8 Best Fertilizers For Dahlias (And How To Use)

Learn all about the best fertilizers for dahlia flowers here. 

Dahlias are stunning flowers that produce hundreds of blooms through the growing season. These gorgeous flowers come in many colors, shapes and sizes and make wonderful cut flowers.  

But dahlias are heavy feeders, and if they don’t receive the right nutrients they will not produce as many blooms and the entire plant can become weak.

Today we are sharing the best fertilizers for dahlias for stronger roots and bigger blooms.

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The Best Fertilizer For Dahlias (Nutrients Needed)

The best plant food for dahlias is a low nitrogen fertilizer, often with an NPK ratio of 6-24-24 or 5-10-10. You will notice that the second two chemical numbers are often double the first number.  

This is because dahlia flowers do best with a fertilizer high in both potassium and phosphorous and low in nitrogen. This type of fertilizer is often referred to as bloom food, as it encourages the plant to produce more blooms.

Giving your dahlias the right amount of fertilizer can make a big difference in the size and amount of blooms produced.

Composted steer manure and commercial fertilizer are two common fertilizers that work well for dahlias.

Manure can be mixed into the soil at planting time, while commercial fertilizers are applied during times of active growth and bloom production.

Dahlias are heavy feeders, which means they require a rich supply of nutrients in order to thrive and produce plentiful blooms. They can boast huge beautiful blooms and produce hundreds of flowers per season. This prolific flower production uses a lot of energy: thus the need for fertilizer.

Continue reading to get our list of the 8 best fertilizers for dahlias, and how different types of fertilizers affect the plant

Learn all about the best soil for dahlias here!

Our Top 8 Dahlia Fertilizer Recommendations

Here are our top eight fertilizers that can easily be purchased on Amazon:

1. Miracle Gro Bloom Booster

Miracle Gro is a popular flower fertilizer that can work well for feeding dahlias. When used as directed it can help prevent over feeding and burning your plants with too much nitrogen. We have used the Miracle Gro bloom formula on dahlias over the years and have had good results with bloom production.

2. Dr Earth Organic Flower Fertilizer

This popular organic flower fertilizer is made from bone meal, alfalfa meal, rock phosphate and sulfates. It is a powerful natural fertilizer that will nourish the dahlia tubers and gets rave reviews from flower growers.

3. Jack’s Classic Blossom Booster

Jack’s Classic Blossom Booster has a perfect NPK ratio for dahlias: 10-30-20. This popular water soluble flower fertilizer can be used every two weeks by blending with a gallon of water and applying to plants. Make sure to read through the amazon reviews to see all the rave reviews from flower growers on this amazing fertilizer.

4. Hawaiian Bud And Bloom

Grow More Hawaiian Bud And Bloom is a phosphorous rich water soluble fertilizer that is formulated for tropical and flowering plants. This is a popular fertilizer that helps stimulate bloom production. If you already have phosphorous rich soil, however, you can skip this fertilizer as it is very phosphorous rich.

5. Scotts Super Bloom

Scott’s Super Bloom is another reputable water soluble liquid bloom fertilizer. This flower fertilizer also has a high phosphorous rate and low nitrogen, promoting prolific, full blooms. Use as directed to prevent over fertilizing or burning your plant. Many reviewers state they prefer Scott’s Super Bloom to Miracle Gro, so we plan to give this fertilizer a try.

6. Lily Miller Bulb and Bloom Food

Lily Miller Bulb and Bloom Food is a slow release fertilizer rich in phosphorous and potassium. This is a more gentle formula that can be used on any soil makeup. An amazon reviewer writes: “This is the best ever for our dahlias. Have been using it every month during the flowering season & the bees, butterflies & neighbors all enjoy the mass of flowers. Highly recommend to all my friends who are growing dahlias for the best results.”

7. Flower Fuel Bloom Booster

Flower fuel bloom booster is a very concentrated liquid feed that features high available phosphorous and potassium and very low nitrogen. This bloom booster is great if you are in a dry, drought like environment with poor soil. It will help promote large flower buds, but be careful not to overuse it.

8. Down To Earth Organic Bone Meal

This organic fertilizer provides ready to go phosphorous and calcium that will support the strong root development of your dahlia tuber. The phosphorous will assist in energy towards strong, beautiful flower blooms. Mix in with soil at time of planting.

Now that you have some ideas for different fertilizers, continue reading for more information on how different types of fertilizers work, how and when to fertilize, soil testing and overall dahlia plant health.

