Adding coffee grounds to compost or around roses is often touted as a great way to use a waste product to fertilize your soil conveniently and at a low cost. Whilst there are benefits to adding coffee grounds to your rose garden there are some drawbacks that you need to be aware of…
Coffee grounds can be of great benefit to rose bushes when used in moderation, but go sparingly. Fertilizing your roses with an abundance of coffee grounds can burn the roots of your roses because of the particularly high nitrogen content.
Read on for the benefits of coffee grounds for the soil, how best to apply, and most importantly WHEN to apply this natural fertilizer…
(Do not apply to early or late in these seasons as this will stimulate new growth which will be killed in the first frost of winter, keep reading for more details).
How Does Coffee Grounds Benefit Roses?
The primary available nutrient in coffee grounds is nitrogen. Nitrogen (along with phosphate and potash) is the most important nutrient for healthy roses in the growing season and it is required in large amounts as it stimulates new leaf, stem, and cane growth.
Coffee grounds are a welcome and much-needed hit of nitrogen when applied in the spring for new growth at the start of the growing season and to ensure a more healthy, disease-resistant rose.
Whilst coffee grounds are primarily valued by rose growers for their higher nitrogen content, they also contain other essential minerals such as phosphorus, potassium, and copper, all of which will improve soil health and are valuable nutrients for roses.
Improves Soil Drainage and Feeds the Soil’s Ecosystem
Roses also love organic material (such as coffee grounds and leaf mulch) added to the soil as this will improve the structure of the soil and feed the ecology of the soil such as earthworms and microbes that break down organic material into a form that is easily taken in by the roses roots.
Organic material has the ability to absorb and hold onto water yet let excess water drain freely through the soil, which is perfect because roses need well-draining soil that can also retain water so the roots can draw upon the water in the surrounding moist soil when they need to without the root system being in saturated.
Organic material provides the perfect balance between holding on to moisture and allowing excess water to drain away so the roots aren’t water-logged.
Coffee grounds also happen to be a favorite food of your local worm population. This will benefit the roses as worms effectively aerate compact soil which improves the soil structure and drainage.
In fact soil with a high amount of worm activity will drain 10 times faster than an area with no worms thanks to the channels in the soil that they create which will help your rose avoid root rot if you have compacted heavy soil or slow drainage.
Worms feed on the coffee grounds and the resulting worm casts, concentrate the valuable nutrients and minerals, which increases nutrient availability to the roots of your rose from the surrounding soil.
The tunnels and casts that the worms leave behind allow the roots of your roses to penetrate deeper into the soil so the plant has greater stability, access to moisture, and nutrients for a healthier and more drought-resistant rose.
Coffee grounds are also beneficial for adding to your compost heap as it decomposes quickly and it can add valuable fertile material to be used as mulch for your roses and other plants in your garden during the growing season.
Ensures the Right Soil Acidity
Roses grow best when the soil acidity is in the range of pH 6 to 6.8 with a pH of 6.5 being optimal. Used coffee grounds do differ in acidity depending on the variety of beans used, however, they are generally pH neutral to slightly acidic once decomposed which is perfect for fertilizing roses.
If you are unsure of the pH of your soil, you buy a pH soil tester from Amazon to make sure your soil is in the optimal range.
When to Apply Coffee Grounds (Important!)
As Nitrogen is the primary nutrient in coffee grounds, this makes it perfect for fertilizing roses. But if you apply coffee grounds too early or late in the season then the nitrogen will stimulate new soft delicate leaf growth that will be vulnerable to frost damage.
Wait until April/May to apply coffee grounds when the rose is emerging from its winter dormancy and the new leaves are almost fully open. Coffee grounds should not be spread on rose beds after August 15th as new growth needs time to harden and prepare for the coming winter frosts.
If you do apply any nitrogen based fertilizer after the middle of August the new growth will likely turn black and die in the first frost. If this happens then you need to remove the damaged growth with pruners as soon as you can. As long as you are quick to act the rose should be fine as most rose species are hardy plants.
How to Apply Coffee Grounds as a Fertiliser for Roses (Don’t Use Too Much)
There are several effective ways to help your roses benefit from coffee grounds. However, when fertilizing roses, you must use coffee grounds in moderation. Coffee grounds contain a particularly high concentration of nitrogen.
