First, you're correct in thinking that half as much 20-20-20 will yield a solution the same as 10-10-10 (if it was soluble). Another way of saying it is, 1 tsp of 20-20-20 in a gallon of water yields a solution of the same strength as 2 tsp of 10-10-10 in a gallon of water. Generally though, 10-10-10 formulations are slow release, which is different from controlled release, and 20-20-20 formulas are usually soluble in water. While you wouldn't normally mix 10-10-10 in water, it does contain half the N, P, and K that 20-20-20 contains. A lot of growers are quick to recommend a fertilizer with a specific NPK %, but most are unable to tell you precisely why they recommend it. Often, they will offer the idea that fertilizers with a higher first number (nitrogen) are too high in nitrogen to be suitable for houseplants; but they overlook the fact that the amount of nitrogen supplied has nothing to do with the fertilizer ratio, and everything to do with how much N is supplied by the grower. It's as easy to oversupply nitrogen with 10-10-10 as it is with 24-8-16. Actually though, the consequences of oversupplying nitrogen when using 1:1:1 ratio fertilizers like 10-10-10 or 20-20-20 are considerably more severe because you can't even supply an ADEQUATE measure of nitrogen (using 1:1:1 ratios) with out oversupplying both phosphorous and potassium. The perfect fertilizer program would find the grower providing all the nutrients essential to normal growth in the exact ratio at which the plant uses the nutrients, and at a concentration neither so dilute that deficiencies are limiting nor so concentrated that toxicity or antagonistic deficiencies are limiting. It's actually impossible to come even close to achieving that end when using a 1:1:1 ratio fertilizer, or fertilizers actually providing more than 1/6 as much P as N. After the factoring is done for the fact that P and K are actually reported as P2O5 and K2O in a fertilizers NPK %s, you'll find that fertilizers with 3:1:2 ratios (24-8-16, 12-4-8, 9-3-6 are examples of 3:1:2 ratio fertilizers) supply nutrients in almost exactly the same ratio as the average at which plants use therm. There is a significant variance in the overall volume of nutrients taken up by plants, but only a small variance in the ratio the plants actually use. I grow hundreds of species of plants, indoors and outdoors. I formerly used Miracle-Gro 24-8-16 or 12-4-8, to which I added other nutrients. I now use Foliage-Pro 9-3-6 for every plant I grow. It contains all the essential nutrients in a very favorable ratio. It also gets none of its N from urea, which helps to minimize the impact of low light and helps keep houseplants compact. I know that all sounds complicated to a beginner, but if you have questions, don't be afraid to voice them. Al This post was edited by tapla on Tue, Sep 24, 13 at 9:08

Regarding the mint: Keep in mind that when you planted the mint in the soil the mint lost a lot of its roots -- and definitely all the roothairs (which are responsible for water and nutrient uptake). Water roots and soil roots are not the same in structure. Once the mint gets past the initial shock of the root loss and has grown soil roots, it should do very well. Rosemary: A very difficult plant for most folks to keep alive let alone happy indoors. Some do succeed, however, so hopefully you will be one of those lucky ones. You could indeed experiment with adding a drop or two of liquid fertilizer now and then. If the container the plant is in is clear, then algae will show up at some point. While many people assume that's a bad thing (or simply don't like the looks of it) I have known people who found that their plants did not seem to suffer at all from the presence of algae. They found some plants even seemed to perform better. But if algae is not for you and you wish to continue trying to grow the rosemary in water then consider: 1) using an opaque container (will deprive algae from receiving light necessary for photosynthesis); 2) performing regular (2X/week or more) complete water changes; 3) and regularly thoroughly scrubbing out the container you are using. You might also consider trying semi-hydroponics. (You can find out more about that by either Googling, or popping over to the Hydroponics Forum and doing a search for "semi-hydroponics" or "semi-hydro".)

I waited for those with more knowledge on the subject of plant-specific fertilizers to respond. But, instead David has given you the excellent advice of using a good quality compost. Matoad, you may be looking for experience & info on Shultz, Osmocote, or Peters or some other but I don't really have that. Certainly, I can't think how something like bone meal could harm anything. It will break down slowly and improve soil tilth because of that. Despite my organic veggie gardening, I use Miracle-Gro in the flowers every year. I just see it as having a broader benefit than the 16-16-16 which goes in the beds during the Spring. Plants need different nutrients to grow and bloom and not all of those nutrients will be found in your garden soil. Which ones are lacking can only be determined by a soil test. However, mostly your plants need chlorophyll, sunlight, fresh air, and water since most of the plant ends up as carbohydrates arranged in appropriate ways. Certain nutrients can't be ignored and some required in only minute amounts may be lacking. What to do, what to do?? I find organic fertilizers make infinite sense in the veggie garden partly because they have that broad range of nutrients in their plant & animal (rather than just mineral) origins. Now that these organic fertilizers are leaving the $1/pound price range behind, I'm concerned but will continue to go that route. I'll continue buying in bulk and thereby avoid this $2/pound rate that we are heading rapidly towards. Composted manure is the cheapest route to go but good quality has really gone out the window in my area. I would need to supplement manure with fertilizer anyway. I'll continue to use Whitney Farms and forgo the manure except in my own compost pile. The organic fertilizer is for the veggie garden. Most of the compost, however, is for the flower garden. Mostly, that is a result of where the bins are located. Maybe more importantly, is how little compost I can make out of plant wastes, kitchen parings, and a load of cow manure each year. May as well put it ALL in the dahlias, Sweet Wills, and Canterbury bells and not spread it ridiculously thin, hell-to-breakfast. For all the flowers, I'm continuing to use the 16-16-16 followed with 2 or 3 applications of Miracle-gro before blooming. digitS'

Don't cut off the spoiled foliage, which is where the plant's food is made, until the plant turns around. The burned leaf tips aren't from too much sun - they're from over-watering and/or a high level of dissolved solids (salts) in the soil. If you're interested, you can learn about the basics of indoor gardening by clicking this link. Al