Nutri-Cote and Osmo-Cote type products are fertilizer in coated time / temperature release pellets or beads that release a little fertilizer with every watering. Both recommend applying some quantity based on pot size (volume) and replenishing the pellets every 60 days in warm weather 90 to 120 days in cool weather. This is MUCH MORE CONTROLED than just sprinkling soluble fertilizer on top of your media. I
1. Water soluble fertilizers dissolved into your irrigation water give you the greatest control over your fertilization program. You can know with certainty the parts per million or mg /liter dose rate of Nitrogen, Phosphorous and Potassium (K) if you choose to do the maths.
2. second best is the time release fertilizer pellets such as Nutri-Cote and Osmo-Cote type products. These are pretty good. Except one must keep in mind that release rate is governed by temperature. In cold weather they will not make enough of their nutrients available for cold weather growing species, like spruce and firs. In hot weather, especially when we have temps above 100 F or 40 C they will tend to dump much of their contents very quickly. This can be a problem in hot summers. If you put these pelletized fertilizers in mesh bags, and place the bags on the soil, then it is easy to remove the fertilizer during excessive heat waves. This takes care of the problem of temperature release of the fertilizer.
3. the all organics - these are good, it is difficult to get enough nitrogen from "all organic" fertilization, but you can get nice healthy short internode growth, this is good for bonsai, but won't win the "biggest pumpkin or beefsteak tomato" contest. Upside, fertilizer burn is unlikely, even with fairly heavy organic fertilization. Downside, most organic fertilizers leave behind fine particle waste. This fibrous material eventually "plugs up" drainage. Heavy organic fertilization can force you into having to repot a tree sooner than you might want to. putting cake type fertilizers into mesh bags does trap much of this waste, but not all. Also having the fertilizer in bags allows one control, you can put on more or take all the fertilizer away simply by adding or removing bags. In Japan pines and many conifers are potted in nearly all mineral potting mixes, pumice and such. These organic fertilizers become the source of soil organics that feed the mycorrhizae and create a healthy soil microbiome. Myself, I have been transitioning to more and more organic, though I do sell chemical fertilizers to the orchid community, and do cross over a little into the bonsai community with my chemical fertilizer sales. Rape seed cake, sugar cane bagasse, cottonseed meal and other seed meals are typical organic pellet or cake fertilizers. Composted manures can be used, composting is important because fresh manures can be high in salts and attract animals that dig, racoons, skunks, an other destructive vermin. Actually skunks are likely after earthworms and beetle larvae, both of which can be found in manures that are in various stages of composting. I like liquid fertilizers, because I created a set up for easy dosing and easy control of dose rate. Its not an "easily transferable" set up, unique to my house, so I won't go into detail. But for liquid applications I like Fish Lysate by Dramm (as superior to Fish Emulsion) and any of the various Kelp Extracts.
4. As aptly described by
@rockm , just sprinkling soluble fertilizer on top of the potting media is a really, really bad idea. Sure, one can get lucky. Might even get lucky for quite a number of plants for a number of years, but it can go oh so wrong. Its no big deal to loose a juniper in a nursery pot you bought 3 months ago. It is another matter to loose a juniper you might have been nursing for 40 years in your care. Just sprinkling soluble s**t on top of your soil you will never get to the point where you can point to a tree you have been caring for, for over a decade or two. Respect the time you have put into your projects. Respect the time you WILL in the FUTURE be putting into your projects.
