The best mulch for dahlias: a comprehensive guide

Mulching your dahlias is one of the best ways can keep your dahlias healthy and growing strongly throughout the summer.

In truth, mulching benefits all plants in your garden but there are lots of different mulches that you can use. So, when choosing the best mulch for your dahlias, it’s essential to understand the purpose of mulching and consider the options available to you and how they might benefit your plants in your situation.

Best mulch for dahlias?

In this post, we’ll look at what mulch is, the various types of mulch, the benefits to your dahlias of using mulch, as well as how and when to apply mulch to your dahlia plants.

Whilst there are a number of specific mulches you can use for your dahlias (see further below), the biggest distinction is between organic mulches, like compost or wood chips, and inorganic mulches like plastic sheeting or weed suppressant fabric.

The inorganic mulches tend to be used more by dahlia farms and commercial dahlia growers, where visual effect is secondary to crop protection and maintenance. They can be removed at the end of the growing season for the lifting of tubers and the soil is then tilled and fed.

For home gardeners, in my experience, organic mulches are simpler and more convenient. I therefore think they are the better type of mulch for use with your dahlias. They are more effective in conditioning the soil in the garden beds  over the growing season, more convenient to apply, and more visually appealing.

If you are growing dahlias at home for exhibition purposes, you might want to follow the more commercial practices. But, interestingly, David Gillam, writing for the UK National Dahlia Society, recommends using barley straw (organic mulch) over weed membrane and shows it in use in his dahlia field.

So, to answer the question, in my experience the best mulch for dahlias in the home garden will be an organic mulch. If I have plenty of home made garden compost available, I’ll use that – keeping it topped up through the growing season. If I don’t have enough garden compost, I’ll use composted wood bark. Straw is a really good option, although it can look a bit unsightly when you use it in a mixed garden bed, which is generally where I grow my dahlias. That’s why I go for the compost/wood bark option.

Below, I’ll take you through the best organic mulches, with details of the pros and cons of each.

What is mulch and why use it for dahlias?

Mulch is any material laid upon the surface of bare soil in garden beds and containers and around the plants growing in that soil. 

Mulching your dahlias can help conserve moisture, maintain cool root temperatures, and suppress weeds. 

Importance of mulch for dahlias

Mulch plays a crucial role in the growth and health of your dahlias. By choosing the right type of mulch, you can not only improve the overall appearance of your garden but also help your plants thrive. Here are some of the key benefits of mulching dahlias.

Weed supressant

Firstly, mulch serves as an excellent weed suppressant. When applied around your dahlias, it can significantly reduce the growth of unwanted weeds by blocking sunlight and preventing weed seed germination. This ultimately helps your dahlias to grow without competition for nutrients and water, leading to healthier plants. 

Moisture conservation

In addition to weed control, mulch helps to conserve water in the soil around you dahlia tubers. When you spread mulch around your dahlias, it helps your prevent evaporation in the upper layers of the soil . This is really important for dahlias, as they do not root especially deeply and feeder roots often spread out close to the soil surface. 

Keeping the soil moist around the roots and tubers allows dahlias to establish strong root systems and prevents sudden water loss from the soil surface. Dried organic mulches like hay, grass, straw, and leaves can be particularly helpful for water retention.

Soil fertility

Organic mulches also have the ability to improve your garden soil fertility and structure over time. As it decomposes, the organic mulch material releases essential nutrients and organic matter into the soil.  

You should note that not all organic mulches provide nutrient straightaway.  Nutrient enrichment comes quite readily from those mulches that have already broken down and decomposed to a fair degree, such as garden compost.

‘Fresher’ organic mulches like wood chips, grass clippings, hay or straw need time to break down before they add nutrients to the soil. The softer the material, the quicker the breakdown happens. 

Soil temperature regulation

Mulch also acts to regulate soil temperature and works at both temerature extremes.  If you plant out your dahlia tubers early, then a thick layer of mulch can insulate them from frost. 

