Introduction
There is nothing quite like the excitement of seeing those first few dahlia buds begin to swell in mid-summer. We all dream of those iconic Dinnerplate Dahlias that look almost too perfect to be real. Dahlias are the undisputed stars of the late-summer garden, offering a variety of colors and shapes that few other plants can match.
At Longfield Gardens, we know that every gardener looks forward to the day their dahlias finally open. It can be a bit surprising when those long-awaited flowers appear smaller than expected. If your blooms aren't reaching their full potential, it is usually a sign that the plant is looking for a little extra support from its environment.
This guide is for anyone who wants to help their dahlias grow larger, more vibrant flowers. We will cover why bloom size varies and what simple steps you can take to encourage your plants to produce the show-stopping results you desire. Small blooms are rarely a permanent problem; they are simply a signal that a few minor adjustments are needed.
Achieving impressive dahlia flowers is not about luck or complicated secrets. It is about understanding the basics of water, nutrition, and a few easy pruning techniques that allow the plant to focus its energy on size.
Understanding Variety and Natural Size Limits
Before checking your soil or reaching for the watering can, it is important to consider the type of dahlia you are growing. For a broader primer, see our All About Dahlias guide. One of the most common reasons a dahlia bloom seems "small" is simply that the plant is performing exactly as it was bred to. Dahlias come in a vast range of sizes, and each variety has a natural maximum diameter.
Know Your Dahlia Categories
The American Dahlia Society and other gardening experts categorize these flowers by their bloom size. If you planted a PomPon Dahlia or "Mignon" variety, the flowers will naturally be only 1 to 2 inches across. These petite varieties are loved for their abundance and charm, but they will never produce a 10-inch blossom regardless of how much you fertilize them.
On the other end of the spectrum are the Dinnerplate varieties. These are the giants of the garden, with varieties like 'Cafe au Lait' or 'Emory Paul' capable of reaching 8 to 12 inches in diameter. If you are growing a variety intended to be large and it is only producing 4-inch flowers, then it is time to look at environmental factors.
Setting Realistic Expectations
The size listed on a plant tag is the maximum potential under ideal conditions. For many home gardeners, a variety listed as a 10-inch flower might naturally settle at 7 or 8 inches. This is still a magnificent size for a flower. Understanding the "ceiling" for your specific variety helps you decide if your plant is actually struggling or if it is just being its natural self.
Key Takeaway: Always check the specific variety of your dahlia. Small-flowered varieties like pompons are meant to stay small, while dinnerplate varieties need specific care to reach their maximum potential size.
The Importance of Deep Watering
Water is the lifeblood of a dahlia plant. These plants are native to the high plains of Mexico and Central America, where they enjoy consistent moisture during the growing season. If a dahlia does not get enough water, its first response is to conserve energy. This often results in smaller flowers and shorter stems.
Why Surface Watering Isn't Enough
Many gardeners make the mistake of "sprinkling" their dahlias with a hose every evening. While the leaves might look wet, this surface-level moisture rarely reaches the roots. Dahlia roots typically sit 8 to 10 inches below the soil surface.
"Drainage" is a word gardeners use to describe how fast water leaves the soil. Dahlias need soil that allows water to move through it easily, but they also need that water to penetrate deep into the ground. If you only water the top inch of soil, the roots will stay near the surface where they are vulnerable to heat and drought.
Developing a Deep-Watering Routine
For the best results, you should aim for deep-watering sessions three to four times a week. Use a soaker hose or a slow-running sprinkler and let it run for at least 60 minutes. This ensures the water travels deep into the root zone.
If you are growing dahlias in pots or containers, they need even more attention. Because pots dry out much faster, they may need a deep soaking once or even twice a day during the hottest part of the summer. A dahlia that is constantly thirsty will always produce smaller, less impressive flowers.
Signs of Water Stress
If your dahlia leaves look slightly wilted in the afternoon or if the bottom leaves are turning yellow, the plant is likely thirsty. While dahlias can survive a short dry spell, they will prioritize survival over flower size. Keeping the soil consistently moist (but not soggy) is the most effective way to ensure large blooms.
What to do next:
- Check your soil moisture by sticking a finger two inches into the ground; if it feels dry, it is time to water.
- Transition from hand-sprinkling to using a soaker hose for deeper penetration.
- Mulch around the base of your plants with three inches of straw or bark to hold moisture in the soil.
- Water early in the morning to reduce evaporation and prevent fungal issues on the leaves.
Nutrient Balance and Fertilizer Choice
Dahlias are "heavy feeders," which simply means they require a lot of nutrients to build their massive stalks and flowers. However, giving them the wrong kind of food can actually lead to smaller blooms.
The Nitrogen Trap
Fertilizers are usually labeled with three numbers, such as 10-10-10. These represent Nitrogen, Phosphorus, and Potassium. Nitrogen is excellent for growing green leaves and tall stems. In the early summer, a little nitrogen is helpful to get the plant established.
