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 different sizes of dahlias, as well. From dwarf dahlias on 8 inch 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

These blooming beauties don’t require a lot of nitrogen. In fact, too much nitrogen will give you lots of tall, green stalks covered in large leaves but very few flowers. Rather than stimulating foliage growth, dahlia’s need phosphorus and potassium in larger quantities as this is what steers bud and blossom formation.

For this reason, you’ll want to choose a fertilizer that gives your dahlias just the right amount of each nutrient for an overall healthy, robust plant with plenty of blooms.

The other part of your decision-making when choosing the best fertilizers for dahlias 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.

Granular Vs Liquid Fertilizer 

The difference between granular and liquid fertilizer is simply a matter of what works best for you, in terms of its ease of use and your end-result expectations. Liquid fertilizers are quickly carried to the roots, allowing for immediate uptake. They can keep pH levels balanced, too. But, caution is recommended, as over-feeding could lead to root burn.

Concentrated granules on the other hand are slow-releasing and provide a consistent flow of nutrients for several months at a time, saving you time and effort. These typically need sprinkling over the soil around your plants and lightly digging in.

Once the granules become wet – either from the rain or being watered by you – they become activated and start to get to work by breaking down and becoming absorbed into the soil and then by the roots of your dahlias.

Liquid Concentrate or Spray 

A water-diluted mixture of concentrated nutrients can work through either quick root absorption when applied directly to the soil around your plants or as a foliar spray. This can be a longer-lasting, cost-effective choice. A little liquid concentrate can go a long way and can be securely stored on your potting shelf, with no mess, until you’re ready to use it.  

Dahlia Fertilizer Granules or Powder 

Granules are a time-saving, slow-release option. Heavily concentrated, they provide consistent nourishment for up to nine months. Releasing nutrients with every watering.

Powder fertilizers can be worked directly into the soil as a slow-release method or diluted in water as a “tea” for faster absorption. While powders are some of the most economical, they do carry a risk of root burn if exact measurements are not followed. 

Fertilizer Spikes for Dahlias 

Spikes are one of the easiest application types to use, especially if you have lots of these bloomers. They are pre-measured, compact, and slow-releasing with little risk of root burn.

Watering them in is not necessary either, as nutrients are released from the spike by micro-organisms that naturally live in the soil. Fertilizer spikes formulated for tomatoes are perfect to use on dahlias as they have very similar nutritional needs. 

Dahlia Fertilizer Ratio N-P-K

Dahlias flourish with the right combination of macronutrients. Nitrogen (N) – for healthy foliage, phosphorus (P) – for robust roots and an abundance of blooms and potassium (K) – for durable resistance to disease.

Producing such complex flowers takes energy, especially the large ones. So, a 5-10-10  or 10-20-20 NPK is recommended. If you use compost in your soil, you could even get away with a 0-0-10.

PRO-TIP

Fertilizer labels display a three numbered ratio, known as an N-P-K. Indicating its proportions of nitrogen, phosphorus, and potassium. Example: 5-10-5 means 5% nitrogen, 10% phosphorus and 5% potassium.

Do I need to Fertilize My Dahlias? 

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

A lower proportion of nitrogen in the NPK will still produce healthy foliage. Yet, with plenty of scope for flower production. 

Is Bone Meal Good for Dahlias 

Dahlias grow from tubers and require a robust root system to grow well. Bone meal is an exceptional, organic choice as a phosphorus source for both tubers and bulbs. As it primarily focuses on strong root formation. 

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. 

Is Blood Fish and Bone Good for Dahlias 

Fish-based compounds are another solid tool in a gardener’s organic fertilizer collection. Blood, fish, and bone are all rich sources of natural nitrogen and phosphate.

Working this 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 result. 

Is Tomato feed good for Dahlias 

Tomato fertilizers are typically high in potassium (or potash) and this is what stimulates bud production and thus, a lot of tomatoes. Since tomatoes and dahlias have similar nutritional needs, tomato feed will encourage far more buds on your dahlias than without.

