6 Best Fertilizers for Dahlias | How and When to Use

Native to the sun-drenched, open plains of Central America, dahlias can be found growing in either formal or wildflower gardens worldwide.  Budding in an array of colors, the regal dahlia shares its family tree with other sun-loving bloomers. Like, daisies, chrysanthemums, sunflowers, asters, and echinacea, as well as coneflower. 

Historically, indigenous cultures honored its beauty as a gift from the gods, where dahlias were used in many religious rituals and ceremonies. Today, we simply enjoy watching these multi-petaled stunners sway in the breeze from late summer all the way to the arrival of winter.

Nature does an amazing job of producing dahlias of different sizes, as well. From dwarf varieties on 8″ stems to ones the size of dinner plates on 6-foot stalks. And there’s definitely something we can do to participate in that magic. By discovering the best fertilizer for dahlias available. 

Choosing the Best Dahlia Fertilizer

Dahlia doesn’t require a lot of nitrogen, too much will give you lots of tall, green stalks covered in large leaves but very few flowers. Rather than stimulating foliage growth, dahlias crave phosphorus and potassium, in larger quantities, as this is what steers bud and blossom development.

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Fertilizer Ratio N-P-K

Dahlias flourish with the right combination of macronutrients.

Nitrogen (N) for healthy foliage, and the production of plant cells

Phosphorus (P) for robust roots and an abundance of blooms and

Potassium (K) for tuber development and resistance to disease and drought

A fertilizer designed for blooming flowers works well for dahlias, such as a 10-30-20. Its low nitrogen content will help avoid leggy stems and too much foliage growth. The high potassium and phosphorus content will support tuber development and flowering. In all cases aim to have the nitrogen level no more than 50% of the potassium and phosphorus, so a 5-10-10 for example.

Try to avoid zero nitrogen fertilizers such as 0-10-10, or at least leave them until late summer. The plant needs small amounts of nitrogen to support the production of chlorophyll which assist with photosynthesis. Plus nitrogen is required for the plant’s amino acids for new cell production and repair.

Slow Release Vs Fast Release

The second step part in your decision-making process is the application method. Do you prefer a fast-acting or a slow-release feed? Would granules, spikes, or liquid work better for you? Let’s take a closer look at each type.

Dahlias are hungry plants, that need to feed the rapid and extensive production of flowers over a full summer. Your choice of fertilizer will largely depend on two factors:

  1. Your commitment to tending to your flowers regularly
  2. The current condition of your plants

If you cannot commit the time to feed fortnightly with a fast-acting liquid fertilizer then it makes sense to switch over to a slow-release granular feed or even a fertilizer spike. Granular and spike forms also work better in wet conditions, especially if your plant is in pots. Liquid fertilizer gets washed out of potting soil with rain, whereas slow-dissolving granules are good for 4 weeks or more.

On the other hand, if you can water regularly with a liquid feed you will have a greater level of control. However, in a situation where you have a plant that needs a boost, then a fast-acting liquid fertilizer will be absorbed more quickly and have a faster impact.

Do I need to Fertilize My Dahlias?

When dahlias grow in fertile, well-cultivated soil, they don’t really need much help. However, when planted in depleted soil, dahlias respond well to extra nutrients. Just remember, avoid fertilizers with high levels of nitrogen, as this will focus all the plant’s energy on producing foliage. Leaving very little for producing flowers.

Bone Meal Fertilizers

Dahlias grow from tubers and require a robust root system to grow well. Bone meal is an exceptional source of phosphate for both tubers and bulbs. As it primarily focuses on strong root formation. Again, if your soil is already rich in nitrogen and potassium from the addition of compost or manure, supplementing bone meal alone may be the best dahlia fertilizer for you.

A handful can either be added to the hole before planting new bulbs or plants or worked into the soil around the base of established plants for slow-release nutrition.

Blood, Fish, and Bonemeal Fertilizers

Blood, fish, and bone are all rich sources of natural nitrogen and phosphate and are therefore good to have in your fertilizer store cupboard.

