Updated at: 24-05-2022 - By: Sienna Lewis

The cultivation of dahlias is not difficult at all. They’re easy to grow and provide months of large, vibrant blooms. Here’s everything you need to know to get the greatest results, from planting tubers to pinching, staking, and harvesting.

1. Know Your Tubers

During the fall, dahlia buds begin to form. Above the tubers on the stalk are these bud-like projections. Food storage tubers, which are not the source of the plant’s sprouts, aid in the plant’s early development by providing nutrients.

How To Fertilize Dahlias In 3 Easy Steps - Krostrade

As single tubers with a bud attached or in a clump of tubers around a stem, Dahlias can be obtained.

2. Timing is Key

Wait until the soil temperature reaches 60 degrees Fahrenheit before planting tubers. In cold soil, dahlias will not thrive, and their leaves are extremely vulnerable to frost damage.

A few weeks before the final predicted frost date, dahlias can be started indoors. Moisten the growing mix in a 1 or 2 gallon pot. Make sure that the stem or sprouts are facing up when you plant the tuber(s). Water sparingly and keep the pots in a warm, well-lit location. Start watering your plants on a regular basis as soon as they’ve grown several inches tall. The risk of frost has gone, therefore it is safe to move the transplants outside.

3. Know Where and How to Plant

Full sun and good, well-drained soil are the optimum conditions for Dahlias to thrive. Dahlias for the border can be planted 15 inches apart, while those for the ordinary bed should be 18 inches apart.

12″ of soil should be loosened. Mix in equal parts compost and all-purpose granular fertilizer to the planting area. To plant the tubers, make a hole in the ground and hold the stems or sprouts erect. No more than 1-2 inches of soil should be positioned beneath the top of the tubers, where the sprouts arise. Soil should be used to re-fill the gap.

4. The Value of Pinching and Staking

Pinch off the main stem when the plants reach a height of 12 inches. More stems and blooms will arise as a result of this encouraging lateral branching. See HERE for instructions.

There are two types of dahlias: border dahlias and full-size dahlias, which are both self-sustaining. Options for staking can be found HERE.

5. Watering and Fertilizing

Dahlias thrive under conditions of regular watering. When using drip irrigation, water is routed directly to the roots, keeping the leaves dry. Once or twice a week is the ideal frequency for hand-watering. Help keep the roots of your plants cool and moist with a layer of mulch around them.

Dahlias are fertilized in a variety of ways. They’ve been dubbed “heavy feeders” by others. Others argue that fertilizing is unnecessary. Dahlias thrive in rich, organic soil that is rich in organic materials, according to most gardeners. Rotted manure or compost should be spread over the area and buried 12 inches deep before planting each spring.

The usual rule of thumb is to treat dahlias like a tomato plant and water them regularly. Feed your plants once or twice a month with a low-nitrogen liquid fertilizer once they’ve started blooming with an all-purpose 5-5-5 fertilizer. Stop fertilizing by early September if you intend to store the tubers.

6. Controlling Insects and Disease

Avoid the use of chemical pesticides and herbicides to protect pollinators including bees, butterflies, and other insects.

Dahlia leaf should be kept as dry as possible to reduce the risk of disease. Allow the top inch of the soil to dry out between waterings. The bottom 12″ of leaves should be cut back to allow for better air flow.

Dahlia leaf is a favorite food for slugs and snails. When applied early and renewed frequently, Sluggo Plus is an excellent organic pest control. Pollinators aren’t at risk because it’s sprayed on the soil’s surface. Earwigs, a common pest of dahlias, are also a problem. Bugs like to live in chilly, wet circumstances and can wreak havoc on plant growth. Keep the area around your dahlias free of dead flowers and foliage to minimize their impact. Earwigs will have fewer locations to hide and breed if you don’t use leaves or straw as mulch.

Ultimate Guide to Growing Dahlias for Beginners - Petal Republic

7. Be Generous

Dahlias are among of the best cut flowers in the world, and a few stems are all you need to put together a stunning bouquet. Flowers are healthy for the plants and encourage them to keep blooming month after month by removing them from the ground. Make frequent cuts and distribute widely! Dahlias are a wonderful gift for family, friends, neighbors, and workplace.

8. Deadhead Regularly

Maintaining a tidy landscape by removing flowers that are past their prime fosters the growth of new buds, as well as the prevention of pests and disease. Nip off the flower heads when you’re short on time. Otherwise, trim the wasted blossoms back to the main stem using scissors or pruning shears. You’ll be able to foster longer stems that are better suited for cutting by doing this.

Nutrients for Dahlias

What are dahlias taking from our soil that we aren’t replenishing? I asked several growers this question over the years as the root yield and keeping qualities of the dahlias deteriorated. Adding trace elements year after year was a common practice among farmers, but it didn’t seem to be advantageous in our environment.

