Introduction
There is nothing quite like the feeling of watching a dahlia bud slowly unfurl in your garden. Whether you are growing a giant "dinnerplate" variety or a delicate pompon dahlia, the anticipation of that first splash of summer color is one of the most rewarding parts of gardening. At Longfield Gardens, we know that these spectacular blooms are the highlight of the season for many home gardeners, and we are here to help you get the most out of every plant.
If you have noticed that your dinnerplate dahlias are looking a bit smaller than expected, don’t worry—this is a common puzzle with a few very simple solutions. Often, small flowers are just the plant’s way of asking for a little more water, a different snack, or a quick trim. By understanding how dahlias grow and what they need to thrive, you can easily guide them back toward producing the lush, oversized flowers you love.
This guide will walk you through the most common reasons why dahlia blooms might be undersized and provide clear, practical steps to help your garden reach its full potential. We will cover everything from variety selection and weather impacts to the secrets of professional "disbudding." With a few easy adjustments, you can look forward to a season filled with the impressive, show-stopping dahlias you’ve been dreaming of.
Understanding Variety and Genetics
Before diving into soil and water, it is helpful to start with the plant itself. One of the most common reasons a gardener might ask "why are my dahlia blooms small" is simply a matter of variety. Dahlias come in an incredible range of sizes, and each type is genetically programmed to reach a specific maximum width. For a broader primer, see our All About Dahlias guide.
If you planted a "Pompon" or a ball dahlia, the flowers are meant to be petite. These varieties usually produce perfectly round, 2-to-3-inch blooms. They are valued for their intricate petal structure and their abundance, not their individual size. On the other end of the spectrum are "Dinnerplate" dahlias, such as the famous Cafe au Lait. These are the heavy hitters that can reach 8 to 10 inches across under the right conditions.
Another standout is Thomas Edison. When evaluating your bloom size, first check the tag or the description of the variety you purchased. If the flower matches the size listed for that specific type, your plant is actually doing a great job! However, if your 'Emory Paul' (which should be huge) is only the size of a tennis ball, then it is time to look at environmental factors.
Key Takeaway: Always check the expected bloom size for your specific variety. A small bloom on a pompon dahlia is a sign of a healthy, true-to-type plant, while a small bloom on a dinnerplate variety suggests the plant needs a bit more support.
The Role of Water and Hydration
Dahlias are incredibly thirsty plants, especially once they begin to flower. A dahlia plant is made up of a high percentage of water, and it needs a consistent supply to keep its stems strong and its petals lush. When a dahlia doesn’t get enough moisture, it goes into a "survival mode."
In this state, the plant prioritizes keeping its foliage alive over producing massive flowers. One of the first signs of water stress—even before the leaves start to wilt—is a decrease in flower size and shorter stems. If the soil around your dahlias feels dry and crumbly several inches down, the plant likely lacks the hydraulic pressure needed to fully expand its blooms.
How to Water for Maximum Size
To encourage larger flowers, the goal is "deep and steady." Rather than a quick daily sprinkle, which only wets the surface of the soil, aim for a deep soak two or three times a week. This encourages the roots to grow deeper into the ground, where the soil stays cooler and moister.
- Water at the base: Keep the foliage dry to prevent powdery mildew. Use a soaker hose or a watering can pointed right at the soil.
- Morning is best: Watering early in the day allows the plant to hydrate before the afternoon heat sets in.
- Mulch is your friend: A 2-to-3-inch layer of straw, shredded bark, or compost around the base of the plant helps lock in moisture and keeps the roots cool.
Managing Summer Heat Stress
Dahlias love the sun, but they aren't always fans of extreme heat. When temperatures consistently climb above 90°F, many dahlia varieties will take a "siesta." During a heatwave, the plant loses water through its leaves faster than it can take it up through its roots. To protect itself, the plant may produce smaller flowers or even stop blooming entirely until the weather cools down.
This is a natural response, and there is no need to panic. Once the temperatures drop in late August and September, dahlias often find a "second wind" and produce their largest, most vibrant flowers of the year.
Tips for Beating the Heat
- Provide afternoon shade: If you live in a very hot climate, planting your dahlias where they get some relief from the intense afternoon sun can help maintain bloom size.
- Increase mulch: Extra mulch during a heatwave acts like insulation for the "tubers" (the underground energy storage of the dahlia).
- Patience pays off: If your blooms are small in July, keep the plants healthy and hydrated. You will likely be rewarded with much larger flowers as the autumn air turns crisp.
Fertilizing for Flowers, Not Just Leaves
What you feed your dahlias has a direct impact on how big the flowers grow. A common mistake is using a fertilizer that is too high in nitrogen. Nitrogen is great for making grass green and helping young plants grow tall, but too much of it tells the dahlia to focus all its energy on making big, green leaves.
If your dahlia bushes are five feet tall and look like lush shrubs but have tiny flowers, you might be over-feeding them nitrogen. To get bigger blooms, you want to shift the plant's focus toward phosphorus and potassium.