What Is NPK Ratio?

The NPK ratio stands for Nitrogen-Phosphorous-Potassium. These chemicals are available in fertilizers and help the plant grow and thrive. Each chemical has a different purpose:

• Nitrogen promotes healthy leaves and foliage
• Phosphoric acid is responsible for healthy root development and the production of blooms and fruit
• Potassium helps strong flower and root development + aids in the overall function of the plant

When feeding flowers, too much nitrogen and not enough phosphorous and potassium can result in more foliage and not as many blooms.

A balanced fertilizer has an equal number NPK, such as 10-10-10.  When feeding dahlias, look for a NPK ratio where Nitrogen is around half that of Potassium and Phosphorous (like 5-10-10).

Tip: The best fertilizer won’t do your dahlias won’t do any good if you are planting in poor soil! Dahlias love well draining, fertile soil and thrive in full sun. Make sure you give your plants those two basic requirements before adding dahlia fertilizer. Dahlias will not grow in cold soil, so if you plant them yearly wait until the soil has warmed to 55 degrees. Read our guide to growing dahlias here.

Benefits Of Fertilizer For Dahlias

Giving your dahlia flower the right type of fertilizer at the right time will have many benefits:

• Encourage proper growth of the plant and healthy foliage
• Increases the amount of blooms
• Helps promote stronger, better stems
• Strengthens the plant, helping prevent disease
• Encourages healthy tuberous roots, resulting in a strong plant
• The additional fertilizer can encourage larger flowers
• Stronger stems and beautiful flowers will promote a longer dahlia bouquet vase life

Learn how to deadhead dahlias for more blooms here!

Types Of Fertilizer

As mentioned above, there are many types of fertilizer to choose from when feeding dahlias.

Here we review the different types of fertilizers, what they are used for, and how to use them.  

(Do not use all of the fertilizers on this list!  First test your soil and adjust from there. A good approach is to choose a soil amendment before planting, and then either use slow release fertilizer or liquid fertilizer regularly during the bloom season.)

Steer Manure

Steer manure is an excellent low nitrogen fertilizer that can be used as a soil amendment when planting dahlias. Blend it into the soil when preparing the garden beds for dahlias.

This organic fertilizer can be purchased at most garden and farm supply stores.

Do not use chicken manure: it has a high nitrogen level and is not the best option for dahlias.

Slow-release fertilizers

A slow release fertilizer like Bulb + Bloom Food by Lily Miller will break down slowly over time in your soil. This fertilizer has an NPK of 4-10-10, featuring less nitrogen and more phosphorous and potassium.

Slow release fertilizers will release fertilizer from their granular form slowly over the course of 4 to 6 weeks. For best results apply once per month during the blooming season (July through first frost).

Liquid Fertilizer

A liquid fertilizer will deliver nutrients to a dahlia plant quickly and help the plant develop healthy tubers, stalk, foliage and flowers. 

Look for a high quality, organic liquid with a low nitrogen level, and follow the feeding instructions and schedule. This will encourage the plant to put it’s energy into growing beautiful flowers.

Liquid fertilizer should be used with care:  because of the quick uptake and availability of the fertilizer, it can burn the plants roots.  Do not overdo it with liquid fertilizers when feeding dahlias, and if you have a soil that is nutrient dense, you may opt for a fertilizer with a lower phosphorous number. 

You do not need to use both a liquid and slow release fertilizer.  Choose one or the other to avoid over fertilizing your flowers.

Bone Meal

Bone meal is an organic fertilizer that is full of phosphorous and calcium.

The best time to apply this natural fertilizer is when planting tubers: simply mix it into the soil. This encourages healthy tuber growth and strong plants, as the phosphorous feeds the tubers and helps them to develop a strong root system. 

To use, mix several tablespoons into the soil when planting dahlias. You can also work it into the soil around the perimeter of the plant.

This fertilizer can be toxic to dogs, so use caution if you have furry friends around.

Tomato Feed

A tomato food such as Lily Miller can be used to feed dahlia flowers as it has a low nitrogen content and will promote blooms. The potassium in the tomato fertilizer will stimulate blooms on both tomato plants and dahlias.

Coffee Grounds

Since they are low in nitrogen, coffee grounds can be an excellent fertilizer for dahlia plants. Their nitrogen content is around 2%.  

You can often pick up grounds for free from coffee shops.  They will increase the acidic level of soil, so take into consideration your current soil pH level and use with caution.

