.5% carbamid (urea)
5% P2O5
7% K2O

Thanks. Best.

That's quite weak. I would stick to the instructions of 5ml.

[From0to10in2weeks]

That's quite weak. I would stick to the instructions of 5ml.

Thanks for the followup. Best.