How Early Topping Makes Dahlias Produce Three to Four Times More Flowers

An early, radical cut can change everything.

Anyone who loves dahlias will recognise the problem: the plants race upwards, their foliage looks impressive, yet they produce only a few flowers in the end, while the long stems topple over in the first strong gust. Garden professionals therefore use a technique that initially appears ruthless: they simply cut off healthy young shoots, often obtaining three to four times as many flowers from the same plant.

Why an early cut makes young dahlias stronger

An untreated dahlia follows its natural hierarchy. One dominant main shoot grows upwards, claims most of the plant’s energy and allows only a small number of side shoots to develop. The result is tall, leggy growth, few blooms and an unstable plant.

Early intervention changes this completely. Once a dahlia is around 20 to 30 centimetres tall and has four to five pairs of true leaves, the tip of the main shoot is removed. This small measure overturns the plant’s internal “power structure”.

Topping a young shoot early forces the dahlia to form several strong side shoots – one flowering axis becomes four to six.

Trials conducted by major horticultural institutes show that young dahlias which have been topped develop considerably more flowering stems over the season. Rather than becoming a thin pole carrying only a few large flowers, the plant branches out, stays more compact and stands more firmly.

There is one trade-off: the first flower generally opens 10 to 15 days later than on uncut plants. Over the entire season, however, home gardeners gain significantly: instead of isolated, spectacular blooms, they get a genuine cloud of flowers that is easier to cut and use in bouquets.

What happens inside the plant during so-called “topping”

The botanical explanation is straightforward. The tip of the main shoot produces the plant hormone auxin. This hormone favours the growth of the leading shoot and suppresses lateral buds. Specialists call this “apical dominance”.

When the shoot tip is removed, auxin production at that point stops abruptly. The buds at the leaf joints, previously held back, begin to grow. Instead of one stem, several robust side shoots suddenly emerge, all of which will later carry flowers.

In practical garden terms, this means more potential flower sites, weight distributed more evenly and a plant that is less likely to snap or bend. Large-flowered varieties in particular benefit noticeably, as their heavy flower heads need a stable framework for support.

The perfect timing: when dahlias should be topped

Choosing the right moment determines whether the plant benefits or suffers. Gardeners should not work to a calendar date, but to the dahlia’s stage of development.

• Plant height: around 20–30 centimetres
• Present: 4–5 pairs of fully developed true leaves
• Stem: still relatively slender, green and solid rather than hollow
• Weather: a dry day, with no rain front expected

In most areas, this stage is reached roughly three to four weeks after planting the tubers, depending on soil temperature and weather conditions. Dahlias started in containers often reach this point earlier in a warm greenhouse or on a windowsill.

How home gardeners can top dahlias step by step

The method itself is straightforward, although accuracy matters. Cutting too low unnecessarily removes plant material, while topping too late can even put the tuber at risk.

Tools and preparation

Some gardeners use only their fingers, while others prefer tools. Either approach works, provided the job is done cleanly.

• Small, sharp garden snips or nail scissors
• Disinfectant such as 70% alcohol
• Disposable gloves if necessary, to avoid transmitting disease organisms

Before each cut, briefly wipe the cutting blades with alcohol. This prevents fungal spores or bacteria from entering the fresh wound.

Making the cut

First, identify the central main shoot. Then count the fully developed pairs of leaves upwards along this shoot.

1. Find the second or third well-developed pair of leaves.
2. Position the cut directly above that leaf pair.
3. Remove the tip with a clean, straight cut.

Those with practised hands can also pinch out the tip between their thumb and forefinger. The plant will respond with a slight pause in growth over the next few days, after which new side shoots gradually become visible.

Do not cut too low: the upper leaf pairs remain as the plant’s engine, supplying energy for the new branching.

These cutting mistakes put dahlias at risk

The most common mistake is poor timing. Many home gardeners only dare to use the scissors once the dahlia already looks very vigorous. By then, it is usually too late.

As soon as the shoot reaches a diameter of around one centimetre, its interior becomes hollow. Cutting it at this stage creates something like a small chimney. Rainwater can collect in the opening, slowly travel downwards and cause the tuber to rot within a few days.

If this stage has already passed, avoid cutting and support the plant instead. A sturdy cane and a few soft ties will then save far more than a late intervention with scissors.

Other common pitfalls

• Cutting too low: If there are hardly any leaves left above the cut, the plant later lacks the “solar surface” needed for fresh growth.
• Wet weather: Cutting in the rain gives fungi an easy route in.
• Dirty tools: Bacteria can enter the vascular tissue directly through the cut surface.
• Weak plants: Dahlias that are unhealthy or weakened by slugs should first be allowed to regain strength.

When topping is worthwhile – and when it is not

Not every dahlia responds to the same extent. Large-flowered varieties for beds and borders benefit most clearly. Here, the priority is usually a dense display of colour rather than record-breaking individual flower diameter.

Anyone aiming to grow enormous individual blooms, for example for exhibitions, sometimes takes the opposite approach: side shoots are removed and only a few flowers are left, so that all the plant’s strength goes into those heads. For an ordinary home garden where cut flowers are wanted, topping young plants is clearly the more useful option.

Garden objective	Recommended technique
Many flowers for beds and bouquets	Early topping at 20–30 cm in height
Few, very large show blooms	Leave the main shoot intact and limit side shoots
Weak-growing or unhealthy plants	Stabilise first; cut very little

Care after cutting: getting the most from your dahlias

After topping, it is worth paying close attention to soil and nutrients. The plant needs energy and consistent conditions to produce many new shoots.

• Water to keep the soil lightly moist, but never waterlogged
• Apply a mulch layer of grass clippings or leaves to prevent drying out
• Feed moderately, ideally with an organic flower fertiliser
• Secure windy locations with canes or support frames

Once the new side shoots begin to form buds, particularly weak shoots can be selectively removed again. This directs more energy into the remaining, stronger stems.

Why it is worth being bold with an early cut

Many home gardeners hesitate to cut into a young plant that appears healthy and strong. The instinct is understandable: nobody wants to “damage” it. Yet those who take the step usually find the opposite happens – the dahlia later looks much more impressive, flowers for longer and falls over less often.

The technique also offers a useful opportunity to become familiar with plant physiology. You can see directly how strongly a single cut affects form, stability and flowering abundance. Anyone who has watched topped and untopped dahlias diverge so dramatically side by side will usually not want to do without this trick the following year.

Beginners may find it worthwhile to treat only some of their plants this way at first. This creates a small practical trial in the garden, more revealing than any theory – and ideally leads to a summer in which dahlia beds and flower vases are noticeably fuller than in previous years.