I’ve been doing some research for our grapevine and I was curious if our leftover coffee grounds would be good for it. So, I did some more digging. Here’s what I found.
Coffee grounds are good for grapevines since they add nitrogen and some acidity, which grapes prefer. However, there are some concerns about the leftover caffeine in the coffee grounds. Caffeine is a natural pesticide, so some worry about it killing beneficial insects and soil bacteria.
So, while coffee grounds are good for grapevines, how exactly do they help them, and just how many coffee grounds should we use? Let’s take a closer look.
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How Do Coffee Grounds Help Grapevines?
Coffee grounds contain a good amount of nitrogen, phosphorus, magnesium, and copper, all of which are important to maintain a healthy grape plant. They also increase the acidity of the soil, which is helpful for grapevines as they prefer acidic soil with a pH of 5.5-6.5 (source).
The three main nutrients grapevines and most other plants need are nitrogen, phosphorus, and potassium (abbreviated as NPK). Fortunately, coffee grounds provide all three of these nutrients, along with other secondary nutrients such as calcium, magnesium, copper, iron, boron, and zinc (source).
Coffee grounds are also slightly acidic with a pH of 5.5-6.8, which is pretty much perfect for grapevines since they prefer acidic soil.
However, used coffee grounds generally have less acidity than fresh grounds due to the process of brewing (drawing out the acidity).
Used coffee grounds generally have a pH closer to 6.8 (source), which is still great for grape plants. Although, you may need to supplement the soil with additional acidic amendments (more on these later).
So, why is soil pH so important for grapevines?
Without a proper soil pH, the solid nutrients in the soil are unable to be dissolved and used by the plant’s finer roots.
Fourteen of the seventeen essential plant nutrients are obtained from the soil. Before a nutrient can be used by plants it must be dissolved in the soil solution. Most minerals and nutrients are more soluble or available in acid soils than in neutral or slightly alkaline soils.Donald Bickelhaupt, SUNY College of Environmental Science and Forestry
So, if a soil’s pH is either too acidic or alkaline for the plant, it will be unable to absorb nutrients. Over time, this binding of nutrients can lead to leaves and fruit wilting, yellowing, browning, and dropping.
To help with this, when you add any amendments to the soil (including coffee grounds), it’s a best practice to periodically check the soil’s pH.
The best ways to measure the soil’s pH are either with pH strips or a pH meter. I prefer using a meter since they’re affordable and easy to use. If you’d like to see which pH meter I use and recommend, visit my recommended tools page.
If you do find that your grapevine’s soil pH is too acidic (below 5.5), consider adding alkaline materials to the soil like biochar, powdered lime, or wood ash.
On the other hand, if your grapevine’s soil pH is too alkaline (above 5.5), use acidic amendments such as sand, peat moss, and of course—coffee grounds.
Will Coffee Grounds Hurt Grapevines?
Some say that coffee grounds contain too much acidity and caffeine to be used directly with soil. But does this hold any truth?
Caffeine is a natural defense mechanism made by plants to repel insects. This makes it a naturally occurring pesticide. Generally, pesticides can cause more harm than good since they also kill pollinating insects and beneficial life in the soil. However, the science is mixed on the amount of caffeine left in coffee grounds.
As mentioned in the above section, used coffee grounds have much less acidity than fresh grounds due to brewing. Because of this, it would be fair to assume used coffee grounds also have much less caffeine than fresh.
However, some sources mention used coffee grounds can still be harmful to plant and soil life.
So, to stay on the safe side, the best solution here would be to compost your coffee grounds and let the caffeine and acidity break down. After some time in the compost pile, the nutrients should be the only things remaining from the coffee grounds.
Still, if you’re applying a small volume of coffee grounds infrequently, it likely won’t harm the soil.
How To Use Coffee Grounds as a Grapevine Fertilizer
If you have a handful of coffee grounds, you can apply it directly onto your plant’s soil. But if you have a daily pot of coffee, generally more than 1 cup, consider composting it first to decrease the caffeine. Usually, it takes about 2-3 months for the coffee grounds to decompose and become usable by the plant.
Depending on how many coffee grounds you have, and what you prefer, there are a few ways you can use coffee grounds as a grapevine fertilizer:
- Apply it directly
- Mix it with mulch
- Compost it
Generally, you can directly apply a small and infrequent amount of coffee grounds to the top of the grapevine’s soil. Just make sure to spread out the coffee grounds to discourage mold and keep them at least 3 inches away from the plant’s stem or trunk.
However, if you have more than the suggested amounts of coffee grounds above, consider either mixing them with mulch or composting them before applying them to your plant’s soil.
For example, some good mulches to use for grapevines are straw, bark, leaves, and pine needles. Simply mix your preferred mulch and coffee grounds together and apply in a 1-3 inch layer over the soil (under the drip line or canopy of the plant).
Mulching provides the grapevines with a slow release of nutrients, helps the soil retain water, and protects it from the sun and wind. Combined with compost, mulch also greatly helps the beneficial soil life, such as worms and mycorrhizal fungi.
Remember to keep the coffee grounds and mulch at least 3 inches from the plant’s trunk to avoid any mold from spreading.
How Many Coffee Grounds Should You Use on Grapevines?
As a general rule, keep the used coffee grounds below 15-20% of your total soil or compost content. For the occasional espresso brick, you can apply it directly. For the daily pot, consider composting it first. Using an excess with your grapevine or compost pile can create imbalances in nutrients and soil life.
If you’re not sure how many coffee grounds to apply, it’s always a good idea to start with small amounts and work your way up gradually (or you can keep it easy and compost them first).
If you’re composting the coffee grounds first, allow 2-3 months for them to fully decompose. After, apply the compost in a 2-inch layer around your grapevine.
For best results, 2 weeks after you apply coffee grounds, measure your grapevine’s soil pH and check for any growth issues. This isn’t necessary, but it’s recommended if you’re applying large amounts of coffee grounds.
Some signs that you might be applying too many coffee grounds are if your grapevine’s leaves are turning yellow and dropping. This is likely a result of excess nutrients or moisture building up.
However, this is highly unlikely unless you’re using WAY more than the above suggested amounts (generally, above 15-20% of the soil’s total volume).
If you do find that you have extra coffee grounds, and are looking to use them on your other plants, consider giving them to your grapevine’s companion plants.
When Should You Apply Coffee Grounds to Your Grapevines?
The best time to apply coffee grounds to grapevines is in the early spring and throughout the rest of the growing season. Avoid using coffee grounds on grapevines in the winter as the plants typically go dormant and don’t require many nutrients.
If applied in the winter, the coffee ground’s nutrients will go largely unused and simply sit in the soil for several months. With enough time, the extra nutrients and moisture can build up, leading to potential issues such as leaves and fruit discoloring and dropping.
Instead, add coffee grounds to your compost bin (or pile) in the winter and apply the compost in the spring.
Coffee grounds are great for grapevines because they add plenty of nutrients such as nitrogen, phosphorus, potassium, calcium, magnesium, and copper. They also provide acidity to the soil and promote beneficial soil life.
Just as important, coffee grounds also greatly improve the soil’s richness and water retention. In fact, each 1% increase in the richness of the soil can help it hold 20,000 gallons more per acre (source).
Keep in mind to check your grapevine’s soil pH every now and then. If you’d like a visual on how to do so, check out this helpful video below by Alberta Urban Garden!