Dahlias, the vibrant tuberous perennials often grown as annuals in cooler climates, are beloved for their spectacular, late-season blooms. While they will grow on their own, a simple horticultural practice known as pinching back is instrumental for maximizing flower production and developing a strong, well-structured plant. This technique encourages a more robust habit, transforming a potentially lanky stem into a sturdy, multi-branching specimen. The reward for this small effort is a continuous flush of impressive color lasting until the first frost.
The Purpose of Pinching Back
Pinching back a dahlia directly manipulates the plant’s natural growth pattern by overcoming a biological phenomenon called apical dominance. The primary, central stem produces a hormone that suppresses the growth of lateral buds lower down the stalk. Removing the terminal bud—the soft, new growth at the very top—eliminates this source of growth-inhibiting hormone.
This removal redirects the plant’s energy, stimulating the dormant side buds to develop into new, lateral branches. Instead of one main stem, the plant is encouraged to produce two or more new shoots from the nodes below the cut. This process results in a bushier plant structure and significantly increases the number of potential flowering points. Although the initial flowering may be delayed by a week or two, the overall bloom count for the season will be much higher.
Optimal Timing for the Initial Pinch
Timing the initial pinch correctly is important for success, as it ensures the plant is mature enough to recover and respond effectively. The dahlia should be well-established and actively growing, having passed all danger of frost in the garden. For most tall-growing varieties, the plant should reach a height of approximately 10 to 16 inches before this step is taken.
The primary indicator of readiness is the development of true leaf sets on the main stem. Growers generally recommend pinching when the plant has developed at least three to four sets of true leaves. Counting the pairs of leaves from the soil upward helps ensure the plant has enough stored energy and nodes remaining to initiate vigorous new side growth. Performing the pinch too early can stress a young plant, while waiting too long may result in a tall, unstable plant.
Step-by-Step Pinching Technique
The physical execution of the pinch, sometimes called “stopping,” should be deliberate and precise to promote clean healing and rapid new growth. Identify the main central stem and locate the third or fourth set of true leaves counting up from the ground. The cut should be made just above the desired leaf set, which is the point where the new side shoots will emerge.
Remove the entire growing tip, including the top set of leaves and the terminal bud. This section of growth is typically soft and can often be cleanly removed using just the thumb and forefinger, hence the term “pinching.” Alternatively, using clean, sharp snips or bypass pruners is advisable to ensure a sterile cut that minimizes the risk of crushing the stem tissue.
Post-Pinch Care and Ongoing Maintenance
Immediately after the initial pinch, the plant requires consistent attention to support its new, multi-stemmed structure. Since the plant will grow wider and heavier, support is a necessity for all but the shortest varieties. Staking should be implemented early, preferably when the plant is first put in the ground, or immediately after the pinch. Use sturdy wooden or metal stakes to prevent wind damage or collapse under the weight of the future blooms.
The surge of new, vigorous growth increases the plant’s demand for nutrients and water. Dahlias are heavy feeders, and a balanced fertilizer low in nitrogen should be applied regularly to support stem development and subsequent flowering.
As the season progresses, ongoing maintenance involves deadheading, which is the removal of spent flowers. Removing faded blooms stimulates the plant to continue producing new flower buds rather than diverting energy into seed production, ensuring a continuous display until the season concludes.