Yes Alfalfa is excellent for your roses, I have used it for years in "Rose Tea"!
DON"T USE SEA SALT INSTEAD OF EPSOM SALT!!!!!
Epsom salts is not a true salt, but really Magnesium Sulfate (I have no idea why they call it salt). If you use sea salt you will destroy your roses!!!!!
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 soluable, 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.
Triacontanol (growth stimulant)
Vitamin A (high concentration)
Amino acids: Tryptophan, Aspartic Acid, Threonine, Serine, Glutamic Acid, Proline, Glycine, Alanine, Cystine, Valine, Methionine, Isoleucine, leucine, Tyrosine, Phenylalanine, Histidine, Lysine, Arginine
Minerals (contained in dry alfalfa): Nitrogen, Potassium, Phosphorus, Calcium, Magnesium, Sulphur, Manganese, Iron, Boron, Copper, Zinc.
In a full size garbage bin (20 gallons) add 16 cups of alfalfa pellets or alfalfa meal. (4 cups to every 5 gallons water)
Add 1 - 2 cups of Epsom salts (or one quarter to half a cup to 5 gallons)
Add 1 cup fish emulsion.
Fill with water, put on a tight lid. Let stand for one to two weeks 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. 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.
Scoop off the liquid with a bucket and pour a gallon of tea per rose around the base; more for large climbers, less for potted roses and minis.
When you are left with a thick goop of alfalfa in the garbage bin, you can either add half a barrell more water, stir and add the slurry to your roses as well, or add the alfalfa dregs into your compost pile.
I have used this recipe for a few years now, and my roses do wonderfully. You can also add some kelp, bone meal, compost or manure to your tea if you would like - roses like them all!
Hope this answers your questions, and eases your doubts!