However, if you continue to use a high-nitrogen fertilizer once the plant is ready to bloom, the dahlia will put all its energy into growing more leaves. This often results in a giant, lush green bush with very few—and very small—flowers. To get larger blooms, you need to switch the plant's focus from "growing" to "flowering."
Choosing the Right Fertilizer
Once your dahlias are about 12 inches tall, we recommend switching to a fertilizer that is lower in nitrogen and higher in phosphorus and potassium. Look for ratios like 5-10-10 or 10-20-20. Phosphorus is the nutrient responsible for bloom production and root health, while potassium helps with overall plant vigor and water regulation.
Apply fertilizer every three to four weeks for plants in the ground. For container-grown dahlias, you should fertilize every two weeks because nutrients wash out of pots more quickly.
The Epsom Salt Boost
A simple gardening tip for larger blooms is to use Epsom salts. Magnesium, the primary component of Epsom salts, helps the plant take up other nutrients more efficiently and aids in chlorophyll production. Adding about half a cup of Epsom salts around the base of each plant once or twice a season can result in noticeably greener foliage and more robust flowers.
Key Takeaway: For bigger flowers, stop using high-nitrogen lawn or leaf fertilizers. Switch to a bloom-boosting formula high in phosphorus once the plant reaches a foot in height.
The Art of Disbudding for Maximum Size
If you want the largest possible flowers from a dinnerplate dahlia, you must use a technique called "disbudding." This is the practice of removing some of the flower buds so the plant can focus all its energy into just one.
How a Dahlia Grows
Dahlias naturally grow their flower buds in clusters of three. There is one central "terminal" bud and two smaller "side" buds. If you leave all three buds to grow, the plant has to divide its energy and nutrients three ways. This results in three medium-sized flowers.
The Disbudding Process
To get a giant bloom, you should carefully pinch off the two side buds while they are still very small (about the size of a pea). By removing these competitors, the plant sends 100% of its flowering energy into the single remaining center bud. This is the primary method used by professional growers to achieve those massive, exhibition-sized blossoms.
When to Disbud
You don't have to disbud every branch of the plant. If you want a mix of many flowers and a few "showstoppers," you can choose to disbud only the strongest stems. This technique is most effective on large-flowered varieties. For smaller dahlia types, disbudding is usually not necessary because their charm lies in the sheer number of flowers they produce.
Action steps for disbudding:
- Identify a stem with a cluster of three buds at the tip.
- Use your thumb and forefinger to gently snap off the two buds on the sides.
- Leave the center bud to grow alone.
- Repeat this on several stems throughout the plant for a staggered display of large blooms.
Pinching and Plant Architecture
Another factor that influences bloom size is how the plant is shaped. "Pinching" is a form of pruning that encourages the dahlia to become bushier rather than growing as one single, tall stalk.
Why We Pinch
When a dahlia is between 12 and 16 inches tall, gardeners often snip off the very top of the main center stem. This signals the plant to stop growing upward and start growing outward. It stimulates the "lateral" buds (the ones in the crooks of the leaves) to grow into new branches.
The Trade-off: Quantity vs. Size
Pinching creates a much stronger, sturdier plant that is less likely to fall over in the wind. It also produces many more flowers. However, because the plant is now supporting ten branches instead of one, the individual flowers might be slightly smaller than if the plant were left to grow as a single stalk.
If your blooms are small, it might be because the plant is trying to support too many flowers at once. If you have a very bushy plant, you can prune out some of the smaller, weaker inner branches. This improves "air circulation"—how easily air moves through the foliage—and allows the plant to focus on the remaining branches, resulting in larger flowers.
Temperature and Environmental Stress
Dahlias are sun-lovers, but they do have a limit when it comes to heat. Extreme summer temperatures can actually cause dahlia blooms to shrink or become distorted.
The Heat Shut-Down
When temperatures consistently stay above 90°F, many dahlias enter a temporary state of "hibernation." To protect themselves from drying out, they may stop producing new buds or produce flowers that are half their normal size. The petals may also look "stressed" or scorched around the edges.
This is a natural survival mechanism. You cannot force a plant to grow giant flowers during a record-breaking heatwave. During these times, the best thing you can do is keep the plant hydrated and wait for the weather to cool. Once the night temperatures begin to drop in late August and September, you will often see dahlia blooms naturally double in size.
The Role of Sunlight
While heat can be an issue, a lack of sun is a more common reason for small blooms. Dahlias need at least 6 to 8 hours of direct sunlight every day. Sunlight provides the energy the plant needs to build those complex, multi-petaled flowers. If a dahlia is planted in a shady spot, it will grow tall and "leggy" (spindly) as it reaches for the light, and its flowers will be small and sparse.
Simple fixes for environmental stress:
- If a heatwave hits, increase watering to help the plant stay cool.
- Ensure no nearby trees or shrubs have grown over the summer to cast shade on your dahlia patch.
- Use mulch to keep the soil temperature down; cool roots mean a happier plant.
- Wait for the "second flush" of blooms in the cooler days of late summer for the best size.
Soil Quality and Drainage Basics
The health of your dahlia flowers begins below the ground. If the soil is too hard, too sandy, or lacks basic nutrients, the plant will struggle to grow.
