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Ah, dahlias! These stunning, vibrant flowers are a favourite in gardens everywhere, known for their bold colours and intricate blooms. They can transform any garden into a floral paradise. Whether you love tropical, cottage garden or just elegant sophistication they will always fulfil the brief. But here's the thing: while they are beautiful, they also require a bit of TLC, especially if you’re committed to gardening sustainably. Sustainable gardening and dahlia care is all about nurturing your garden while being kind to the planet, and when it comes to dahlias, eco-friendly fertilising and watering techniques are key.
In this post, we’ll dive deep into sustainable dahlia care. From creating your own organic fertilisers to implementing water-efficient irrigation techniques, we’ve got all the tips you need to maintain a lush, healthy dahlia garden without harming the planet. So, let’s get started on this green journey together!
The basics of dahlia care
Dahlias are sometimes thought of as one of the divas of the garden world. Yes, they have specific needs, but when those needs are met, they truly shine. And those needs are not too demanding. These beauties prefer well-drained, fertile soil, plenty of sunlight (at least six hours a day), and a climate that doesn’t get too frosty.
If you live in an area with harsh winters (like the UK) and you have clay soil, you’ll need to dig up and store the tubers indoors until spring. Otherwise a THICK mulch might be all it takes to keep them protected.
Importance of sustainable practices
Why go sustainable? Well, traditional gardening methods often rely on techniques, synthetic fertilisers and excessive water usage, which can harm the environment. By embracing sustainable practices, you not only grow healthier plants but also contribute to the well-being of our planet.
Eco-friendly gardening helps reduce pollution, conserves water, and promotes biodiversity. Plus, it’s incredibly rewarding to see your garden thrive knowing you’ve nurtured it responsibly and you are part of doing your bit to save the environment and climate change.
Soil health and its role in dahlia care
Healthy soil is the foundation of a thriving garden. It’s not just dirt; it’s a living ecosystem teeming with microorganisms that support plant growth. That is why I practice no-dig gardening here at Bramble + Beyond.
The ideal soil for dahlias is rich in organic matter, which helps retain moisture and provides essential nutrients. Good soil structure is the key to providing this and it also improves drainage, preventing water from pooling around the tubers, which can cause rot.
Here are few ways you can help to improve your soil health.
Using mulch to retain moisture and improve soil health
Mulching is a gardener’s best friend. By adding a layer of organic mulch (like straw, wood chips, or compost) around your dahlias, you help retain soil moisture, suppress weeds, and improve soil structure as the mulch breaks down. Mulching also moderates soil temperature, keeping the roots cool in summer and warm in winter.
I’ve found that mulching during the growing season with Strulch also lessens any problems you may have with slug and snails attacks. Which I have covered in detail in my post on how to manage pests on dahlias.
Apply a cozy 2-3 inch layer of mulch around your dahlias, leaving a little gap around the stems to keep them happy and rot-free. Keep an eye on the mulch and add more as needed throughout the growing season to keep everything in tip-top shape.
Testing and amending soil for optimal dahlia growth
Regular soil testing can provide valuable insights into the nutrient levels and pH of your soil. Based on the results, you can amend your soil with organic matter or natural fertilisers to create the perfect growing conditions for your dahlias.
However, I find that simply adding a regular mulch of compost, well-rotted manure, or other organic amendments keeps everything well balanced, nourished without the need for regular testing and adding additional amendments (which are covered in more detail below).
I usually just cover the soil with a layer of garden compost in the autumn, after digging up the dahlias and this seems to be sufficient for my needs.
Making your own fertilisers
Homemade fertilisers are a sustainable alternative to synthetic shop bought ones, which can deplete soil health and harm beneficial microorganisms.
You’d be surprised how many valuable nutrients are hiding in your kitchen scraps! Eggshells provide calcium, coffee grounds add nitrogen, and banana peels are rich in potassium. These common waste items can be composted or turned into liquid fertilisers to nourish your dahlias.
