You have basically two sorts of fertilizers: organic and inorganic. Both have their zealots. The main disadvantages of organics are nearly every source of organic fertilizer is animal (and people) food. If you have wild life (coyotes, raccoons, squirrels, rats, etc.) and use blood meal, bone meal, even alfalfa, they WILL find it attractive and will often dig up the area looking for the "food". Count household dogs in that group, also. I can't use organics because the three dogs go berserk looking for the "food". Organics also require appropriate soil temperatures and moisture levels for the bacteria and fungi to "digest" it into the salt forms, which are the forms plants are able to absorb through their feeder roots and literal green parts, so if you live where it's too cool, too wet, too dry, they may not provide you with the speed of benefit you desire. If you live where it's too hot, they can be digested quickly and then produce the 'feast and famine' effect of too much food followed by too little. But, they do help build soil and feed soil bacteria and fungi, producing a healthier soil. Inorganics are usually less costly; they store longer as long as they remain dry and they act much more quickly than organics because they are already in the form the plants require to be absorbed. If you have a chlorotic, nitrogen/iron deficient plant showing the characteristic yellowing leaves and want to "green it up" quickly, inorganic fertilizers applied by the label instructions, will provide that greening much more rapidly than organic. And, no animal will be attracted by the inorganic fertilizer. You have pelletized as well as water soluble inorganics. Use both with caution and only by the label instructions as being salts, if applied incorrectly, you can literally burn and kill plants with them.
No matter what type you use, always water the plant well a minimum of several hours (preferably the day before so it's turgid, full of water) before fertilizing. NEVER allow any fertilizer type to rest against the shank or canes of the plant as they all can damage and even kill the plant as they dissolve. It is safest to apply fertilizers in the "drip zone", where rain will run off the perimeter of the plant and fall to the soil in the greatest concentration. That's where the feeder roots are at their densest as that is where Nature provides the most water. Pellet types are best applied there so as they dissolve with the higher moisture levels, they wash through the feeder roots to be absorbed better. That is also where organics will find the best soil temps and moisture levels to provide the most efficient "digestion" by the soil flora and fauna. If you're using a water soluble type, you can literally "rain" on the plant as the salts can be absorbed by the foliage and canes as well as by the roots.
So, if you want the fastest results for your young plants, provide a good potting soil and either a time released type (Osmocote) so small amounts of nutrients are leached from the pellets with each watering over an extended time, or, my favorite for young plants and seedlings, a water soluble type applied "weakly, weekly". The traditional instructions for most water soluble types has long been a tablespoon per gallon applied every two weeks. Nitrogen flushes through the soil with irrigation water, so much of it is lost when you water. A more consistent application of nitrogen will keep plants growing at a steadier rate. I'll use half a tablespoon per gallon, applied weekly, "weakly, weekly" to them so they mature and develop faster. As long as they are properly watered BEFORE any "salts" are applied, and the "salts" are applied in the appropriate concentrations, it's impossible to burn the plants with too strong a dose. It requires more time and effort on your part than an application of Osmocote every two or three months, but you're likely hovering over the new roses anyway so tending them like this may easily fit in with your time and energies. Once you have more of them or they are larger and not "babies", you can easily switch to whatever types fit your budget, time and energy.
Fish emulsion is a good product, but it is not balanced. Whatever you use, read the guaranteed analysis of the product. The main numbers to pay attention to are the N-P-K (nitrogen, phosphorus and potassium) levels as those are the main indicators of what type the product is. Fish emulsion is often rated as 5-2-2. Some products vary a little. This says that product has a guaranteed level of 5% Nitrogen; 2% phosphorus and 2% potassium. Very basically, nitrogen stimulates growth; phosphorus stimulates flowering and potassium stimulates formation of fruit. Of course there are many other functions each stimulates but viewing them this way helps determine which type you want for what function. The three major types you will encounter are "lawn", "tomato" and "acid". Lawn and acid share a common trait, both are extremely high in nitrogen as that "acidifies" the soil which releases more of the nutrients locked up by alkaline compounds. Grasses mainly need nitrogen to grow and turn green. Acid loving plants such as azaleas, camellias and gardenias evolved in areas with acidic soils and waters so if grown where conditions are more alkaline, they require acid types to flourish. Roses basically love tomato type fertilizers, those with higher phosphorus levels than the other two nutrients to stimulate them to flower more than grow or set fruit. "All Purpose" types generally have fairly equal levels of N-P-K, such as 12-12-12. Those can be used for roses and other non acid loving plants but may provide more salts and nutrients than needed and can more easily burn due to the higher nitrogen levels.
Being told time release types will turn the soil "toxic" is a bit disingenuous. ANY product applied improperly can damage, even kill plants and "poison" the soil. As long as whatever is used is applied by the label instructions and the soil, whether in the ground, in planters or pots is properly watered so the salts are flushed through them and either deeply into the ground so they are filtered out by the soil or run out the drain holes and are flushed away from the plants, the plants should grow and flower well. Not allowing the drainage water to flush out and away from the pot will increase the salt levels in that soil ball and will eventually inhibit or even kill the plant in the pot. If the drainage water is caught in a saucer so it is drawn back into the pot, each time you water, you're adding salts from the irrigation water. Add fertilizers and you add more salts. The saucer now has salty water in it and when drawn back into the pot, some evaporates off the soil surface and some is absorbed by the plant. Each time that is repeated, it mimics a soup which is boiled all day long to keep it hot, as water boils out into steam the salty soup gets saltier and saltier as the water is boiled out of it until it's too salty to eat. If you've grown house plants and noticed the beige deposits on the soil surface and pot sides, that's the salts building up because the water isn't permitted to flush them out and away from the soil ball. It works the same way outdoors in potted plants. Edit: I also meant to add, this is the disadvantage of "drip irrigation" for areas with alkaline soils, particularly those which have drainage issues. You keep adding "salty" water in too small amounts to flush the salts through the soil, so it builds up in the root zones until the plant is struggling in salty soil. Actual water, so it flushes the salts through the soil and pushes carbon dioxide out of the soil and draws oxygen into it is what Nature provides and what we are best benefited by replicating. I hope I've explained what I was trying to explain sufficiently to help.