If you are growing dahlias in Florida, for example, or other especially hot conditions, then mulch is essential for protecting the dahlia tubers and feeder roots from excess heat.

Encourage organisms that are good for your soil

Loose organic mulch materials (and the soil beneath any kind of mulch) can provide an attractive habitat to worms, soil beetles and other micro-flora and fauna. These are important in keeping soil healthy and plant friendly.

Best types of mulch for dahlias

When it comes to mulching your dahlias, it’s essential to choose the right type of mulch to help your dahlia flowers thrive. In this section, we’ll discuss the two main types mulch you can use for dahlias: organic and inorganic mulches.

When choosing the best mulch for dahlias – much will depend on your circumstances.

For example, how you grow your dahlias is a consideration. If you grow them in and around other plants, it can be harder to apply mulch (especially sheet mulches) than if you grow them in straight beds for flower production.

You’ll also want to consider what is available to you – do you have plentiful supply of home grown compost? Do you have lots of wood chippings as a result of some tree and shrub pruning you’ve carried out? Have you got ready supplies of hay, straw, leaf mould/mulch?

The fact is – all mulch is good for dahlias. So use what is easiest for you. But I’ve set our some detail about the pros and cons of the various types of mulches below, so this will help you make your choice.

Organic mulches

Some of the best organic mulches for dahlias include:

Wood chips

A good, long lasting option, wood chips take a while to break down. Because of their relatively large size and weight, they do not compact and therefore allow water penetration. This means wood chips can be applied more thickly than other more composted mulches.

Beware very fresh woody chips of broad leaf plants as they may contain phytotoxic compounds. These are used by the plant to deter herbivores and interfere with the growth of competitor plants. It is therefore best to allow wood chips to age in a pile for 3 or 4 months before use as a mulch.

It is also best to be careful not to dig wood chips into the soil because they use nitrogen as they break down. If they are dug into the soil around your plants, they’ll take this nitrogen from the soil. This can mean reduced availability of nitrogen for your plants’ roots for up to 2 years.

Grass clippings

Grass clippings make a good quick mulch. They are usually easy to obtain (from your own lawn mowing) and easy to apply around the plants. It is better to allow them to dry out and brown a little bit before applying them around your dahlias, as they can get slimy and/or produce quite a lot of heat as they begin to decompose.

Hay and straw

Hay and straw are easy to apply mulches. Add a layer of about 6 to 8 inches at first and this will settle to about 4 inches. Hay and straw break down quite quickly, so at the end of the season you’ll have some good, well-broken down organic matter to mix in to your soil.

You should check with your supplier that your hay or straw is not affected by any residual herbicides that can leach out and damage your dahlia plants.

There is also a risk that your hay or straw mulch could be come a habitat for pests, so you’ll need to keep an eye on that. They can also be messy to apply, and not especially pleasing to the eye. But overall, hay and straw make good mulch, especially for a production situation, rather than a mixed garden bed

Wood bark

Wood bark has similar characteristics to wood chips – the difference is that the chips are made form the bark of trees rather than the woody parts. Wood bark chips will often be partially composted when you buy them in, so it is usually fine to use them around your plants straight away.

Leaf mould

Leaf mould is formed from broken down and decomposed leaves. It usually takes a year for the leaves to break down into a soft compost-like structure. Leaf mould is often used as a soil conditioner but it can work well as a mulch. It will break down further and incorporate itself into your quite soil quickly, so will require topping up regularly. It is easy to apply and easy on the eye.

Leaf mulch

Leaf mulch is really just leaf mould before the leaves have fully broken down. You can uses leaves in various stages of decomposition, but it is usually best to have allowed them to age and have bound together to some extent, or you will have ‘fly away’ mulch in dry, windy conditions.

Compost

Home made compost is probably the best mulch you can apply to your dahlias if you can get enough of it and you have the time to keep it topped up. Compost adds nutrients to the soil as it breaks down and is host to the beneficial microbes and other soil fauna that condition our soil. It is loose enough to allow water penetration, but also substantial enough to aid water retention around the plants.