Dahlias that produce flowers that grow to 8 inches across, particularly benefit from this.  


Best Fertilizers for Dahlias Reviewed 

Product testing and review research takes time, effort, and money. But lucky me, I’m a huge fan of dahlias since I use them as cut flowers when summer flowers are past their best.

For your convenience, I’ve done some extensive testing of my own. Including consumer experiences from all across the gardening spectrum. Below are my picks for the top 6 best fertilizers for dahlias. Choosing the right product for you will ensure your get to enjoy these majestic bloomers in your garden.


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

J R Peters Blossom Booster Fertilizer 10-30-20

Jack’s Classic is a formula rich in phosphorus and potassium and will provide your dahlia plants with the right combination of nutrients for abundant blooms. This water-soluble fertilizer is gentle enough for use as soon as buds begin to 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 being suitable to use on vegetable plants and in hanging baskets and pots and containers for a broad range of flowering annuals.

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.

Pros      

  • Quick dilution for use with watering cans or hose attachments
  • Extends bloom time beyond expectation

Cons

  • Not recommended for plants growing in compost-enhanced soil 

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

Scotts Super Bloom Plant Food 12-55-6

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 start my dahlia tubers indoors. True to their word, there was no sign of root burn even at such a tender stage in the growth of my dahlias. However, I did follow the instructions to the letter.

This steady growth and absence of early leaf drop and root burn carried through once I’d planted outdoors as Scotts super bloom proved highly effective 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.

Pros      

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

Cons

  • Frequent waterings & floowing manufacturer’s guidelines will ensure that root burn is avoided

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

Grow More Hawaiian Bud and Bloom Fertilizer

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 evident 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. Both dahlias and tropicals, under environmental stresses, resumed strength and color with increased bloom production. With great value for money.  4.7 out of 5 stars. Check prices for Gro-More Hawaiian Bud & Bloom here.

Pros      

  • Increases rate of establishment for new plantings
  • Higher phosphorus content for more flowers 

Cons

  • Not recommended for use in phosphorus-rich soil  is avoided

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

Miracle-Gro Bloom Booster Flower Food

No complete comparison is without Miracle-Gro. The phosphorus-heavy NPK guarantees a profusion of blooms by stimulating 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. While dahlias are served well by phosphorous, too much in soil and then more added via feed will cause damage such as root burn.

How To Use: In a watering can mix 1 tablespoon of Miracle-Gro per one 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

Pros      

  • Plentiful flowers in just a few days
  • Easy to use and store

Cons

  • Multiple boxes may be needed for larger gardens 

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

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

Ferti-Lome offers a water-soluble feeding option to care for the overall plant health of dahlias. From the get-go, Ferti-Lome will support 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

Pros      

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

Cons

  • Not recommended for use on phosphorus-sensitive plants 

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

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

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

How To Use: Apply the recommended amount 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

Pros      

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

Cons

  • Working granules directly into soil may raise pH levels 

How to Fertilize Dahlias Step-by-Step 

A successful and effective fertilizing regimen for your dahlias is not complicated. Feel free to choose any one of the products I’ve tested. As they all have a low ratio 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 according to 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 Dahlias 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 in my testing that can help increase it or you can 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 Dahlia Fertilizer Burn 

Fertilizer can cause root burn to dahlias, or any garden plants really result from the over-application of nitrogen. Specifically, 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 Dahlias 

For healthy growth throughout the season, begin feeding when new sprouts begin to emerge from their tubers, in spring. Then, continue with either a quick-acting liquid or a slow-release option, in the recommended frequency for each type. From the beginning of summer until mid-fall. Feeding dormant dahlias in winter is not necessary. 

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. 

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 luscious, 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 phospherous rich but gentle enough to use on dahlia tubers. Alternatively, my third choice is Grow More Hawaiian Bud and Bloom that will ensure your new plantings get established from the get-go so they produce more buds upfront.

Fertilizing Dahlias FAQ’s

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