11 Plants You Should Never Fertilize with Coffee Grounds

Coffee grounds are abundant in the homes of coffee drinkers! This waste product is a valuable garden amendment, though it isn’t best for all crops. Backyard gardener Jerad Bryant shares 11 plants you should avoid fertilizing with coffee grounds.

A man's hand holds a handful of used coffee grounds in front of a flowering lilac bush, a plant that should never be fertilized with coffee grounds, featuring clusters of fragrant purple flowers on woody branches, surrounded by dark green leaves.

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Organic matter is essential for the garden. It provides food for decomposition organisms like bacteria, fungi, and archaea. Coffee grounds inject plenty of organic matter into the garden, offering food for microorganisms to turn into soil.

Though they’re good for compost and decay organisms, they’re not beneficial for plants in their undecomposed state. Used grounds leach compounds that restrict plant growth and they can inhibit water flow in the root zone.

Before learning which plants dislike the grounds, let’s first discover how to use them for peak performance in your garden.

How to Use Coffee Grounds

A gardener's hand scoops coffee grounds from a bowl in a bed of curly red and green lettuce plants, surrounded by mulched soil.
Decompose beans improve garden soil when used correctly.

Grounds work best in the garden after they decompose. Worms, microbes, and other belowground organisms turn the ground beans into humus, a rich soil component. Adding them before they decompose can cause adverse effects like caffeine and acid toxicity.

If you have a compost pile, simply add the grounds when you’re through using them. They’re rich in nitrogen and work well as a green material. For every scoop of grounds, add two equivalent scoops of dry brown material like paper, fall leaves, or straw. Compost requires a good balance of greens and browns to work well.

Compost is the easiest way to turn grounds into humus, though there are other options for gardeners that don’t compost. Try burying the coffee and letting it decompose out of sight. You can also scatter it on top of the ground in thin layers. Rake it in to ensure you spread it evenly throughout the site.

11 Plants That Dislike Coffee Grounds

Decomposed grounds work well for many plants, especially those that love acidic soil. Some species dislike acidic sites and prefer more alkaline conditions. Others function poorly with caffeine, whether in small or large amounts. Avoid fertilizing these 11 common garden species, and reserve those grounds for your blueberries, azaleas, and rhododendrons. 

American Arborvitae

A row of tall, pyramidal trees with dense clusters of upright green needles growing along woody branches.
Thuja plants make perfect living fences with proper care.
botanical-name botanical name Thuja occidentalis
sun-requirements sun requirements Full sun to partial shade
height height 40-60’
hardiness-zones hardiness zones 3-7

American arborvitae are perfect for living fences. They mature into conical shapes, sprouting dense branches with fluffy green foliage. They aren’t acid-soil lovers, though they’re extremely tolerant of winter frost. It’s best to reserve your grounds for other plants that appreciate acidity.

Undecomposed grounds are especially troublesome for arborvitae. Compost them first, mixing them with a blend of other garden waste. Then, use the compost sparingly around the arborvitae. A little is okay, though large amounts may swing the pH out of balance.

Linden

Broad, heart-shaped leaves with serrated edges grow on a tree with clusters of fragrant yellowish-green flowers.
Slightly acidic soil suits these trees well for growth.
botanical-name botanical name Tilia spp.
sun-requirements sun requirements Full sun to partial shade
height height 50-130’
hardiness-zones hardiness zones 3-8

Linden trees decorate sidewalks and forests throughout North America. The American linden tree is native to the eastern U.S., while other species originate from parts of Europe and Asia. They prefer neutral to alkaline soils, performing best without coffee waste.

Though linden trees prefer neutral or alkaline soils, the American linden tree Tillia americana tolerates slightly acidic ones. You may use fully decomposed grounds as fertilizer for this specific species. Apply them sparingly in a mix of other mulching materials.  

