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Dry alfalfa is a good slow-release source of nitrogen, but since you will be "digesting" it by letting it ferment in water, the resulting tea is a soluble, fast-acting nitrogen source.
Also, by making alfalfa (or manure) tea, you don't have to worry about weed seeds sprouting from the fertilizer.
In addition to nitrogen, alfalfa supplies enzymes and trace elements that are not present in chemical nitrogen fertilizers.
Choose a garbage bin or barrel with no leaks and a tight fitting lid. Position it in an out of the way place - you don't want to have to move it once it's full. For a full size garbage bin (20 gallons) add 16 cups of alfalfa pellets or alfalfa meal (4 cups to every 5 gallons or 22 litres of water)
Add 1 - 2 cups of Epsom salts (magnesium sulphate crystals) (or one quarter to half a cup to 5 gallons) Optionally, add two tablespoons of Iron Chelate
Fill with water, put on a tight lid to prevent mosquitos from breeding in your "swamp"
Let stand for one week until it bubbles with fermentation. Your nose will tell you that it's ready.
Apply alfalfa tea once per month in the spring and summer, especially after the first flush of flowers, to encourage repeat blooming. You can reduce or eliminate the Epsom salts in later batches.
Stop applying it in the fall, when you want the plants to start hardening off for the winter, and don't want to encourage soft new growth.
Put on some old clothes - you're going to get splashed, and you don't want to be socializing with anyone while wearing the alfalfa tea!
Scoop off the liquid with a bucket and apply.
Pour a gallon of tea per rose around the base of the plant; more for large climbers, less for potted roses and minis.
Soak small potted roses in a bucket of tea for 15 minutes each.
When you have scooped off most of the liquid, you will be left with a thick goop of alfalfa in the garbage bin. There are two ways to treat this:
Method A: You can add another quarter-cup of epsom salts, fill the garbage can one third of the way up again, and stir the mix briskly so that the alfalfa is suspended in the water. This slurry can be applied to your roses immediately. Choose the roses in the back of your beds for this tea, where the greenish brown puddle of alfalfa slurry won't be too visible.
Method B: Add the full dose of Epsom salts, refill to the top with water and let sit for another week. Use the liquid, and then bury the alfalfa dregs into your compost pile (by this time they will be pretty smelly)
32 GALLON TRASH CAN
10 CUPS ALFALFA PELLETS (obtained from feed stores)
1 CUP EPSOM SALTS
1 CUP FISH EMULSION
Add the pellets to the trash can. Fill trash can with water. Stir. Cover trash can tightly with lid. For the next three days stir "tea" several times a day in order to dissolve the pellets. Keep covered. On the third day add epsom salts and fish emulsion. It is ready to use on any vegetable, plant, tree or bush.
When all the "tea" is used, there will be enough pellet residue in the bottom of the trash can that you again fill the trash can with water and make more "tea".
Check out comments for a list of all the good stuff in alfalfa tea.