AusBonsai

Hi Everyone, got a newbie question on fertilizers. Since springs on its way, i should begin fertilizing in the coming months. I'm wondering if Osmocote slow release pellets are enough for my trees or do i need to supplement with liquid ferts? Anyways, the specific fert i got is slow release 8:1:6.5 plus trace elements. So its got higher Potassium and lower Nitrogen- Is that fine for normal warmer month fertilizing or should i get something more balanced? And ive also heard that slow release ferts are bad in summer because they release too much and the trees aren't really growing much during the heat of summer...? Anyways, thanks!

I'm not exactly sure as I'm a newbie as well but I'd like some knowledge on fertilizing also. Does fertilizing differ from plant to plant or is it all the same?

hi Pezz95. im believe as a basic rule most species are fine with the same fert. its just that during different phases of growth, you may want to use a fert with different NPK ratios to promote flowering or root growth. just make sure you dont over fertilize and burn roots or for plants that are more sensitive.

Something like Osmocote is fine as a long term solution but you should be fertilising more during the growing season. Mix it up with organic and chemical, pellet and liquid. You should also use something like Seasol - which is regarded as a tonic and not a fertiliser. Remember too that growing on stock will need the heaviest fertilising - anything in a bonsai pot can be fed at lower doses. You can also do foliar feeding - something like THIS

I use about 5% rapid raiser by volume in my potting mix then use a weak tea of fruit and flower fert .plus a bit of charlie carp or seasol---no probs so far. I don't have any finnicky natives so It works for me - safer to use a weak mix more often

also heard that slow release ferts are bad in summer because they release too much and the trees aren't really growing much during the heat of summer...?

This was true of the early coatings but the companies have researched and improved their products to stop the hot weather dumping. Newer products are much more temp stable. I have never seen any problem.

Grant Bowie did some trials with osmocote and supplementary fertilisation. The ones he put extra liquid fert on grew much better than the ones that only had osmocote. I think it would depend a lot on how much you put in the pot but I also fertilise regularly during the growing season.
It will also depend on the release period of the osmocote. They make a range of different coatings for different uses. Some only last 3 months but they also have 6month, 12 month and 18 month release periods. If you put a 3 month osmocote in your bonsai all the nutrient will be gone by about November so additional fertiliser will definitely be needed.

The NPK you have listed looks like it is formulated for flowering or fruiting plants but other plants will not object if you give it to them. Plants cannot read labels. All they are interested in is nutrients wherever they can get them from. The osmocote you have will possibly give a little less growth because of lower N but any fertiliser is better than none.

'Balanced' does not mean equal NPK ratio. Balanced means there is some of each nutrient in the fertiliser. Plants do not require equal parts of N,P and K. Most require more N for growth.

Lots of members of the school use slow release ( Ozmocote ) and Ray nesci uses it too.
it supposedly last only 6-9 months anyway so to me you would have to add other fert anyway unless you do not fertilise over winter ( I do).

For trees that you repot in Spring or summer ( Tropicals and Natives), then they would be running out in autumn / winter and thus have no fertiliser for the spring growth.

For trees that are repotted less often ( Pines, Junipers etc) then they will get firt for the fist part of a year, then you will have to revert to manual fertilising anyway, so why not just do it manually with Liquids and pellets / cages from the start.

Ken

Another point to keep in mind when "designing" a fertiliser program for your Bonsai is the potting medium being used. With the open, well drained mix most of us now use, fertiliser leaching can be a real issue. If the ingredients of your mix have a low Cation exchange capability you will find you are adding fert' to your trees more often in order to keep the growth rate up. There has been a lot said about Zeolite and it's use in potting medium, but the one thing all seem to agree on is its high Cation Exchange capability. Adding Zeolite to a mix will ensure more fertiliser will be available to the plant. Another simple method of increasing the Cation Exchange capability of your mix is to add a good quantity of well rotted/composted cow manure to the mix. Composted Cow manure has almost a 100% Cation Exchange capability. Fresh cow manure should never be used in potting mix as it will simply turn to a sloppy mess and block the drainage of your pots totally. Once it starts to break down it will also get so hot as to burn the roots of your tree. Even the stuff you buy in bags is not composted enough and should be stored in open bags (or out in the open if possible) for several months. Fresh will take around 12 months to compost down, so neither is a short term solution.

Also, if the potting medium you are using contains a high level of Organic material, that has not completely finished composting, you will find a degree of feriliser drawdown occurring in your pots. This is because the Bacteria that performs the job of composting devours all the Nitrogen it can get it's tiny little hands on ( ), so if you find any warmth in your potting medium when potting up, add a little extra N to be safe. (By the way, if you do feel any warmth (other than the sun sort) in your potting medium you really shouldn't be using it yet, because as I just said, it hasn't finished composting down yet.)

Ken,

it supposedly last only 6-9 months anyway so to me you would have to add other fert anyway unless you do not fertilise over winter ( I do)

As stated above osmocote comes in a range of different release options for different purposes. I use the longest release they make. It is rated at 12-14 months but only available in large bags and, even then, sometimes difficult to get. (My suppliers told me there was no such thing so I had to get Scott's to give them a nudge before I could get some last year)
Osmocote also comes in different tailored release patterns. You can get HiStart which releases more of the fert early then less as time goes on. The standard release pattern releases relatively evenly over the entire time. I have been using LoStart formulation which has a slow release early then builds up to maximum release later in the cycle. I think that should give me less fert for a couple of months after repotting (while trees are still dormant and roots start to grow) then allow more after a couple of months when the trees really need it????
There are also options with and without trace elements so Osmocote is not just Osmocote. There are lots of options and you really need to check which one you are using to get the best out of it

For trees that are repotted less often ( Pines, Junipers etc) then they will get firt for the fist part of a year, then you will have to revert to manual fertilising anyway, so why not just do it manually with Liquids and pellets / cages from the start.

Scott's (the makers of osmocote) also recommends the best way to apply it is to dibble holes into the mix and fill with the prills. That's how I apply it in 2nd and subsequent years - push the root shears into the rootball and twist to open up a hole then fill with fresh osmocote to ensure ongoing slow relase fert for when you get busy (or forget)
Note that I also add supplementary fert through the growing season which does give me better growth and health.

Mixing it with the potting mix is their second option - not sure why it is not the preferred method

shibui wrote:Mixing it with the potting mix is their second option - not sure why it is not the preferred method

Maybe it's because it's not necessarily evenly distributed, depending on how you mix it? If you drill holes at least you can get it where you want

Another possibility is that if mix with slow release in it is stored damp the fert starts to release but, with no roots to use it or water to leach it, can build up to toxic levels by the time you plant into it. Drilling into the pot means it only releases ferts when you need it.
Direct drilling into pots would also encourage second and more applications in longer term production so they would sell more?

That sounds quite plausible too

Interesting idea Shibui and never thought of that.

Ken

I've often wondered about the worth of the potting medium manufacturers sticking the pellets into bags of potting mix as well. I've crushed a pellet every now and then and they have been empty, or near to it sometimes.

Graeme wrote:Once it starts to break down it will also get so hot as to burn the roots of your tree.

Don't underestimate the heat generating capacity of decomposition! I work on a pig farm and last week we had a pile of manure spontaneously combust! (Shouldn't be any danger of that in your pots, this pile was 4m high, 6m wide and 50m long) The recent rains and a string of warmer days created a "perfect storm" of sorts. We're still digging it out and spreading it to stop it smouldering...

P.s. Burning pig manure smells about as bad as you'd expect