Whilst nitrogen is imperative for healthy soil and plants, too much nitrogen can actually burn the roots of roses and other plants.
There are three easy ways for your roses to benefit from coffee grounds safely…
- Distribute half a pound of coffee grounds around each mature rose plant and water in with 2 gallons of water (a whole watering can).
By sprinkling around half a pound (2 cups or 500 grams) around the surrounding soil of rose plants you can increase the soil’s nitrogen content without harming the roots. There is no need to dig the grounds into the soil as this could disturb the roots and surrounding soil structure which is why it is better to water in.
Also, as worms love coffee grounds they will do all the hard work for you by pulling it down and working it into the earth. As they digest the coffee grounds they will produce worm casts which are in a form that will be more readily available to the plant to uptake.
Rose beds with a lot of worm activity indicate healthy soil and favorable growing conditions for roses.
You only need to do this once at the start of the growing season (Late April/ early May). If you fertilize your soil too late then this will encourage your rose plant to put on new delicate leaf growth late in the season which will be destroyed in the first frost of winter.
Distributing coffee grounds in this quantity will provide the right amount of nitrogen without any harmful side effects.
Another approach is…
2. Mix half a pound of coffee grounds in a 2-gallon (9 liters) water can
Place around half a pound (2 cups or 500 grams) of coffee grounds into a watering can (standard watering cans have a 2-gallon capacity) and water the surrounding soil of each of your roses. This ensures an even distribution of nutrients to the soil and also saves you the job of watering again.
Place the coffee grounds into the watering can first and then pour in the water. This will help mix the finely textured coffee grounds with the water so that it is suspended and mixed evenly throughout.
Mixing the water with the coffee grounds serves as an effective fertilizer as it encourages the solution to infiltrate into the soil and reach the roots efficiently.
Again I must re-emphasize it is important to do this at the start of the growing season and not towards the end of summer as the hit of nutrients could encourage late-season growth which will get immediately damaged in the first frost of winter.
Also do not exceed half a pound of coffee grounds diluted into your 2 gallons (9 liters) around each plant. This is another good rule of thumb to ensure your roses receive the right amount of nutrients without suffering the side effects of an excessive concentration of nitrogen.
3. Add coffee grounds to your compost heap for a balance of carbon and nitrogen based mulch.
Adding coffee grounds to your compost will ensure that there is an appropriate mix of nitrogen and carbon.
Applying a layer of compost around roses will suppress weed growth, improve the structure of the soil, and increase drainage.
Also, organic mulch such as coffee grounds is great at absorbing water so the roots of your rose can draw upon the stored moisture when they need to.
Compost mulch is best applied around your roses at the start of spring as this is the peak time that weeds will attempt to grow and compete for resources with roses. There is no need to dig the mulch into the soil as this could damage the roots and interfere with the established soil ecology and structure.
Instead, distribute the mulch around the roses around 1-2 inches deep and let the worms and rain work the nutrients into the soil. Avoid piling mulch around the stem of the rose as it could cause the stem to rot, just deep an inch radius around the stem clear of mulch and the rose will thrive.
Where to Source Coffee Grounds
If you are not a coffee drinker yourself one of the best ways to get your hands on used grounds is to simply approach local independent coffee houses.
Most independent stores happily give away used grounds for free as it is otherwise a waste product that they have a surplus of and it saves them having to dispose of it themselves.
You can also try asking at bigger coffee chains such as Starbucks however, established chains often have set procedures of how to deal with waste and they may be less inclined to hand over their grounds!
Often these coffee chains are franchises with independent management so their policy on giving away coffee grounds can vary from store to store.
Conclusion
Coffee grounds help to improve the fertility, drainage, and structure of soils so that roses can thrive and produce a great flower display.
How be careful as coffee grounds can contain so much nitrogen that it is important to go sparingly and only distribute the grounds to your rose bed once in the Spring and to follow the instructions to avoid burning the roots.
Nitrogen is one of the three essential nutrients (the others being phosphate and potash) that roses need in large quantities in the spring when they are in a hurry to put on new growth. So by adding coffee grounds to your rose bed at the start of the season when the leaves of your rose are about to unfold, you will set your rose up to thrive throughout the year with a good show of flowers.