Or, these same components can be added in their un-composted form in small amounts to deter slugs. I think I am obsessed with slugs!
Here are a few ways you can feed your soil, without reaching for chemicals.
Composting
Compost is a gardener’s gold—it enriches soil with essential nutrients, improves soil structure, and enhances its ability to retain moisture. Compost also promotes the growth of beneficial microorganisms that help protect plants from diseases.
To create compost, start a compost pile or bin with a mix of green (nitrogen-rich) and brown (carbon-rich) materials. Turn the pile regularly to aerate it and speed up decomposition. Once the compost is ready (it should be dark and crumbly), spread it around your dahlias as a nutrient-rich mulch or mix it into the soil before planting. I’ll cover composting in more detail in a subsequent post.
Green manures and cover crops
Green manures and cover crops are plants grown specifically to improve soil health. It is thought that soil prefers to be utilised rather than being left bare to the elements, so planting a cover crop can add organic matter, prevent soil erosion, and suppress weeds. Common options include clover, comfrey, phacelia and legumes.
Sow green manures or cover crops in autumn or early spring. Once they’re established, you can cut them down and incorporate them into the soil a few weeks before planting your dahlias. This practice enriches the soil with organic matter and nutrients. It also creates an early mulch for the soil to prevent weed growth.
For liquid fertilisers, steep some of your cover crop, comfrey is ideal for this, in water for a few weeks. Cover the mixture with a lid and place it somewhere out of the way, it is going to get very smelly! After about 3-4 weeks strain the mixture and dilute it with more water before applying.
Natural soil amendments
Natural amendments, like bone meal, fish emulsion, and kelp, provide essential nutrients for dahlia growth. Bone meal adds phosphorus, fish emulsion supplies nitrogen, and kelp provides a broad spectrum of trace minerals. Apply these amendments according to package instructions, mixing them into the soil around your dahlias.
I have to put my hands up and admit that I rarely apply additional fertilisers to my soil during the growing season. I find that the compost layer I add in the autumn/winter, provides sufficient nutrition to the soil to support healthy growth and masses of flower production. However, this year (2024) has been the exception and I have applied a liquid seaweed feed a couple of times, as the plants have been so damaged by slugs that I felt they needed a bit of extra support.
Water-efficient irrigation techniques
Dahlias need consistent moisture, but they don’t like to sit in waterlogged soil. It’s a delicate balance—too little water can lead to poor growth and fewer blooms, while too much can cause root rot.
On average, dahlias require about 1 inch of water per week, but this can vary based on weather conditions and soil type.
Along with my fertilising approach, my watering approach is similar. I don’t tend to water my dahlias much after they have been planted out, unless there has been no rain for more than a week. Which in the UK is not likely even in the summer months. This may not be the case for warmer climates.
Obviously, if your dahlias are in pots then they need to be fed and watered a lot more frequently as the compost they are growing in will become quickly depleted over the growing season.
Here are some methods of watering that might help conserve water. I also cover watering techniques in more depth in this post.
Drip irrigation systems
Drip irrigation delivers water directly to the plant roots, reducing water wastage and minimising evaporation. It’s a highly efficient way to keep your dahlias hydrated without overwatering.
Setting up a drip irrigation system involves laying out tubing along your garden beds and attaching emitters near each dahlia plant. You will need to check the system regularly for clogs or leaks to ensure it’s working efficiently. You will also need to adjust the water flow as needed based on your dahlias’ growth and weather conditions.
Rainwater harvesting
Any container can collect rainwater, and rain barrels are a simple and effective way to harvest rainwater. I use some old whiskey barrels and a cattle water tank as my main sources of water storage. Place your chosen container under downspouts to collect runoff from your roof.
You can also install a more elaborate rainwater harvesting system with underground storage tanks if you have the space and budget.
You can now water your dahlias with harvested rainwater to conserve tap water and reduce your water bill. Rainwater is naturally soft and free of the chemicals found in treated water, making it ideal for your plants.
