The allure of a greenhouse is undeniable. A controlled environment, extending the growing season, and nurturing delicate plants – it sounds like a gardener’s paradise. However, the reality is that not every plant thrives, or is even suitable, for greenhouse cultivation. Understanding what not to grow in a greenhouse is just as important as knowing what to plant. Making informed decisions can save you time, money, and heartbreak.
Considering the Greenhouse Environment
Before diving into specific plants, it’s crucial to understand the unique environment within a greenhouse. Greenhouses trap heat and sunlight, creating higher temperatures and humidity levels than outdoors. Ventilation is key, but even with good airflow, certain plants are simply not adapted to these conditions. Space limitations are also a significant factor. Towering trees and sprawling vines might seem appealing, but they quickly outgrow the confines of even the largest greenhouses. Let’s consider some of these key limitations.
Temperature and Humidity Issues
High temperatures can be a major limiting factor. Some plants, particularly those from cooler climates, struggle to survive in the consistently warm conditions of a greenhouse. Similarly, elevated humidity levels can encourage fungal diseases and pest infestations that can devastate entire crops. Understanding the temperature and humidity requirements of your plants is crucial before introducing them to a greenhouse.
Space Constraints and Long-Term Viability
The limited space inside a greenhouse is a constraint that often goes overlooked. Plants that grow large quickly can soon take over, shading out other crops and requiring constant pruning. Furthermore, some plants simply aren’t suited for long-term cultivation in a confined space. They may require specific soil conditions, root space, or environmental triggers that are difficult to replicate within the greenhouse environment.
Plants Unsuitable for Greenhouse Cultivation
Now, let’s delve into specific plant categories and examples of plants that are generally unsuitable for greenhouse cultivation. This is not an exhaustive list, but it covers some of the most common mistakes that gardeners make.
Large Trees and Shrubs
This might seem obvious, but it’s a mistake that’s often made in the initial enthusiasm of setting up a greenhouse. Fruit trees like apples, pears, and cherries, as well as large shrubs like lilacs and hydrangeas, are simply too large for most greenhouses. Even dwarf varieties eventually outgrow their space. Furthermore, these plants typically require a period of dormancy induced by cold temperatures, which is difficult to replicate consistently in a greenhouse.
Plants Requiring Cold Stratification
Many plants, particularly perennials and some annuals, require a period of cold stratification for their seeds to germinate properly. This means that the seeds need to be exposed to cold temperatures for a certain period of time before they will sprout. This process is difficult to replicate in a greenhouse, where temperatures are generally warm. Examples include many wildflowers, some types of berries, and certain tree species. Attempting to grow these plants in a greenhouse without proper cold stratification will often result in poor germination rates or complete failure.
Plants Susceptible to Common Greenhouse Pests and Diseases
Greenhouses, while offering a controlled environment, can also become breeding grounds for pests and diseases. The warm, humid conditions are ideal for many common greenhouse pests, such as aphids, spider mites, and whiteflies. Certain plants are particularly susceptible to these pests, making them a poor choice for greenhouse cultivation. Similarly, some plants are prone to fungal diseases like powdery mildew and botrytis, which thrive in humid conditions. Roses, for example, are notoriously susceptible to black spot and powdery mildew in humid environments, making them a high-maintenance choice for greenhouse cultivation.
Plants Needing Open Pollination
Some plants rely on wind or insects for pollination. In a closed greenhouse environment, these plants may struggle to produce fruit or seeds. While hand-pollination is an option, it can be time-consuming and may not be as effective as natural pollination. Plants like corn, which rely on wind pollination, are particularly difficult to grow successfully in a greenhouse. Similarly, plants that require specific pollinators, such as certain types of squash, may not thrive unless you introduce the necessary insects into the greenhouse.
Wild Plants and Plants from Specific Habitats
Attempting to transplant wild plants or plants adapted to very specific habitats into a greenhouse environment is often a recipe for disaster. These plants may have highly specialized soil requirements, light preferences, or temperature needs that are difficult to replicate in a controlled environment. For example, trying to grow desert cacti in a humid greenhouse will likely lead to root rot and death. Similarly, plants that are adapted to high-altitude environments may struggle to survive in the warmer, lower-altitude conditions of a greenhouse. Respecting the natural habitat of plants is crucial for their survival.
Specific Plant Examples to Avoid
Let’s look at some specific plants that are often attempted in greenhouses but generally prove to be problematic.
- Corn: As mentioned earlier, corn requires wind pollination and a significant amount of space, making it unsuitable for greenhouse cultivation.
- Sunflowers: These towering plants quickly outgrow most greenhouses and require a lot of sunlight, which can be difficult to provide consistently.
- Large Fruit Trees (Apples, Pears, Cherries): Their size and dormancy requirements make them impractical for greenhouse growing.
- Rhododendrons and Azaleas: These acid-loving plants often struggle in the alkaline environment of greenhouse soil.
- Most Wildflowers: Their specific habitat and pollination needs make them difficult to cultivate successfully in a greenhouse.
- Open-Field Vegetables (Potatoes, Sweet Potatoes): These vegetables need a large area of soil for proper root development.
- Asparagus: This perennial vegetable needs several years to mature before it is ready for harvesting and takes up significant space.
- Certain Herbs (Lavender, Rosemary): Although seemingly simple, lavender and rosemary need extremely well-draining soil and dry conditions, which are hard to provide in a greenhouse.