Ideal Soil Conditions
Dahlias prefer soil that is rich in organic matter. Adding compost or well-rotted leaf mold to your garden bed before planting provides a slow-release source of nutrients and improves soil structure. The ideal pH for dahlias is between 6.0 and 7.0, which is slightly acidic to neutral.
If your soil is heavy clay, it can be difficult for dahlia roots to expand. Clay also tends to hold too much water, which can lead to rot. If your soil is very sandy, water and nutrients might wash away too quickly before the plant can use them. In both cases, adding organic compost is the best way to "balance" the soil.
Spacing and Competition
Dahlias also need their own space. If they are planted too close together, they will compete for the same water and nutrients. For dinnerplate varieties, try to leave about 3 feet between each plant. For smaller varieties, 2 feet is usually sufficient. Giving each plant its own "territory" ensures it doesn't have to fight its neighbors for the resources it needs to grow big flowers.
Key Takeaway: Successful dahlias need room to breathe and soil that is easy for roots to move through. Amending your soil with compost every spring is one of the easiest ways to ensure long-term bloom success.
Troubleshooting Common Growth Issues
Sometimes, despite your best efforts, your dahlias might still seem a little under the weather. Here is how to handle a few common situations that lead to small blooms.
The Plant is Green but Has No Flowers
If you have a giant, healthy-looking green bush but no flowers at all, you likely have an "over-fed" plant. Too much nitrogen and not enough phosphorus is the usual culprit. To fix this, stop all fertilizing for a few weeks, then apply a high-phosphorus "bloom booster" and some Epsom salts. Ensure the plant is getting at least 6 hours of direct sun.
Blooms are Small and Stems are Short
This is almost always a sign of water stress. If the plant doesn't have enough water to fill its cells, it cannot stretch its stems or expand its petals. Review your watering routine and make sure you are reaching those deep roots. Once the plant is consistently hydrated, the new growth will show longer stems and larger flowers.
Late Season Decline
As the season winds down in late September or October, you might notice the flowers getting smaller. This is normal. The plant is beginning to shift its energy from flower production to tuber production. The tubers are the underground storage organs that will help the plant survive the winter (or be stored by you for next year). This is a natural part of the plant's life cycle and a sign that it is preparing for dormancy.
Summary of troubleshooting steps:
- Check sunlight: Is the plant getting 6+ hours of direct sun?
- Check water: Are you watering deep enough to reach 8 inches down?
- Check fertilizer: Are you using a low-nitrogen/high-phosphorus formula?
- Check pruning: Have you tried disbudding to focus the plant's energy?
Conclusion
Growing dahlias is one of the most rewarding experiences a gardener can have. While it can be a little disappointing to see small flowers when you expected giants, remember that dahlias are incredibly resilient. Most of the time, a few changes to your watering and feeding schedule at Longfield Gardens will have your plants back on track in just a week or two.
Focus on the basics: choose the right variety for the size you want, water deeply to reach the roots, and provide plenty of phosphorus and sunlight. If you want those truly massive exhibition-style blooms, give disbudding a try—it is a simple task that yields professional-looking results.
"The secret to large dahlia blooms is simply a happy plant. When a dahlia has enough water, the right nutrients, and plenty of sunshine, it will naturally want to show off its full potential."
We invite you to explore the many different dahlia varieties available and find the ones that bring the most joy to your space. With a little patience and these simple care steps, you’ll be heading into the late summer with a garden full of the stunning, oversized blooms you’ve always wanted.
FAQ
Does pinching my dahlias make the flowers smaller?
Pinching causes the plant to branch out and produce more flowers overall. Because the plant is sharing its energy among more stems, the individual flowers may be slightly smaller than if the plant were grown as a single stalk. However, for most gardeners, the benefit of having a bushier plant with more blooms outweighs the slight decrease in individual flower size.
Why do my dinnerplate dahlias look like regular dahlias?
If your dinnerplate variety is producing small flowers, it is usually due to a lack of deep watering or improper fertilizing. It could also be that you haven't "disbudded" the plant. Without removing the side buds, the plant will produce three medium flowers instead of one giant one. Check your fertilizer to ensure it isn't too high in nitrogen, which promotes leaves over large blooms.
Can I make my dahlia blooms bigger mid-season?
Yes! You can often increase bloom size by adjusting your care routine. Start by deep-watering for 60 minutes three times a week and switching to a high-phosphorus fertilizer. You can also pinch off any small side buds on new growth. Dahlias respond quickly to improved conditions, and you will often see larger flowers on the new growth within 10 to 14 days.
Is my soil pH causing small dahlia flowers?
Dahlias prefer a slightly acidic to neutral soil (pH 6.0 to 7.0). If your soil is extremely alkaline or acidic, the plant may struggle to "unlock" the nutrients in the soil, leading to stunted growth and small flowers. Most garden soils are within a reasonable range, but if you've addressed water and fertilizer and still see issues, a simple soil test from a local extension service can provide clarity.