Six years ago, the dahlias appeared to be developing slowly in early July before a strong rainstorm with plenty of lightning and rain hit them. [circa 2006] First, I bought urea (46 percent nitrogen) to experiment with applying nitrogen to the ground to a dahlia row (urea is very watersoluble). Then, I noticed that the dahlias had grown significantly within one week. A week after applying N., I noticed no burning of the leaves, so I continued to apply it in larger doses.

Dan Franklin (Heartland Dahlias) suggested an experiment this year because we have a large area of land that has been unused for decades. Soil tests conducted before to the experiment yielded a reading of 82 ppm (Bray P1 test – extremely high range). It measures the soil’s accessible phosphorus (P), K (mid range), Mg (high), and calcium (1200 ppm) concentrations, with results of pH 7.7 and CEC 7.4. The soil is a sandy loam, and the garden receives about 5 hours of direct sunlight each day, with the remaining coming in through the trees on the east and west sides of the property.

All of Dan’s roots (M FD R) had sprouts about 2–3 inches long when the dirt was tilled. Since Dan like to grow dahlias in small pots, we placed two potted roots and eight bare roots in each area. Two roots were planted per spike and the space was divided into four equal groups on May 20. The stakes were 30 inches apart and the groups were 5 feet apart. Each group’s soil preparation is listed below.

A pound and a half Magnesium, lime, and half a cup of captan. Approximately 45 square feet of this material was distributed, and the top 2 to 3 inches of soil were worked in. In other words, the groundwork had been done.

There are two pounds in Group 2 Worked into the soil was a mixture of 20-5-10 and 1/4 pounds of sulfur. The stakes are in the ground, and the roots are beginning to grow.

Groups #3 and #4. Stakes and roots were already in place, so there was no need to do anything further.

Groups #3 and #4 on June 1st, 2019. These two sets of sprouts are beginning to break through the surface. One tablespoon per gallon of Urea was applied to the earth around each plant in each group (about 1 gallon to each plant).

Groups #3 and #4. Apply 1 heaping tablespoons to each plant (8 – 10 inch radius) and leave this on the surface rather than working it into the soil.

This is the third and last group. Each plant received a 60 percent dose of K.

9th of June, Group #3 & 4. In each group, I applied 1/4 to 1/3 pound of sulfur and stirred it into the soil to reduce the pH.

A heaping tablespoon of N was sprayed every three weeks to groups #3 and #4 from June 5 through August 20 and left on the soil or mulch to be soaked in.

Groups #1 and #2 received no additional fertilizer during the growing season.

On June 1, I noticed that in groups #3 and #4, all of the roots had sprouted, with all 10 roots sprouting in each group. After 10 days, Group #1’s roots started sprouting, and all ten of them sprouted. Only four of the ten roots in group #2 developed, one week after the first group.

The tops of all plants had around four sets of leaves and there was no disbranching. After the first set of leaves have fallen, plants are fastened to a stake, disbudded, and any secondary branches are cut off.

Irrigation and mulch were applied to the plants.

On or around July 15th, groups #3 & #4 blossomed, on or around July 22nd, on or around August 5th, on or around

At the end of the season, the height and number of plants (including the two dahlias of each group cultivated in pots) of each group

10-out-of-ten in Group#1: 4 ft, 3 1/4″

A total of 4 of 10 in Group #2, measuring three feet and one quarter inches.

Group 3 – 5 14 feet – 3 5/8 inches – 10 out of 10;

Groups #3 and #4 had substantially darker green foliage, with the addition of potash making group #3 even darker. Both groups of plants had more branch growth, which resulted in more blooms and longer stems, but the total percentage of bloom/stem/foliage was acceptable.

All groups had good bloom position, and the stems were never weak, mushy, or rubbery over the growing season; the blooms were always retained upright with good bloom position. In spite of the fact that there was a noticeable difference in the size of the flowers, I was unable to determine the form, substance or quantity of ray florets in any of the blooms.

Observations from experiment and some of my recommendations for dahlia growers getting started:

To determine the amount of nutrients in the soil, a soil test is required.

Dahlias don’t need fertilizer to get started because the roots typically contain all of the nutrients needed to get the plant off the ground, and fertilizer is useless until feeder roots appear. I think the fertilizer applied before to planting inhibited growth in group #1 and burned roots in group #2, as evidenced in the two groups with fertilizer in the soil around the roots.

Dahlias do not necessitate a large amount of P to thrive (over 100 ppm). There are no movement or leaching of phosphorus after application. papers and websites I’ve consulted have informed me that excessive amounts of P may induce potassium depletion and perhaps hinder the consumption of other nutrients (but these articles do not state the level of P to cause this condition).

