Using 'Kitchen Waste' To Fertilize Plants?

Question:

I want to fertilize my plants with "kitchen waste" instead of chemicals. How do I use coffee grounds for hydrangeas if used grounds are not acidic enough?

Hardiness Zone: 7a

Dorothy from Munford, TN

Answer:

Dorothy,

Used coffee grounds can be spread around your hydrangeas in small amounts and gently mixed into the topsoil, or composted along with other kitchen waste and added to your soil later.

Used coffee grounds are still beneficial to your hydrangeas. Here is why:

1. They contain about 2.0% nitrogen, 0.3% phosphorus, and 0.3% potassium. Just like any organic matter, as used coffee grounds break down they release their beneficial compounds into the soil.

2. When worked into the soil, they do provide a small amount of acidity. Some studies suggest that used coffee grounds lose their acidity when brewed (supposedly all of the acid goes into the coffee). Other studies now suggest that this is not true, and that used grounds do add a small amount of acidity to the soil. The key seems to be working them into the soil and not just spread them on top.
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3. Coffee grounds contain allelopathic chemicals that may inhibit weed growth. It should be noted, however, that these same chemicals are not selective and can inhibit the growth of desirable plants as well.

One thing to keep in mind is that like any organic waste from the kitchen, as coffee grounds decompose, they are likely to tie up a small amount of nitrogen in the soil-making it inaccessible to your plants. How much that affects your hydrangeas depends on how much of the grounds you have incorporated into the soil. In general, a small amount of coffee grounds dug gently into the topsoil around your hydrangeas is probably just fine. Nevertheless, an even better way to utilize it would be to start a backyard compost pile for all of your kitchen waste.

Good luck!

Ellen