1. How many gallons of water are you going to give each of your shrubs?
2. A balanced nutrient load is more beneficial than one that is higher in one nutrient than another. What your roses need can only be determined by a good reliable soil test. What is the nutrient load in your soil? What is the humus level in your soil?
3. At best the manufacturers are guessing what your soil might need, and you are mostly guessing what you are doing. Making your soil into a good, healthy soil that wil grow strong and healthy plants is the best way to grow anything. Proper soil pH and a well balanced nutrient load will do more for growing good, healthy plants than any "fertilizer" will.

The numbers are an indication of the percentage of actual element (N, for example) in the container of fertilizer. Organic based fertilizers are usually much lower in actual elements because of the source and packaging processes. Other fertilizers are composed of several different sources (read the labels to see), and are often more packed with actual NPK with very little (if any at all) organic matter.

Thus, 2-3-1 means 2% actual N, 3% P, and 1% K. 15-0-15 would be 15% N and so on.

Actually, the fertilizer analysis can be selected for the crop use. If you are growing a lawn, for example, you will need higher amounts of N than any other element. N is used in large amounts by lawns, and lawns are harvested every week or less.

I'd suggest that there isn't a good reason to use one fertilizer in tandem with another. You could certainly swap the use of one for another occasionally, but don't do double duty. Taking some soil samples to your local extension office for testing is always a good idea, if you have never done so. Over fertilizing your roses, even with organic products, is a good way to set your plants up for insect and disease infestations.

When using a liquid fertilizer, you need to apply enough of the product to insure that the root/soil system has been saturated. Applying a little bit to the surface of the soil or mulch will simply allow it to evaporate.

My understanding of the N-P-K numbers is that they represent the amount in lbs (based on 100 lbs) that is immediately available to the plant. In organic feeding the numbers are low because less of what's in the bag is immediately available. The majority of what's in the bag must be "digested" by some organism in order to be in a form that the plant can take up. This can take a few weeks. The N, P & K are there in greater quantities than 2-3-1, just not immediately available. It's slow-release. Generally, organics don't burn because they don't produce salts which burn and don't hit all at once, and they are only taken up as the plant needs them.

I have not used Neptune yet. When I use fish emulsion products, I either spray enough to coat the leaves or drench with a gallon per plant.

Potash is the K which is good for strong stems. The P is phosphorus which is good for roots and flowers. Phosporus is often already plentiful in the soil. Nitrogen is quickly used up by the organics (composts, manures, etc) that you use so extra nitrogen sources are a good idea.

Sherry

The numbers are not based on 100 pounds. They reflect the PERCENTAGE of ACTUAL N, P, and K in the container, whether it be 5 pounds or 8 ounces or whatever. If the particular product is 2-3-1, then it contains 2% N per, 3%P and 1% K. The rest of the product will consist of a variety of fillers, inert compounds, stabilizers, etc. to equal 100%. 2% of 100 pounds is the same percentage as 2% of any other amount.

Thank you everyone for responding to my question. I think I'm beginning to more thoroughly understand fertilizer and soil better in general. I guess one could tell from my questions that it's all been a little mixed up in my head! Potash versus phosphorus, difference in availability and rate of plant use of each element of the fertilizer, etc. I did have a soil analysis done but need to call Cornell and ask for a little explanation, which they encourage, so I will definitely will take advantage of that. Hopefully, understanding the nutrient status of my soil will help in applying some of the info. I've learned here. Again, thanks everyone!

rhizo-1, you're right. It doesn't matter how much is in the bag. It's a percentage. If 100 lbs is 100%, the 2 of nitrogen would be 2 lbs which is 2%. If the bag is 5 lbs, there is .1 (1/10) lb of nitrogen in the bag. (5 x 2%). We really said the same thing in different ways.

Sherry