For its first few years, dahlias don’t require a lot of water to thrive. Dahlias thrive in moist and warm soil, although wet soil might lead to rot. Dahlias can be started in the ground or in a greenhouse.

To conserve water and keep the soil evenly moist, mulch around the dahlias. When it doesn’t rain, once a week is generally sufficient for our sandy soil. There may be a variety of insects and pests hiding in mulch in various regions, so prevention is a requirement.

How to Start Dahlias Early - Justagric

Perhaps less nitrogen is needed in clay soils because the clay particles are better at retaining nutrients (nitrogen and potash) than in lighter soils.

A phosphorus test conducted four years ago found the soil in the dahlia garden to have more than 750 parts per million, and no phosphorus has been added since. A reduction of 430 pounds per acre or 230 parts per million in phosphorus concentration has occurred over this time period. For the dahlias we have in our garden, this means they need 110 pounds of phosphorus per acre each year, or roughly 25 pounds for 10,000 square feet, and I was applying 2 to 3 times this amount each year.

As a test, I’m going to dig some roots from each group and store them individually. Next spring, I’ll let you know.

Next year, I aim to utilize larger cultivars, repeating the fertilizer application and keeping the sections isolated, because some growers will criticize my usage of nitrogen on these plants.

How To Fertilize Dahlias Correctly

When it comes to fertilizing dahlias, it’s important to keep in mind that the soil itself is typically the most important consideration. As a side note, it’s important to note that new plants don’t need fertilizer because they don’t yet have feeder roots. Because overwatering causes rot, you don’t need to provide water to dahlias when they’re just starting out in the ground or in the greenhouse.

Know the best fertilizer

Soil testing is the best way to determine what fertilizer your dahlias need, according to the American Dahlia Society. Because you have the ability to alter the dahlias’ environment, growing them in a greenhouse may be advantageous. You can choose the fertilizer to apply after checking the pH and composition of the soil.

All year long, you can feed your dahlias with a high-nitrogen fertilizer, but be sure to reduce it towards the conclusion of the season. When applied in moderation, nitrogen promotes bush development and large blooms, while excessive amounts might result in poor growth and poor-quality tubers. In order to assist dahlias grow strong and develop their roots more quickly, potassium is more important.

For dahlias, Oregon State University advises 5 pounds of a 0-20-20 fertilizer for every 100 square feet. Monitoring nitrogen levels and focusing on potassium and phosphorus are critical to the success of a plant. There are formulas where the first number is lower than the last if you’re a novice gardener.

When to fertilize

Before planting, manure or compost can be added to the soil, according to the University of Vermont Extension. It’s thus possible to apply a quarter-pound of balanced fertilizer for every ten square feet of land after a month, Feeding dahlias 30 days after planting promotes the tubers to generate sprouts and stems, which is why it is beneficial.

Every four weeks from mid-summer through autumn is a good time to apply fertilizer to your plants. This will allow dahlias to grow stronger roots and produce more flowers. In order to ensure that your Dahlias thrive, follow these feeding schedules.

How to fertilize

Prior to planting your dahlias, you must choose how much fertilizer to use. To avoid overfeeding or underfeeding, check the label on the fertilizer to see how much is needed per square foot. A 2-foot ring of fertilizer can be created by placing half a cup of fertilizer around your plants and working it into the soil.

Make sure to moisten it up to aid in absorption and prevent burning of the roots while you’re just getting started. When it comes to dahlias, some gardeners claim that they don’t need to be fed at all. To get a sense of your plant’s feeding requirements, it’s best to check the soil first.

Dahlias can be fertilized in the same way that tomatoes are, something you’ve probably heard before. Dahlias can be planted using an all-purpose fertilizer and then fertilized with a low nitrogen liquid fertilizer once a month once they begin flowering, according to this rule. Make sure to cease fertilizing early in September if you plan to use tubers in the future.

Additionally, if you fertilize with a high-phosphorus feed every three weeks in the early summer, you can encourage stronger aerial development. When the dahlias fall back in late summer, you can stop feeding because the plants will soon be dormant in the winter. By the end of the season, you want to discourage dahlias from growing foliage so that they have enough nutrients in their tubers.


A greenhouse is a great way to guarantee healthy growth and blooming of flowering plants like dahlias, no matter where you live. A lot of their success is up to you, including knowing the right method of fertilizing dahlias. First, identify the best fertilizer, the suitable time of year, and the proper method of fertilization of dahlias.

One gardener may claim that dahlias are arduous feeders, while another claims that they are a breeze to care for. There are a lot of conflicting advice on how to fertilize dahlias from different gardeners. To keep from becoming overwhelmed, keep in mind that your soil is the most important consideration and that fertilization is pointless until feeder roots have formed.

Because of this, it is important to examine the condition of your soil before adjusting the feeding. You can also start by fertilizing dahlias like you would tomato plants.