How+ When To Fertilize

Fertilizing dahlias should be done at two separate times:

When preparing the soil:

When preparing the soil, you can give the dahlia tuber an extra boost by adding bone meal to the soil. You can also amend the soil by adding composted steer or cow manure to the soil.

When the plants are actively growing: 

From there, fertilize dahlias during their growth and bloom season.  Follow the instructions on the back of your chosen slow release or liquid fertilizer.  Keep in mind that if you have phosphorous rich soil, you may not need to fertilize as regularly.

Soil Conditions

Dahlia flowers need well-drained soil rich in organic matter.

Sandy soil can be amended by mixing in manure and decaying organic matter such as leaves or compost.

Clay soils need to be adjusted to have better drainage. Adding in compost and decaying leaf litter can break up clay soil to make it more nutrient dense and well-draining for the dahlia garden.

No matter what kind of garden soil you have, it can usually be improved with organic matter and composted manure.  But if you already have phosphorous rich, healthy soil, then look for a fertilizer that has a lower amount of phosphorous, and skip the formulas with super high phosphorous levels. 

Get our beginner’s guide to growing flowers here.

Soil Testing

A crucial step to fertilizing dahlias is understanding your the soil quality where planting.

Knowing the chemical makeup of your own soil will help you choose which essential nutrients you need to add.

If your soil is already phosphorous and potassium rich, you may not need to use a lot of fertilizer. And if you have poor soil you will definitely want to add in composted manure and fertilizer throughout the growing season.

You can easily test your soil with a soil testing kit bought online. MySoil test kit is easy to use and has accurate results. From here you can do proper soil preparation specific to the chemical makeup of your soil.

There are hundreds of beautiful dahlia varieties…read about our favorite dinner plate dahlia here.

Signs You Need to Feed Dahlias

If your dahlias need more fertilizer, they will let you know with a few tell-tale signs:

• Your plant may produce less blooms, or not produce blooms at all
• Dahlia plant growth may be stunted
• Unfed plants may have weak stems and not produce as many branches

Negative Effects Of Too Much Fertilizer

Can you over fertilize dahlia flowers?  YES!  Too much fertilizer can cause yellowing leaves, weakened stems and an overall decline of plant health.

The best approach to fertilizing dahlias is to amend the soil when planting, then fertilize once per month during the bloom season, or according to your soil quality and fertilizer instructions. 

And if you have healthy, rich soil, then go easy on the soil amendment and fertilizers.

Overall Plant Health + Care

Dahlias are fairly easy to grow but crave warmth + sunlight: they will not thrive until all danger of frost has passed.

In addition to fertilizer, you can keep your dahlia plants healthy by giving them at least 6-8 hours of direct sunlight. Morning sunlight that fades to shade in late afternoon will provide a perfect growth environment for your flowers.

Dahlias appreciate moist, well draining soil. Plan for deep watering at least once a week during mild weather and water more frequently as hot weather increases during late summer. (Hot, dry climates will need more frequent watering).

Because of their large flower heads, many dahlias need support by staking with flower stakes or tomato cages.

Learn more about caring for dahlias in our ultimate guide to dahlia care here.

How To Increase Dahlia Blooms

Fertilizing your dahlia plant is just one way of ensuring generous blooms.  These tips will also increase flower production:

• Make sure to plant your dahlia in full sun!  Shaded dahlias will have weak stems and create leggy plants as the stems are forced to reach after sunlight.
• Pinch out the center stalk of the dahlia plant when it is just a few inches tall. This will cause the plant to branch out and create a bushier, fuller plant with more blooms. 
• Prune old blooms right away in order to see new growth. The plant will branch out and create even more flowers when pruned properly.  (Learn how to prune dahlias here).

Resources

For further reading visit the American Dahlia Society or Swan Island Dahlias.

FAQ

Summary

When fertilizing dahlias, seek out fertilizer with low nitrogen and higher amounts of phosphorous and potassium. 

Manure and commercial slow release fertilizers are both popular options. 

I recommend blending composted manure into the soil before planting, then feeding your dahlias once a month during blooming season with a highly rated fertilizer.  

There are many flower fertilizers to choose from and I’ve enjoyed Miracle Gro bloom formula with good success.  

Giving your dahlias the recommended amount of the right kind of fertilizer will allow for vigorous growth and lots of blooms. You’ll be swimming in lush bouquets of healthy dahlia flowers all summer!

Treating your plants to a little extra love and care will ensure your plant is healthy and produces flowers all summer long!