If your soil lacks nutrients then working any of these compounds into the soil prior to planting or around the base of established plants provides a slow release of sufficient nutrients that will attach directly to a plant’s roots, rather than sit in the soil. When watered well, vigorous root growth and healthier plants can result.

Tomato Feed

Tomato fertilizers are typically high in potassium (or potash) and this is what stimulates bud and fruit production. Since tomatoes and dahlias have similar nutritional needs, tomato feed is often, surprisingly, a good fertilizer choice for dahlias during bloom.

Fertilizers for Dahlias Reviewed 

Product testing and review research take time, effort, and money. But admittedly, I’m a huge fan of dahlias. I often snip them from my cutting garden to bring inside, when other summer flowers are past their prime.

I’ve done some extensive testing of my own in search of the absolute best fertilizer for dahlias, in the hope of making things more convenient for you.

The following reviews include consumer experiences from all across the gardening spectrum and options for different soil conditions and hardiness zones. Choosing the right product will ensure your enjoyment of these majestic bloomers in your garden, for years to come.

1. J R Peters Blossom Booster Fertilizer 10-30-20 

J R Peters Blossom Booster Fertilizer 10-30-20


  • Contains a balanced ratio of 10% nitrogen, 30% phosphorus, and 20% potassium that helps avoid leggy stem growth and promotes healthy blooms in dahlias
  • Includes micronutrients such as zinc, iron, magnesium, and manganese to ensure optimal nutrition
  • Water soluble formulation helps to speed up absorption into the soil for quick results


  • Will need to be applied monthly for optimal results

Jack’s Classic is a formula rich in phosphorus and potassium and will provide your plants with the right combination of nutrients for abundant blooms. This water-soluble dahlia fertilizer is gentle enough for use as soon as buds appear and can then be incorporated into your regular watering cycle right through the growing season.

This feed can be used as a hibiscus fertilizer as well as on vegetable plants. Flowering annuals in hanging baskets and pots also experience faster maturity, allowing for an extended bloom time.

Both gardeners and commercial growers agree that this feed not only increases the number of buds but also provides vibrantly colored blooms.

How To Use:  Use the scoop that comes with this fertilizer and mix 1 measure per gallon of water. Apply to the soil around your plants as you water every 7-10 days. 

Customer Reviews: Gardeners were amazed at how long their plants continued to bloom with this. Extending their growing season far beyond expectation. Great value for money. Making this my BEST BUY with 4.8 out of 5 stars. Click here for prices and delivery on JR Peters Bloom Booster.

2. Scotts Super Bloom Plant Food 12-55-6 

Scotts Super Bloom Plant Food 12-55-6


  • Contains 12% nitrogen, 55% phosphorus, and 6% potassium to help promote strong stem growth and healthy blooms in dahlias
  • Includes chelated iron to help stimulate chlorophyll production and increase the vibrancy of blooms
  • Water soluble formulation helps to speed up absorption into the soil for quick results


  • Lower levels of potassium may lead to underdeveloped tubers restricting overall plant size

As a familiar brand, Scotts offers this water-soluble, phosphorus-rich formula that promises instant feeding while protecting against root burn, when used as directed.

I live in an area with a short growing season, so I have to wake my dahlia tubers from winter dormancy indoors. True to their word, there was no sign of root burn even at such a tender stage in their growth. However, I did follow the instructions in the letter.

Steady growth and absence of early leaf drop and root burn carried through once I’d transferred these new plants outdoors. Scotts super bloom proved a highly effective dahlia fertilizer on new growth in early spring.

Make sure you deadhead spent flowers, as this will encourage the production of more blooms. If you don’t pinch off all the spent flowers and instead leave them on, all the plant’s energy will start to focus on seed production.  

How To Use: Pre-moisten soil prior to application. Then mix two teaspoons into each gallon of water used and water normally. Repeat every 7-14 days. 

Customer Reviews: Gardeners have tried this with a watering can, hose attachment, and backpack sprayer. All with surprising results. Even plants that were thought to bloom only once, continue to do so all season with consistent feeding. 4.6 out of 5 stars. Click here for Scotts Super Bloom Water-Soluble Plant Food.