Lilac

Vibrant purple flower clusters rise from woody stems, framed by heart-shaped green foliage.
Neutral soil is key to growing vibrant, healthy flowers.
botanical-name botanical name Syringa spp.
sun-requirements sun requirements Full sun to partial shade
height height 4-30’
hardiness-zones hardiness zones 3-7

Lilacs offer whimsical, fragrant flowers in the ornamental garden. They’re short trees or tall shrubs, with deciduous leaves and spring-emerging flowers. The blossoms provide nectar to butterflies and hummingbirds, and the leaves are a nutritious food source for hungry caterpillars. 

Though lilacs need some fertilizer during the growing season, they dislike excess acidity. Most species prefer neutral or slightly alkaline soils to grow roots into. Use well-balanced fertilizers instead to add nutrients to the soil. Lilacs appreciate nitrogen to grow leaves, and phosphorous and potassium to grow roots, flowers, and seeds. 

Hydrangea

Large, rounded flower heads with clusters of small blooms in shades of blue, pink, and purple rise above green foliage.
Compost coffee before using it for vibrant flower colors.
botanical-name botanical name Hydrangea spp.
sun-requirements sun requirements Full sun to partial shade
height height 2-15’
hardiness-zones hardiness zones 3-9

Hydrangeas often appreciate acidic sites! So why wouldn’t you want to fertilize them with coffee? Some species sprout flowers that change colors depending on how alkaline or acidic the soil is. It’s best to use fertilizers with a neutral pH unless you desire acidic soil and the corresponding bloom color. Composted coffee grounds won’t have the desired effect.

When using coffee to fertilize hydrangeas, compost it first to ensure caffeine isn’t still in it. Excess caffeine levels can harm maturing shrubs, causing weak growth and yellowing leaves. Composting coffee allows microorganisms and worms to eat the used beans and turn them into rich, earthy-smelling humus.

Lavender

Woody stems with narrow, silvery-green leaves and spikes of small purple flowers form a compact shrub.
Minimal care and well-drained soil lead to thriving herbs.
botanical-name botanical name Lavandula spp.
sun-requirements sun requirements Full sun to partial shade
height height 1-4’
hardiness-zones hardiness zones 5-9

Lavender fits in with ornamental shrubs and herbal ones. It’s lovely to grow among other sun-loving perennials, while it’s herbal enough to deserve a spot next to the rosemary, thyme, and oregano. Plant a few unique varieties next to a walkway and you’ll smell them every time you walk by. 

These shrubs are low maintenance and require few nutrients to thrive. Excess application of used coffee can cause toxic acidity that hurts the lavender’s roots, and the caffeine can prevent them from thriving. Opt for a sandy, gritty mix for growing lavender, and use fertilizer only if the shrub needs it. 

Thyme

Tiny, oval-shaped green leaves grow along slender, woody stems with small, purple-pink flowers.
Avoid acidic materials around for healthier, thriving herbs.
botanical-name botanical name Thymus vulgaris
sun-requirements sun requirements Full sun
height height 6-12”
hardiness-zones hardiness zones 5-9

Thyme, like lavender, is essential in the herb garden. It’s a low-growing spreader that roots freely along its branch tips. The thin leaves add a pungent, herbal flavor that works well in tomato sauce, soups, and oven-baked dishes. 

While picking thyme, it’s best to avoid using coffee materials around the site. Thyme appreciates neutral or slightly alkaline soil and will fare poorly with the grounds around its roots. Though it likes compost, it doesn’t like acidic compost. Use grounds-free compost or mulch when amending your thyme plants.

Broccoli

Thick, green stems with large, tightly packed florets of greenish-yellow form the head of the vegetable.
Small amounts of composted materials may work for these crops.
botanical-name botanical name Brassica oleracea var. italica
sun-requirements sun requirements Full sun
height height 1-3’
hardiness-zones hardiness zones 2-11

Broccoli, leeks, radishes, violas, and sunflowers were a part of this study that looked at how plants perform with coffee grounds mixed in their soil. All five plants suffered from the grounds at various application rates. Both the caffeine content and acidity levels harmed the growing crops, causing low yields at the end of the trial.

