The annual herb Anethum graveolens, commonly known as dill, is popular in cooking for its feathery foliage and aromatic seeds. When gardeners ask, “Does dill spread?” the answer is definitively yes, though not through aggressive root systems like many perennial herbs. Dill spreads primarily by self-seeding, which results in new, unplanted “volunteer” plants appearing in the garden beds and surrounding areas year after year.
Seed Dispersal and Self-Sowing
The mechanism for dill’s spread is its prolific seed production and subsequent dispersal, a characteristic common to the Apiaceae or carrot family. A single mature dill plant produces numerous umbrella-like flower heads, called umbels, which are densely packed with small, light brown seeds. These seeds are technically schizocarps, which are dry fruits that split into two seed-like halves when mature.
If the plant is left unharvested, the umbels dry out and naturally shatter, releasing the seeds onto the soil below. Dill seeds are lightweight and can be easily moved beyond the planting site by wind, flowing water, or by being tracked on garden tools and animal paws. This natural distribution leads to volunteer dill plants appearing in unexpected locations the following growing season.
The seeds remain viable for several years under good conditions, allowing successive generations of plants to emerge from the initial planting. This self-sowing habit means that even if the original annual plant dies back, its offspring will appear in spring, making it behave much like a returning perennial. Because a single plant can produce hundreds of seeds, the potential for widespread volunteer plants is substantial if the process is left unmanaged.
Understanding the Root Structure
Dill’s physical structure clarifies why its spread is limited to self-seeding above ground, rather than underground. The plant develops a single, deep taproot, much like a carrot or parsnip, which are related species. This taproot can grow quite long, sometimes reaching depths that make the plant difficult to transplant successfully once established.
The presence of this non-branching, central taproot confirms that the individual dill plant remains stationary in its location. Unlike many perennial herbs such as mint, which utilize underground runners or rhizomes to colonize new territory, dill does not invade neighboring space by sending out lateral root structures. The root system is designed for vertical anchoring and nutrient absorption, not for horizontal vegetative propagation.
Controlling Volunteer Plants
For gardeners who wish to enjoy dill without it taking over the entire garden, managing the self-sowing process is straightforward and focuses on intervention before the seeds drop. The most effective method is “deadheading,” which involves removing the flower heads before they have fully dried and released their seeds. Cutting the umbels when they are still green or just beginning to turn light brown prevents the natural shattering that disperses the seeds.
Strategic harvesting can also be used to control the spread while still yielding a crop. By cutting the entire plant down for seed harvest when the umbels are golden-brown, the gardener collects the seeds in a controlled manner, typically into a paper bag, instead of allowing them to fall to the soil. This simple action removes the potential for hundreds of seeds to become new volunteers.
Additional Control Methods
Gardeners can use several techniques to minimize unwanted dill:
- Utilize succession planting, sowing small batches of seeds every few weeks and removing the plants before they have a chance to flower and set seed.
- Hand-pull or shallowly till volunteer seedlings in the spring while they are small, as their delicate taproots are easily disrupted.
- Apply a thick layer of mulch to suppress the germination of any seeds that have fallen to the soil.