3. Grow More Hawaiian Bud and Bloom Fertilizer 5-50-17 

Grow More Hawaiian Bud and Bloom Fertilizer


  • Effective in both harsh and temperate climates
  • Extended bloom times on single-season bloomers


  • Frequent watering & following the manufacturer’s guidelines will ensure that root burn is avoided

Formulated to encourage higher bloom production in tropicals, the primary focus of Gro-More Hawaiian Bud & Bloom is to support young plantings in becoming established. So that they produce more buds right out of the gate. 

Normally, new plantings take a while to establish as evidenced by dropping leaves and weak flower stems. I soaked the soil around each and within a few days, those leaves and stems reached out from their stalks with strength and vigor. 

How To Use: 1 Tbsp. per gallon of water after initial planting. 1 tsp. per gallon of water for continuous feeding until plants are established. 

Customer Reviews:  Dahlia growers, especially those in hot, dry climates feel that Hawaiian Bud & Bloom works like magic. Revitalized strength and color, with increased bloom production, after experiencing prolonged environmental stresses clearly demonstrated this as the best fertilizer for dahlias and other tropicals in warm climates, with great value for money.  4.7 out of 5 stars. Check prices for Gro-More Hawaiian Bud & Bloom here.

4. Miracle-Gro Bloom Booster Flower Food 10-52-10 

Miracle-Gro Bloom Booster Flower Food


  • Contains 10% nitrogen, 52% phosphorus, and 10% potassium which are all essential nutrients for strong stem growth and vibrant blooms in dahlias
  • Includes chelated iron to help stimulate chlorophyll production and enhance bloom color
  • Water soluble formulation helps to speed up absorption into the soil for fast results


  • Expensive product for a relatively small quantity of fertilizer

No complete comparison is without Miracle-Gro. This phosphorus-heavy NPK guarantees a profusion of blooms by stimulating the enzymes that trigger bountiful bud and seed production in many of my flowering annuals. Including petunias and geraniums, as well as my dahlias.

It’s worth checking the pH of your soil before you begin using this feed, though. While dahlias are served well by phosphorous, too much in the soil, compounded by added via feed, will cause root burn damage.

How To Use: In a watering can, mix 1 tablespoon of Miracle-Gro per gallon of water. Then, soak the base of your plants every 7-14 days.

Customer Reviews: Even gardeners with slow-to-bud, partial-shade bloomers responded far better than expected with Miracle-Gro. Giving their flowering plants the extra motivation they needed to produce an abundance of blooms. Highly recommended at 4.8 out of 5 stars. Click here for Miracle-Gro Bloom Booster Flower Food from Amazon.com

5. Ferti-lome Blooming & Rooting Plant Food 9-58-8 

Ferti-lome Blooming & Rooting Plant Food 9-58-8


  • Focus on robust root support for large, vibrant foliage and flowers
  • Versatile enough for ornamentals and vegetable


  • Not recommended for use on phosphorus-sensitive plants 

Ferti-Lome offers a water-soluble feeding option to care for every aspect of your dahlia’s health. From the get-go, Ferti-Lome supports root development and as plants become established you can expect larger, more vibrant blooms and lush foliage.

This feed is versatile enough to use as a general-purpose fertilizer for flowering shrubs and trees, roses, & fruiting plants. See prices for Ferti-Lome Blooming & Rooting Plant Food from Amazon.com  

How To Use: Mix 2 tablespoons into 1 gallon of water in a watering can. Repeat every 1-2 weeks during the growing season.

Customer Reviews: First-time buyers are sharing they’ll now be repeat customers after trying this product. Seeing fantastic results in everything from hanging baskets and vegetables to small border plants and large shrubs. 4.8 out of 5

6. Dr. Earth Organic Bud & Bloom Fertilizer 3-9-4 

Dr. Earth Organic Bud & Bloom Fertilizer 3-9-4


  • Organically provides an abundance of blooms
  • Versatile for use as a quick or slow-release


  • Working granules directly into the soil may raise pH levels 

Dr. Earth’s bloom booster is an organic feed that has been enhanced with seven strains of soil microbes. This help to increase and maintain soil fertility, ensuring dahlias produce a bounty of buds while supporting healthy roots and foliage as the growing season progresses.

