What Plants Don’t Like Coffee Grounds? A Guide to Using Coffee Grounds in Your Garden

As a passionate gardener and coffee lover I’m always looking for ways to upcycle my used coffee grounds. Coffee grounds contain essential nutrients like nitrogen, phosphorous, potassium and magnesium that are great for fertilizing plants. However not all plants thrive with coffee grounds. Through trial and error in my own garden, I’ve learned that certain plants don’t like coffee grounds.

In this article I’ll share my experience on what plants to avoid using coffee grounds on why some plants don’t like coffee grounds, and how to properly use coffee grounds in your garden.

Why Use Coffee Grounds in the Garden?

Before diving into what plants to avoid, let’s first go over the benefits of using coffee grounds in gardening:

• Coffee grounds loosen and aerate soil due to their gritty texture. This improves drainage and allows plant roots to spread more easily.

• The grounds add organic material to the soil, which improves soil structure and water retention.

• Coffee grounds contain nitrogen, phosphorous, potassium, calcium and magnesium, providing a slow-release fertilizer for plants as the grounds break down.

• The acidic pH of spent grounds helps acid-loving plants like azaleas, blueberries and hydrangeas thrive.

• Coffee grounds deter pests like slugs and snails due to the caffeine.

Using coffee grounds in compost and as a garden fertilizer allows me to repurpose waste from my morning brew into plant food. It’s an eco-friendly, sustainable way to boost my garden.

What Plants Don’t Like Coffee Grounds?

However, through trial and error, I’ve learned that not all plants appreciate coffee grounds. Here are the key plants to avoid using coffee grounds on:

1. Herbs

Many culinary herbs such as basil, parsley, mint, sage and thyme don’t like acidic soil. I found that my herbs struggled when I used coffee grounds as mulch around them. The overabundance of nitrogen and acidity stunted growth.

Better alternatives: I switched to using more neutral composted manure as a fertilizer and mulch for my herbs. Their growth improved dramatically once I stopped using coffee grounds.

2. Root Vegetables

Root crops like carrots, potatoes, sweet potatoes, turnips and radishes develop tubers and swollen roots. These plants thrive in loose, well-draining soil. Heavy, dense soil stunts their growth.

I found that applying a thick layer of wet coffee grounds caused the soil around my carrots and potatoes to become compressed. Their roots couldn’t properly expand, leading to stunted vegetables.

Better alternatives: I achieved much better results by mixing coffee grounds into fast-draining compost before applying around root crops. This prevented overly dense soil.

3. Beans and Peas

Legumes like beans, peas and soybeans have a special symbiotic relationship with rhizobium bacteria in soil. This bacteria helps legumes fix nitrogen from the air into ammonium compounds their roots can absorb.

I learned the hard way that the acidic pH of coffee grounds compromises rhizobium bacteria, interfering with nitrogen fixation in beans and peas. My plants became nitrogen deficient after using coffee grounds.

Better alternatives: I switched to using more gentle, neutral compost and manure fertilizers around my beans and peas. Their growth and nitrogen levels improved.

4. Flowers Prone to Fungal Diseases

Flowers like roses, marigolds and zinnias are prone to fungal diseases like powdery mildew, rust and botrytis blight. The damp, acidic environment created by coffee grounds encourages fungal spore growth.

I noticed my roses developed worse powdery mildew after mulching with coffee grounds. The excess moisture and acidity aggravated their fungal problems.

Better alternatives: For disease-prone flowers, I avoid wet coffee grounds. Instead, I mix small amounts of used grounds into fast-draining compost before top-dressing around these plants. This prevents over-acidification and fungal issues.

5. Most Houseplants

Indoor plants evolved in tropical environments, so most houseplants thrive in neutral to mildly acidic soil with pH levels around 6-7. Exceptions are acid-loving plants like orchids and gardenias.

I learned the hard way not to use my morning coffee grounds to fertilize my houseplants after they started yellowing and dropping leaves. Turns out, the acidic pH and excess nitrogen from the grounds burned their roots.

Better alternatives: Most houseplants do better with a balanced, mild organic fertilizer or compost tea instead of fresh coffee grounds. I only use spent grounds for my orchids now.