Understanding the Numbers
When you look at a bag of fertilizer, you will see three numbers (like 10-10-10). These represent Nitrogen (N), Phosphorus (P), and Potassium (K).
- Nitrogen (N): For green leaves.
- Phosphorus (P): For strong roots and big flowers.
- Potassium (K): For overall plant health and bloom quality.
For the biggest blooms, look for a "bloom boost" formula where the second and third numbers are higher than the first (such as 5-10-10 or 10-20-20). We recommend applying a balanced, low-nitrogen fertilizer about once a month during the growing season. Always follow the instructions on the label, as too much fertilizer can be just as stressful for the plant as too little.
What to do next:
- Check your fertilizer label for the N-P-K ratio.
- Switch to a bloom-boosting formula once the plant is about two feet tall.
- Avoid "weed and feed" lawn products near your flower beds, as these are very high in nitrogen.
- Always water the soil well before and after applying fertilizer.
The Secret of Disbudding
If you want the absolute largest flowers possible—especially for dinnerplate varieties—you may want to try a technique called "disbudding." This is a standard practice for exhibition growers, but it is easy enough for any home gardener to do. For a deeper dive into support and pruning, see How to Grow Giant Dahlias.
Naturally, a dahlia stem will produce a cluster of three buds at the very tip. There is one central bud (the terminal bud) and two side buds (lateral buds). If you leave all three to grow, the plant has to split its energy three ways. This results in three medium-sized flowers.
By removing the two side buds while they are still small (about the size of a pea), you force the plant to send all its energy, water, and nutrients into that one central flower. The result is a significantly larger, more impressive bloom on a longer, stronger stem.
How to Disbud
- Locate the cluster of three buds at the end of a branch.
- Identify the central bud, which is usually the largest.
- Carefully pinch off the two smaller buds on either side using your thumbnail or a small pair of snips.
- You can also remove the small "shoots" that emerge from the leaf axils (where the leaf meets the stem) for the next two sets of leaves down the stem. This further concentrates the plant's energy.
While this means you will have fewer total flowers on the plant at one time, the ones you do have will be much larger and better for cutting and putting in a vase.
Pinching vs. Size: Finding the Balance
Early in the season, many gardeners "pinch" their dahlias. This involves cutting off the top of the main stem when the plant is about 12 to 18 inches tall. This encourages the plant to branch out, creating a bushier shape with more stems.
While pinching is excellent for getting more flowers, it can slightly reduce the individual size of those flowers because the plant is supporting many more blooming points. If your goal is the biggest possible bloom, you might choose not to pinch your dinnerplate varieties, or you might pinch them only once and then be very aggressive with the disbudding technique mentioned above.
Key Takeaway: Pinching creates a bushy plant with a high quantity of flowers. If you prefer size over quantity, skip the early-season pinch or focus on disbudding the side branches to keep the flowers large.
Light Requirements for Large Blooms
Dahlias are sun-worshipers. To produce the energy needed for big, colorful petals, they need a minimum of six to eight hours of direct sunlight every day. If a dahlia is planted in a spot that is too shady, it will grow "leggy" (tall and thin) as it reaches for the light.
In shade, the flowers will almost always be smaller and the colors will be less vibrant. If you find your blooms are consistently small year after year in a specific spot, it might be that a nearby tree has grown and is casting too much shade. Moving the tubers to a sunnier location the following spring is often the simplest "fix" for small blooms.
Pest and Disease Impacts
Sometimes, small or distorted blooms are caused by uninvited guests in the garden. Certain insects love to snack on dahlia buds before they even have a chance to open. When these pests pierce the bud to drink the sap, they can stunt the flower's growth or cause it to open lopsided.
Common Culprits
- Thrips: These are tiny, slender insects that hide deep inside the petals. They can cause the edges of the petals to look brown and "fried," and they often prevent the flower from reaching its full size.
- Tarnished Plant Bugs: These bugs inject a toxin into the bud as they feed. This often results in "blind" buds that never open, or flowers that are small and misshapen.
- Aphids: While they usually cluster on the stems, a heavy infestation can sap enough energy from the plant to reduce bloom size.
If you suspect pests, the first step is a strong blast of water from the garden hose. This can dislodge many insects without the need for chemicals. Keeping your garden free of weeds also helps, as many of these pests hide in tall grass before moving onto your dahlias.
A Note on Aster Yellows
In rare cases, small, green, or distorted flowers can be caused by a disease called "Aster Yellows." This is spread by leafhoppers. If your dahlia flowers are small, yellowish-green, and look more like a bunch of tiny leaves than a flower, the plant may be infected. Unfortunately, there is no cure for Aster Yellows, and it is best to remove the plant to prevent it from spreading to your other dahlias.
Soil Quality and Drainage
The health of a dahlia starts underground. For the best blooms, dahlias need soil that is rich in organic matter and, most importantly, well-draining. "Well-draining" simply means that water moves through the soil easily and doesn't sit in puddles.