How To Use: Apply the recommended amount per sq footage every other month throughout the growing season. Click here for Dr. Earth’s Flower Girl Bloom Booster.

Customer Reviews: Natural gardeners who are focusing on improving their soil in addition to nourishing their plants are raving about Dr. Earth’s fertilizer. Slightly increasing the pH, just the way dahlias like it. 4.7 out of 5

How to Fertilize Dahlias

A successful and effective dahlia fertilizer regimen is not complicated. Feel free to choose any one of the products I’ve tested. As they all have a low percentage of nitrogen which is what helps these regal bloomers thrive.

Wait to fertilize until you see new leaves emerge in spring. Then, continue feeding until mid-fall, following the recommended frequency on the label. Fertilizing after mid-fall is not necessary as this is when dahlias begin to die back in preparation for winter dormancy. Fertilizing in winter would only do them harm. 

Fertilizing for Maximum Flower Yield 

Dahlias will grow without the assistance of fertilizer, especially if grown in fertile soil. However, if increased blooming is your goal, fertilizing just a couple of times during the season will make a significant difference in the number of flowers you get. 

If following a more structured regimen, experts agree that a formula low in nitrogen, similar to vegetable feed, will support lushness and health throughout the entire plant. Right down to the tubers and roots.

Dahlia Soil pH 

Dahlias absorb nutrients most effectively when they’re planted in soil that has a pH of between 6.5 and 7.0. We’ve seen some fertilizing options on this list that can help increase it or you can just add a bit of lime. If your pH is too high, consistently adding compost to the soil will not only increase its fertility but lower its pH to healthy levels for your plants. 

Avoiding Fertilizer Burn 

Fertilizers can cause root burn on dahlias, or any garden plants really when nitrogen is over-applied. Specifically, by nitrogen salts. Fertilizers vary in terms of how much salt they contain. But, to avoid dahlia burn, dosage applications should always be followed if you really want to get a show-stopping result.

Over-fertilizing will not further enhance growth, flowering, or fruiting. It will only serve to decimate your plants from the inside out. 

When to Fertilize

The American Dahlia Society advises that “no fertilizer is needed to start dahlias. Usually, the root has adequate nutrients needed to start the plant. Until there are feeder roots, the fertilizer is of no value”.

Once feeder roots emerge, just below the soil surface, begin your feeding regimen with either a quick-acting liquid or a slow-release option, in the recommended frequency for each type. Continue through summer and stop around mid-fall. This will allow all growth to naturally die back before you harvest and store the tubers.

How Often to Fertilize Dahlias 

How often to fertilize will depend on the type of feed you choose. Water-soluble, liquid options will need to be applied every one to two weeks for a steady stream of nutrients. While slow-releasers may only need to be applied once or twice per season, to be released in sufficient doses with every watering. An easy-to-remember guideline would be to feed your dahlias at the same time you feed your vegetables. 

You may be interested in reading Companion Plants for Dahlias | Good and Bad

Verdict: Best Dahlia Fertilizers 

The verdict is in! The best fertilizer for dahlias is one that is lower in nitrogen compared to phosphorous and potash. The balance needs to be a combination of overall plant health combined with intricate, colorful, and plentiful blooms.

Jack’s Classic is a tried and tested formula that is recommended by gardeners and commercial growers alike. Alternatively, Scott’s Super Bloom is rich in phosphorus but gentle enough to use on dahlia tubers. Alternatively, my third choice is Grow More Hawaiian Bud and Bloom which will ensure your new plantings get established from the get-go so they produce more buds upfront.

Fertilizing Dahlias FAQs

There are some common themes that run through the questions I get asked about dahlias. Here are some of the most popular.