Mastering Your Greenhouse: What Not to Grow for Optimal Success
Greenhouses are fantastic tools for extending your growing season, protecting delicate plants from harsh weather, and even growing things that might not thrive outdoors in your region. However, not every vegetable is a good candidate for greenhouse cultivation. In fact, attempting to grow certain vegetables in a greenhouse can lead to disappointment, wasted resources, and even unhealthy plants. Understanding which vegetables are best left to the great outdoors is crucial for maximizing your greenhouse's potential and ensuring a bountiful harvest.
Why Some Vegetables Don't Belong in a Greenhouse
The primary reasons certain vegetables fare poorly in a greenhouse environment boil down to a few key factors:
- Space Requirements: Many vegetables, especially those that sprawl or grow very large, simply need more room than a typical greenhouse can comfortably provide.
- Pollination Needs: Some plants require specific conditions or pollinators (like bees) that are absent or less effective in a sealed greenhouse environment.
- Environmental Preferences: Certain vegetables thrive on the fluctuations of outdoor weather, including wind, rain, and natural temperature swings. A static greenhouse environment can hinder their development.
- Disease and Pest Susceptibility: While greenhouses can protect from some pests, they can also create ideal breeding grounds for others if not managed meticulously. Some plants are also more prone to specific diseases in enclosed, humid conditions.
- Economic Viability: For many gardeners, the cost of heating, cooling, and maintaining a greenhouse for crops that grow perfectly well outdoors just isn't a wise investment.
Specific Vegetables to Avoid in Your Greenhouse
Let's dive into some common vegetables that are generally not recommended for greenhouse growing, along with the reasons why:
Root Vegetables That Need Room to Spread
While some smaller root vegetables like radishes can be grown in containers within a greenhouse, larger or more extensive root crops are usually a poor choice.
- Potatoes: Potatoes require significant space for their tubers to develop underground. A greenhouse typically doesn't offer enough depth or width for optimal potato production. Furthermore, they benefit from the natural aeration and drainage of open soil.
- Carrots: While you can grow shorter varieties of carrots, long, slender carrots need deep, loose soil and ample space to form properly. Trying to cultivate them in limited greenhouse space can result in stunted or deformed roots.
- Beets: Similar to carrots, beets need room to develop their taproots. Overcrowding in a greenhouse can lead to smaller, less flavorful beets.
- Sweet Potatoes: These are sprawling vines that require extensive space to grow both above and below ground. A greenhouse is simply too confining for their vigorous growth habit.
Vining and Bushy Plants Requiring Abundant Space
Many of our favorite summer staples are vining or bushy plants that can quickly outgrow the confines of a greenhouse.
- Corn: Corn plants are tall and need ample spacing for proper pollination. They also require a significant amount of light, which can be difficult to consistently provide for a large number of corn stalks within a greenhouse.
- Melons (Watermelon, Cantaloupe, Honeydew): These are sprawling vines that produce heavy fruits. They need a lot of horizontal space to spread out and often benefit from natural pollination by bees. While some smaller varieties can be trellised, they still demand a lot of room.
- Squash (Winter and Summer varieties): Most squash varieties, especially winter squash, are heavy, vining plants that take up considerable space. Even summer squash plants can become quite large and bushy.
- Pumpkins: Similar to melons and winter squash, pumpkins are massive vining plants that require extensive room to grow and spread.
- Peas (Bush varieties can be okay, but pole beans are often better outdoors): While some compact bush pea varieties might manage in a greenhouse, pole beans, which are prolific climbers, can become unwieldy and require a lot of vertical and horizontal space.
Crops That Need Outdoor Conditions for Optimal Growth
Some vegetables have specific environmental needs that are best met by the natural outdoor world.
- Broccoli, Cauliflower, Cabbage, and other Brassicas: These cool-season crops often prefer the natural temperature fluctuations and breezes of the outdoors. In a consistently warm greenhouse, they can become leggy, prone to bolting (going to seed prematurely), and susceptible to specific pests like cabbage worms and aphids that can thrive in the controlled environment.
- Asparagus: Asparagus is a perennial crop that requires years to establish and needs ample ground space. It also benefits from a period of dormancy that is naturally provided by outdoor winter conditions.
- Rhubarb: Another perennial that requires significant space and benefits from outdoor winter chilling for optimal growth and flavor.
- Onions and Garlic (for bulb formation): While you can grow green onions or scallions in a greenhouse, forming large bulbs of onions and garlic requires specific soil conditions and a longer growing season that is often more efficiently achieved outdoors. They also need good air circulation to prevent rot.
When in Doubt, Consider Your Space and Goals
Before planting anything in your greenhouse, ask yourself:
- Does this plant need a lot of horizontal or vertical space?
- Does this plant rely heavily on outdoor pollinators?
- Are the environmental conditions in my greenhouse ideal for this specific plant, or would it thrive better with natural weather fluctuations?
- Is the potential yield worth the space and resources I'd be dedicating in my greenhouse?
By understanding which vegetables are not suited for greenhouse cultivation, you can focus your efforts on crops that will truly benefit from this protected environment, leading to healthier plants and a more satisfying harvest. Leave the space-hogs and outdoor enthusiasts to the garden beds, and let your greenhouse become a haven for heat-lovers and season-extenders!
Frequently Asked Questions (FAQ)
Can I grow any root vegetables in a greenhouse?
Yes, you can grow smaller root vegetables like radishes and short varieties of carrots in containers within a greenhouse. However, larger root crops like long carrots, potatoes, and beets are generally not recommended due to their space requirements for proper root development.
Why are melons and squash not good for greenhouses?
Melons and squash are often sprawling, vining plants that require a significant amount of horizontal space to grow and produce fruit. They also benefit from open-air pollination by bees, which may be less prevalent or effective in a closed greenhouse environment. Their sheer size can quickly overwhelm the limited space of most greenhouses.
How does a greenhouse affect cool-season crops like broccoli?
Greenhouses tend to create consistently warmer temperatures, which can cause cool-season crops like broccoli, cauliflower, and cabbage to bolt (go to seed prematurely), become leggy, or be more susceptible to certain pests like aphids and cabbage worms that thrive in enclosed, humid conditions. They often prefer the natural temperature fluctuations of the outdoors.
Are there any exceptions to these rules?
Yes, there can be exceptions. For example, with extensive trellising systems and careful management, some gardeners may successfully grow smaller varieties of vining plants in larger greenhouse spaces. However, for the average home gardener, it's generally more efficient and productive to reserve greenhouse space for crops that truly benefit from protection and accelerated growth, rather than struggling with plants that have extensive space or specific outdoor environmental needs.