If the soil is too heavy (like thick clay), the roots struggle to breathe and the tubers can become stressed. Stressed roots lead to smaller flowers. You can improve your soil by mixing in compost or well-rotted manure before planting. This provides a slow-release source of nutrients and creates a "fluffier" soil texture that dahlia roots love.
Why Soil Temperature Matters
At Longfield Gardens, we always remind gardeners that timing is everything. If dahlias are planted when the soil is still cold and soggy in the spring, they can get off to a slow start. A "stunted" start in May can lead to smaller flowers in August. It is always best to wait until the soil has warmed to about 60°F before tucking your tubers into the ground. If you are not sure about your planting zone, our Hardiness Zone Map can help.
Cutting Flowers to Encourage Growth
It might feel counterintuitive, but the more you cut your dahlia flowers, the more the plant will produce. If you leave a flower on the plant until it fades and turns into a seed pod, the plant thinks its job is done. It will stop putting energy into new, big blooms and start putting energy into making seeds. For more bouquet-focused tips, see How to Grow Dahlias for Cut Flowers.
This process is called deadheading. By removing spent blooms or—even better—cutting fresh flowers for indoor bouquets, you signal to the plant that it needs to keep blooming. Regular cutting keeps the plant's "bloom hormone" active, leading to a steady supply of flowers throughout the season. For a closer look at deadheading, see Do You Cut Off Dead Dahlia Blooms?.
How to Cut for Bigger Success
When you cut a dahlia for a vase, don't just snip the flower head. Cut a long stem, going back down to just above a point where you see two new little leaves or buds starting to grow. This encourages the plant to grow even more long, strong stems for the next round of flowers.
What to do next:
- Walk through your garden every few days with a pair of snips.
- Remove any flowers that are starting to look "papery" or lose their back petals.
- Enjoy fresh bouquets! Dahlias last 5–7 days in a vase if you change the water frequently.
Realistic Expectations and Weather
Gardening is a partnership with nature, and sometimes the weather has the final say. A very smoky summer, a record-breaking heatwave, or an unusually cloudy month can all lead to smaller blooms regardless of how much you fertilize or water.
If your dahlias aren't quite reaching "dinnerplate" size this year, don't be discouraged. The beauty of gardening is that every year is a fresh start. Dahlias are incredibly resilient. Even if they have a "small" year, the tubers underground are still gathering energy. If you store them properly over the winter and replant them next year, they may produce the biggest flowers you’ve ever seen.
"The magic of dahlias is in their ability to surprise us. A plant that struggles in the heat of July can often become the star of the garden by the first week of September."
Conclusion
Seeing small blooms on your dahlias is rarely a sign of failure; it is simply a signal that the plant needs a minor adjustment in its care routine. By ensuring your dahlias have plenty of deep water, the right balance of nutrients, and a bit of strategic disbudding, you can help them reach their full, glorious potential. Remember that variety choice plays a huge role, and sometimes the best blooms are the ones that arrive with the cooler air of late summer.
At Longfield Gardens, we are committed to helping you succeed. Our high-quality tubers are a great starting point, but the love and attention you provide in your own backyard are what truly make them shine. Keep your garden a place of joy and experimentation, and the big blooms will surely follow.
- Check your variety's expected size to set a baseline.
- Prioritize deep watering and mulching to fight heat stress.
- Use a low-nitrogen, high-phosphorus fertilizer for bloom power.
- Try disbudding side buds to focus energy on one giant flower.
Ready to plan for next season? You can explore our wide selection of Big Blooms on our website to find the perfect colors and sizes for your garden.
FAQ
Why are my dinnerplate dahlias only the size of a tennis ball?
This is usually caused by a combination of high heat and a lack of "disbudding." During very hot weather, dahlias produce smaller flowers to conserve energy. To get them larger, ensure they have deep moisture and try removing the two side buds from the tip of each stem so the plant can focus all its energy on one central bloom.
Will more fertilizer make my dahlia blooms bigger?
Only if it is the right kind of fertilizer. Adding too much nitrogen will actually result in more leaves and smaller (or fewer) flowers. To increase bloom size, use a fertilizer that is higher in phosphorus and potassium (the second and third numbers on the bag), and always follow the recommended application rates to avoid stressing the plant.
Can pests make dahlia flowers stay small?
Yes, pests like thrips and tarnished plant bugs are common causes of small or misshapen flowers. They feed on the developing buds, which can stunt the petals before they even open. Regularly inspecting your plants and using a strong stream of water to wash away insects can help ensure your flowers grow to their full size.
Does the age of the plant affect the size of the flowers?
Generally, a healthy dahlia tuber will produce full-sized flowers in its first year. However, if the plant is stressed by being overcrowded or if the tubers have been divided too many times into very small pieces, the plant may be less vigorous. Providing plenty of space (at least 18-24 inches between plants) and good soil will help every plant reach its maximum potential.