Why Don’t Some Plants Like Coffee Grounds?

Now that we’ve covered which plants to avoid using coffee grounds on, let’s explore the reasons why some plants don’t like coffee:

1. Acidic pH

The pH of used coffee grounds ranges from 4.5-6.5, making them quite acidic. Not all plants thrive in acidic soil. As mentioned above, herbs, beans, peas and most houseplants prefer neutral soil around 6.5-7 pH. Too much acidity damages their root systems.

2. Excess Nitrogen

Coffee grounds contain 2-3% nitrogen in forms that plants can readily absorb. While nitrogen encourages leafy growth, too much can burn plant roots and leave them deficient in other nutrients. Plants adapted to low-nitrogen conditions like herbs and flowers can easily get nitrogen toxicity from coffee grounds.

3. Increased Moisture Retention

The organic matter in coffee grounds retains moisture, which benefits drought-tolerant plants. But as mentioned, this moisture encourages fungal diseases in plants prone to powdery mildew and blight. Wet grounds also compress soil, which harms bulbing vegetables.

4. Contains Caffeine and Other Compounds

In addition to key nutrients, coffee grounds contain caffeine, polyphenols and acidic compounds. At high concentrations, these components can damage sensitive plant roots, even if the grounds are aged or composted. Some plants like beans simply don’t thrive in the complex chemical environment created by spent coffee.

By understanding these key reasons, we can see why moderation and proper application technique is essential when using coffee grounds in the garden. Too much of a good thing can quickly cause problems.

How to Properly Use Coffee Grounds in Your Garden

Now that we know what plants don’t like coffee grounds, let’s discuss some best practices on how to use spent coffee appropriately:

• Test your soil. Use an inexpensive soil testing kit to determine your garden’s pH and nutrient levels first. This helps identify which plants will benefit from coffee grounds versus those that won’t.

• Use in moderation. Coffee grounds are very concentrated sources of nitrogen and other nutrients. Use them sparingly, no more than a 1⁄4 inch layer twice a season. Too much too fast can burn plants.

• Mix with compost or manure. Before top-dressing or tilling into soil, mix spent grounds with compost, manure or leaf litter. This balances pH levels and controls nutrient release rates.

• Avoid wet coffee grounds. Always let grounds fully dry and break up any clumps before applying. Wet grounds compress soil and foster fungal issues.

• Monitor plants. Observe how your plants respond, and adjust your coffee ground application accordingly. Temporary nitrogen toxicity or fungal issues can arise if over-applied.

• Talk to your local nursery. Consult with staff at your local nursery to identify plants best suited to used coffee grounds in your specific climate and soil conditions. Local expertise can help you avoid potential issues.

Plants That Love Coffee Grounds

To finish this guide, let’s look at some plants that thrive with used coffee grounds:

• Tomatoes: The nitrogen and magnesium in grounds encourage prolific fruiting.

• Peppers: Scoop ripe peppers out of wet grounds for a perfectly supported harvest.

• Carrots and Beets: Grounds lightly mixed into sandy soil improves moisture retention for these root crops.

• Squash: Grounds deter squash vine borers.

• Berry Bushes: Acid-loving blueberry and raspberry bushes produce more fruit with grounds.

• Citrus Trees: The acidity and nitrogen benefits citrus growth.

• Rosemary and Lavender: These Mediterranean herbs tolerate the pH and like the extra nutrients.

• Bougainvillea: The acidity from coffee grounds makes these tropical vines bloom vigorously.

Through proper application and moderation, spent coffee grounds can be a wonderful asset in the garden. Correctly using grounds provides sustainability along with growing benefits for many plants. With a little care and observation, gardeners can keep their grounds out of the trash and in the soil where they belong.

Hopefully this guide gives you a helpful overview on how to appropriately use your morning coffee waste to enrich your garden soil and plant growth. Always monitor how your specific vegetation in your unique climate responds, and avoid piling on grounds in excess. With the right plants and care, repurposing your leftover coffee into plant food is a great way to close the loop and upcycle in your green space.