Soil amendment. Use freshly cut comfrey leaves (but not the flowering stems in this case—they can root) as fertilizer in planting holes. The leaves break down rapidly and provide nutrients right at the roots.
Compost activator. Comfrey is especially useful if you have lots of dry brown material and the pile is slow to heat up. Just layer the fresh comfrey leaves and stems in as you add other material to your pile.leaves and stems in as you add other material to your pile.
Liquid fertilizer. One of the best ways to tap your fertilizer factory is to brew comfrey tea. Fill a barrel or trash can about halfway with fresh comfrey, add water, cover it, and let it steep for 3 to 6 weeks. Comfrey tea smells foul, so brew it away from sensitive noses (yours or your neighbors). The tea may be used full strength or diluted to about half strength—to the color of weak tea. Use it whenever you water your plants. It's great for watering stressed plants to help get them back on track, reports Jerome Osentowski, director of the Central Rocky Mountain Permaculture Institute, in Basalt, Colorado.
You can also make liquid fertilizer concentrate by packing fresh-cut comfrey tops into an old bucket, weighing them down with a big rock or a plastic bag of water, covering tightly, and waiting a few weeks for them to decompose into a lovely thick black goo. Some gardeners put a hole in the bottom of the bucket and collect the concentrate in another container as it drips out. Dilute this comfrey concentrate about 15 to 1 with water, and use as you would comfrey tea. You can seal this concentrate in plastic jugs until you are ready to use it.
Pest prevention and control. Scientists at Moscow State University in Russia observed that powdery mildew spores that landed on wheat seedlings sprayed with comfrey tea did not germinate, and the wheat seedlings did not become infected. The researchers concluded that the comfrey tea sprays had activated natural defense mechanisms in the wheat seedlings, making them more resistant to disease. This summer, researchers at the Rodale Institute, near Kutztown, Pennsylvania, are conducting controlled experiments testing comfrey tea as a preventive for powdery mildew on sage grown in the greenhouse.
To use comfrey tea or diluted comfrey extract as a foliar drench or spray, add a few drops of liquid soap (it helps the spray stick to leaves) and apply it to your plants. You can use a watering can with a fine rose, but you'll get better coverage with a garden sprayer. Be sure to strain yourliquid very carefully (let it drip through a large coffee filter) before you put it in your sprayer, or you'll clog up the nozzle before you even get started. When you spray your plants, don't coat just the tops of the leaves; reach under and spray the bottoms, too, at least until the liquid starts to run off.