Tomatillos, often called husk tomatoes, are a unique fruit belonging to the nightshade family and encased in a distinctive papery husk. The answer to the most common question about growing them is straightforward: yes, you generally need at least two tomatillo plants to ensure successful fruiting. Planting a single tomatillo plant typically results in lush foliage and numerous flowers, but very few, if any, actual fruits. This necessity stems from a reproductive mechanism that prevents the plant from fertilizing itself.
The Biological Necessity for Two Plants
The requirement for multiple plants is due to a natural defense mechanism known as self-incompatibility (SI). Tomatillos possess a genetic system that actively prevents fertilization by their own pollen. This system ensures genetic diversity by forcing the plant to rely on cross-pollination with a genetically distinct partner.
The flowers contain both male (pollen) and female (pistil) reproductive parts, but the self-incompatibility mechanism rejects its own pollen. The plant’s pistil recognizes and inhibits the growth of the pollen tube from its own flower or from a flower on the same plant. Therefore, pollen must come from a separate, unrelated tomatillo plant for the fruit-setting process to successfully begin. Planting two plants propagated from a single cutting will not work, as they are genetically identical.
Optimizing Cross-Pollination
Successful cross-pollination requires the activity of external agents to transfer the necessary pollen. Tomatillo pollen grains are relatively heavy and sticky, meaning they are not effectively carried by wind alone. Instead, the plants rely heavily on insects, primarily bees, to physically move the pollen between flowers on different plants.
To facilitate this transfer, plants should be spaced at least two to three feet apart. This spacing allows for proper air circulation and growth, while keeping them close enough for pollinators to easily travel between them.
If natural pollinator activity is low, you can perform manual cross-pollination. This is done by gently collecting pollen from a flower on one plant using a small brush or cotton swab, and then immediately transferring it to a flower on the second plant. This process must be repeated between the two distinct plants for every flower you wish to set fruit.
Identifying and Resolving Low Fruit Production
Even when two plants are present, gardeners sometimes observe low yields, such as a large number of flowers that drop off without forming fruit.
Nutrient Imbalance
A common cause is an imbalance in soil nutrients, specifically an excess of nitrogen. This encourages the growth of lush leaves at the expense of flower and fruit development. To resolve this, switch to a fertilizer that is lower in nitrogen and higher in phosphorus and potassium.
Environmental Stress
Environmental stress can also stop fruit production, especially when temperatures consistently rise above 85°F or humidity exceeds 90%. High heat can cause flowers to abort or produce non-viable pollen, leading to flower drop. Ensuring a consistent water supply and applying a thick layer of mulch can help mitigate heat stress.
Pollination Failure
If you have two plants but still see only empty husks, the issue may be a lack of effective pollen transfer. This signals a need to increase pollinator access or begin a routine of hand-pollination.