Are Coffee Grounds Good for Magnolia Trees?

Magnolia tree with white flowers on bare branches

The Spruce / Autumn Wood

Many readers have heard that coffee grounds are good for a magnolia tree, so they wonder if they should spread them around their tree. Is the alleged benefit a myth or a fact? And, if a fact, exactly how can this kitchen refuse help your plant?

Are Coffee Grounds Acidic?

Magnolia trees (Magnolia spp.), generally, are among the plants that prefer a soil pH that is acidic. That is the reason why some folks who have a soil that is too alkaline are attracted to the idea of sprinkling coffee grounds on the earth around their magnolia trees. They have heard that coffee grounds are acidic, so they figure that they can acidify the soil in this way. And the concept makes sense to them because the coffee that we drink is highly acidic—something to which anyone who suffers from an upset stomach after drinking a cup of coffee can attest. But when we move the discussion from the realm of food and drink to that of gardening, it is not quite so simple. For one thing, we must break the matter down into two separate questions:

  1. Are fresh coffee grounds acidic (that is, the granules inside that can of coffee that you buy at the grocery store before you use them to make a cup of coffee)?
  2. Are used coffee grounds acidic?

Fresh coffee grounds are, in fact, acidic. Problem is, gardeners rarely have fresh ones in mind when asking this question because fresh coffee grounds have value in the kitchen. It would occur only to people who do not drink coffee to use fresh coffee grounds in the garden. By contrast, used coffee grounds are not very acidic; they are more or less neutral, pH-wise.

Even if you are thinking of sprinkling fresh coffee grounds around your magnolia tree, you should have a soil pH test done first to try to find out whether your soil is acidic, alkaline, or has a neutral pH. If such a test indicates that your soil is way too alkaline, then, fine, use the fresh coffee grounds around your magnolia tree. Sprinkling fresh coffee grounds around such acid-loving plants will be helpful if the soil in which they are growing is currently too alkaline for them. An application of fertilizer with ammonium-N is another trick used to acidify the soil. But, otherwise, do not apply fresh coffee grounds directly on the earth around your magnolia tree. Further acidifying soil that is already acidic enough might be counterproductive. 

Other Benefits of Coffee Grounds

So far, we have only discussed how coffee grounds affect soil pH, concluding that it is only the fresh ones that have an impact. Luckily, both fresh and used coffee grounds have other gardening benefits:

  1. If you do not need to make your soil more acidic, you may wonder what you can do with fresh coffee grounds. There is still no need to waste them if you are in the habit of making compost. Why not compost those fresh coffee grounds first? By composting them prior to use in your garden, you will be taking off some of that acidic edge. Both fresh and used coffee grounds will help your compost bin to heat up. The paper coffee filters are fine to compost, too, but they will break down faster if you turn them under in the pile, rather than letting them rest on top, where they will dry out and hang around for a longer time.
  2. Both used and unused coffee grounds contain nutrients that plants need. They are high in nitrogen, and they can also supply your plants with calcium, magnesium, and potassium. For purposes of fertilization, it is better to compost them first, rather than spreading them directly on the ground.
  3. A compost pile made up partly of coffee grounds (whether fresh or used) will draw extra earthworms to your garden, and earthworms are perhaps the most beneficial of the garden critters.
  4. If you grow plants that slug pests tend to bother, such as Hosta ground covers, apply some coffee grounds around the plants. Slugs often (but not always) will leave the plants alone, whether because they dislike the texture, the acidity, or the caffeine of the coffee grounds. Again, if you are using fresh coffee grounds, just make sure that your soil can stand to be acidified a bit. If you are applying used coffee grounds, you do not have to worry.