Though the research shows these crops dislike growing with grounds, more research is necessary to determine the effects of composted grounds. You may add them in small quantities. A good way to test how they affect your plants is to mix them in containers or fabric grow bags and experiment with different vegetables during the growing season. 

Leek

Long, slender green stalks with a white bulb at the base and feathery green leaves grow in rows in the garden bed.
Well-balanced organic matter enhances vegetable garden productivity.
botanical-name botanical name Allium porrum
sun-requirements sun requirements Full sun
height height 1-3’
hardiness-zones hardiness zones 5-9

Leeks are onion and garlic relatives with a sweet, buttery flavor. They grow like onions, except their roots never form a bulb. The stems stay long and erect with many layers of soft, oniony flesh. They’re exceptionally cold tolerant, working well in frosty climates where onions struggle to overwinter. 

Though leeks are delicious and easy to grow, they won’t grow well with grounds in their soil. Leeks performed terribly in the trial; they prefer organic vegetable fertilizers rich in nitrogen. The best way to promote health in the vegetable garden is to regularly apply compost or leaf mold. The two materials add organic matter, humus, and nutrients to the soil. 

Radish

Small, round red roots with leafy green tops protrude from the soil.
Try fast-maturing varieties for an early-season harvest.
botanical-name botanical name Raphanus sativus
sun-requirements sun requirements Full sun to partial shade
height height 6”-3’
hardiness-zones hardiness zones 2-11

Like leeks and broccoli, radishes are a plant on the test trial that performed poorly with coffee in the soil. Though coffee makes us gardeners speed up, it doesn’t do the same with radishes! Give them loose, fertile soil instead. They’re a root crop, and their roots bulb better with loose soil than hard clay.

If you have trouble growing radishes, consider trying a quick maturing variety that’s cold-hardy. ‘Cherry Belle’ is a longtime favorite, as it can produce a radish in as little as 24 days. Start seeds a few weeks before your last frost date; they’ll germinate and mature under cool weather.

Viola

Heart-shaped leaves with slightly jagged edges surround tiny vibrant yellow flowers.
Bright flowers add color and charm to your garden.
botanical-name botanical name Viola spp.
sun-requirements sun requirements Full sun to full shade
height height 3-16”
hardiness-zones hardiness zones 1-10

Viola is a widely encompassing genus that includes some of the most famous garden plants. Sweet violets, Johnny-jump-ups, and pansies are all flowering plants in the Viola genus. Commonly referred to as violas, these perennials grow low to the ground and display gorgeous edible flowers. Some species, like sweet violets, emit a pleasant aroma while blooming!

Keep old coffee beans away from violas, as they dislike growing with discarded coffee in the soil. They prefer rich, porous, well-drained soil with plenty of humus. They also like consistent moisture, so water them throughout the growing season to keep them happy and healthy.

Sunflower

A tall, sturdy stem with broad, rough-textured leaves supports a large, round yellow flower with a dark center.
Sun-loving plants appreciate soil without caffeine interference.
botanical-name botanical name Helianthus annuus
sun-requirements sun requirements Full sun
height height 2-14’
hardiness-zones hardiness zones 2-11

Sunflowers originated in North America, though they now grow worldwide! Gardeners love sowing the black-streaked seeds. A single seed grows into a plant that may reach 14 feet tall! Whether cultivating colorful multi-branched sunflowers or yellow giant ones, you’ll want to keep coffee far away from your plants.

Sunflowers performed poorly in the coffee trial. Though they excelled at first, they quickly declined as caffeine leached into the soil. Composted coffee may work better for sunflowers if you mix it with fully decomposed materials like fall leaves, garden waste, and kitchen scraps.

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too much fertilizer. Close-up of a gardener's hand with granular fertilizer over a growing cabbage plant in the garden. A young cabbage plant consists of a compact rosette of large, broad, and lobed leaves that emerge from a central stem close to the ground. The leaves are blue-green in color with a waxy texture and slightly jagged edges. Granular fertilizers come in the form of many small, round, orange granules.

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