I find it is much quicker to have a rain water capture system with an opening where you can dunk in your watering cans rather than having to use a tap to fill your watering cans. When you are watering a full cutting patch, no one has time to stand around waiting for the cans to fill up!
Best practices for watering dahlias efficiently
Timing: Water your dahlias early in the morning to reduce evaporation and give the plants time to absorb the moisture before the heat of the day. This also prevents creating a moist environment as night approaches, which would encourage slugs.
Deep watering: Water deeply to encourage strong root growth. Shallow watering can lead to weak roots that are more susceptible to drought and stress.
Monitoring soil moisture: Use a soil moisture meter or simply check the soil with your fingers to ensure it’s consistently moist but not waterlogged. Adjust your watering schedule based on weather conditions and soil moisture levels.
Seasonal tips for sustainable dahlia care
Your approach to fertilising and watering your dahlias will differ based on the season. Here are some general approaches of what you should be doing in each season.
Spring: As the weather warms, prepare your garden beds by adding compost and organic amendments. Plant your dahlia tubers after the last frost date, spacing them according to their size and growth habits.
Summer: Mulch your dahlias to retain moisture and reduce weed competition. Monitor for pests and diseases, addressing any issues promptly with organic methods.
Autumn: In cooler climates, dig up and store dahlia tubers before the first frost. In milder climates, you can leave the tubers in the ground, covered with a thick layer of mulch to protect them from cold snaps.
Winter: If you’ve dug up your tubers, store them in a cool, dry place. Check on them periodically to ensure they’re not drying out or rotting. Plan your garden layout for the next growing season and prepare any new beds.
Sustainable dahlia care is not only possible but incredibly rewarding. By using homemade fertilisers and water-efficient irrigation techniques, you can grow beautiful, vibrant dahlias while nurturing the environment. From making your own compost to setting up a drip irrigation system, these eco-friendly practices ensure your garden thrives without harming the planet.
Gardening sustainably may seem like extra work, but it’s worth it. Every step you take towards eco-friendly gardening helps create a healthier, more resilient garden and a better world for future generations.
Have you tried any of these sustainable dahlia care techniques? Share your experiences and tips in the comments below—I’d love to hear from you!
Tips for growing your dahlias
- Divide your dahlias: To produce good sized productive dahlia plants, it is a good idea to divide the tuber every few years. If the tuber is too large, then you get increasing amount of foliage and poorer quality blooms.
- Starting your dahlias: From March onwards you can start your dahlias tubers growing in pots in a protected growing space. The space doesn’t need to be heated, but it does need to have light and be protected from frost.
- Propagate your dahlias: Once your potted up dahlias start producing more than 5 new shoots you can take cuttings of any of the extra cuttings, to create new plants that will flower and create a tuber within this growing season.
- Pinch out shoots: Once you have stems that have a few sets of leaves, then pinch out the growing tip. This will encourage the plant to produce more lateral growth and flowering stems.
- Planting: When planting your dahlias, plant out the plants deep enough to cover the tuber. Place the tubers about 15cm (6 inches) deep. Space the tubers/plants about 40cm – 70cm apart. Only plant out once the risk of frost has passed. In the UK this is generally mid May.
- Watering: After planting, water them in well. After the initial watering, I prefer to water all my plants (if I need to water) with a long deep drink, rather than a light consistent watering. I think this encourages the plants to go in search of their own water, making them more drought tolerant.
- Provide support: Dahlias, especially tall varieties, will need staking or other support to prevent them from toppling over under the weight of their blooms. It is best to get this in place before you need it, rather than waiting until it is too late.
- Protect from pests: Avoid chemical pesticides in your dahlia bed. Instead, encourage beneficial insects, try companion planting, use physical barriers, or try homemade, eco-friendly sprays.
- Protect from frost: In the autumn, after the first frost, either cut back your dahlias and mulch heavily to protect the tubers over the winter. Or lift them and store them somewhere cool and dry overwinter.