The only downsides of home made compost are that it breaks down quickly and can be a bit weedy, unless produced in conditions hot enough to kills weeds seeds.

A word about peat or peat moss

You may read elsewhere that peat or peat moss is recommended as the best mulch for dahlias. I do not recommend the use of peat or peat moss for mulch, or for any purposes in the garden. 

Peat is a finite natural resource derived from ancient wetland areas and habitats. Peat bogs are also an important natural carbon storage – peatlands store a third of all the soil carbon in the world. Therefore harvesting peat destroys vital natural habitats and contributes to climate change. I wouldn’t advise you to use it as a mulch for your dahlias.

Inorganic mulches

Inorganic mulches are made from synthetic or mineral materials that do not decompose. Typical inorganic mulch materials are:

• gravel
• decorative stones
• plastic sheeting
• weed supressing fabric.

Though not as beneficial as organic mulches for dahlias, some inorganic mulches can still be used effectively.

The fabric and sheeting mulches are mostly use in commercial operations where they are spread over large areas.  They need to be removed if you want to dig or feed the soil and, in some cases, for lifting tubers.

The gravel and stone mulches can look good, but they too need to be removed or scraped away from the plants when you want to work on the soil. 

Beware of using dark inorganic materials in very warm climates as these can absorb a lot of heat and potentially damage your dahlia plants.

Factors to consider when choosing mulch

Climate

Climate plays an essential role in the effectiveness of mulch. In regions with excessive rain or humidity, it’s crucial to choose a mulch that allows proper air circulation to avoid rot or mould. Wood chips or straw work well for dahlias in such climates. On the other hand, if your area is prone to drought, opt for a mulch type that holds moisture, like compost or leaf mulch. This will help retain water and reduce the need for frequent watering.

Soil Type

Different types of soil may require different types of mulch. For sandy soils, consider using an organic mulch like wood bark, straw, or grass clippings to improve water retention and add nutrients and organic matter to the soil. Clay soils, which can retain water, benefit from mulches that enhance aeration, such as wood chips or leaf mulch. Mulching also prevents soil compaction, which is important when growing dahlias.

How to mulch your dahlias

You need to water your plants well before you mulch because one of the purposes of mulching is to keep moisture in the soil. It is therefore essential that you wait until your dahlias have established a healthy set of roots to absorb the moisture in the soil before you mulch around the plants.

Therefore, it is best to apply mulch after your dahlia plants have sprouted and reached a height of 6-8 inches. Mulching too early can potentially smother the plants or rot your dahlia tubers. 

Mulch your dahlias after you have removed all weeds around them and watered well. Generally, a layer of mulch 2-3 inches thick is the minimum requirement for dahlias. Use more where the plants may be exposed to extremes of heat and cold. Be sure to leave some space around the base of the plant, as too much mulch near the stem can lead to rotting, pests, or potential fungal diseases.

Also, make sure you refresh organic mulch from time to time as it can break down and lose its depth and effectiveness. Check the condition of your mulch regularly and replenish or replace it as needed to help your dahlias continue to thrive.

More on Growing Dahlias

You can also get much more guidance on growing dahlias in these posts:

• Taking care of dahlias: the trick with deadheading
• Dahlia pinnata: a dahlia original
• How to grow dahlias: the complete guide to dahlia care
• How to overwinter dahlia plants and tubers
• All you need to know about dahlia tubers and dahlia bulbs
• Dahlia varieties: your complete guide to all types of dahlias
• Dahlias in my garden: Six on Saturday
• Dahlia Wizard of Oz – Beautiful pink pompon dahlia
• Can you grow dahlias in raised beds?
• Do dahlias grow in Florida?
• Dahlia Wine Eyed Jill
• Dahlia Night Silence – dusky pink dahlia beauty
• Visit a dahlia farm near you
• Dahlia gall: identify and prevent leafy gall and crown gall in dahlias
• When to plant dahlia tubers
• Heat tolerant dahlia varieties: beat the heat with these 120 choice varieties