Strategies for Successful Greenhouse Growing
While certain plants are best avoided, many others thrive in a greenhouse environment. The key is to choose plants that are well-suited to the conditions and to implement proper greenhouse management practices.
Selecting Appropriate Plants
Focus on plants that benefit from the controlled environment of a greenhouse, such as tomatoes, peppers, cucumbers, and herbs that enjoy warmth and humidity. Start with seedlings that are already established, and choose varieties that are known to perform well in greenhouse settings. Consider vertical gardening techniques to maximize space utilization.
Managing Temperature and Humidity
Invest in proper ventilation systems, such as exhaust fans and vents, to regulate temperature and humidity levels. Use shade cloth to reduce sunlight intensity during the hottest months. Consider using a humidifier or dehumidifier to maintain optimal humidity levels. Monitor temperature and humidity levels regularly using a thermometer and hygrometer.
Pest and Disease Control
Implement preventative measures to minimize the risk of pest and disease outbreaks. Use sterile potting mix, regularly inspect plants for signs of pests or diseases, and remove any infected plants immediately. Introduce beneficial insects, such as ladybugs and lacewings, to control pest populations. Use organic pesticides and fungicides as needed, following label instructions carefully.
Proper Watering and Fertilization
Water plants deeply but infrequently, allowing the soil to dry out slightly between waterings. Avoid overwatering, which can lead to root rot. Use a balanced fertilizer to provide plants with the nutrients they need. Monitor plant growth and adjust fertilizer applications as needed.
Conclusion
A greenhouse can be a valuable asset for gardeners, but it’s important to be aware of its limitations. Choosing the right plants and implementing proper management practices are essential for success. By avoiding the plants listed above and focusing on those that thrive in a greenhouse environment, you can create a productive and enjoyable growing space. Remember, careful planning and informed decision-making are the keys to a successful greenhouse gardening experience.
What types of plants are generally unsuitable for greenhouse cultivation due to their large size or growth habits?
Extremely large trees and shrubs are generally unsuitable for greenhouse cultivation. Their massive root systems can quickly outgrow even the largest containers, and their mature size often exceeds the available headroom, requiring constant pruning that compromises their natural form and fruit production. Additionally, attempting to grow these plants in a controlled environment can be economically inefficient, as the energy required to maintain optimal conditions for such a large volume of plant material becomes prohibitively expensive.
Vigorous vining plants that aggressively spread can also pose challenges in a greenhouse. While some vining plants are suitable, varieties with unrestrained growth, such as certain types of ivy or wisteria, can quickly overwhelm other plants, block sunlight, and create a maintenance nightmare. Their rapid growth requires constant monitoring and pruning, consuming valuable time and resources that could be better allocated to more manageable and productive greenhouse crops.
Why might growing specific field crops, like corn or wheat, in a greenhouse be a costly mistake?
Field crops like corn and wheat are adapted to large-scale cultivation in open fields, utilizing natural rainfall and sunlight. Replicating these conditions within a greenhouse environment is incredibly inefficient. The artificial lighting, irrigation, and ventilation required to support these crops on a smaller scale incur significant expenses that often outweigh any potential yield benefits. The very nature of these crops makes them unsuitable for enclosed spaces.
Furthermore, the pollination mechanisms of many field crops are wind-driven, which is difficult to simulate effectively inside a greenhouse. Without proper pollination, these crops will not produce the desired grain or fruit, rendering the entire endeavor futile. The space utilization efficiency is also significantly lower compared to higher-value crops better suited for greenhouse environments, exacerbating the financial losses.
What are the risks associated with growing plants that are highly susceptible to specific greenhouse pests or diseases?
Introducing plants that are known to be magnets for common greenhouse pests, like spider mites, aphids, or whiteflies, can quickly lead to widespread infestations. These pests can rapidly multiply in the controlled environment, spreading to other susceptible plants and causing significant damage. The cost of controlling these infestations, including pesticides and labor, can quickly escalate and significantly reduce profitability.
Similarly, plants that are prone to greenhouse diseases, such as powdery mildew, botrytis, or root rot, pose a major threat to the entire greenhouse ecosystem. The humid and enclosed environment can create ideal conditions for these diseases to thrive, leading to rapid spread and potentially devastating losses. Preventive measures and aggressive treatment are costly and time-consuming, making it often more economical to avoid growing these plants altogether.
Why is it important to consider the pollination requirements of a plant before growing it in a greenhouse?
Many fruiting and flowering plants rely on insects, wind, or other external agents for pollination. A greenhouse, by its enclosed nature, can limit or eliminate these natural pollination mechanisms. Without proper pollination, these plants will fail to produce fruit or seeds, rendering them unproductive and a waste of valuable greenhouse space. It’s crucial to assess a plant’s pollination needs before committing to its cultivation in a controlled environment.
While manual pollination or the introduction of pollinators like bees or bumblebees are possible solutions, these options require additional effort, resources, and careful management. Manual pollination is labor-intensive, and introducing pollinators can pose challenges related to their health, containment, and potential impact on other greenhouse inhabitants. Selecting self-pollinating varieties or those that readily hybridize indoors can be a more practical and cost-effective approach.
How can climate preferences make certain plants unsuitable for greenhouse growing alongside other crops?
Greenhouses are typically designed to maintain a relatively uniform climate suitable for a range of plants. However, if you introduce plants with drastically different climate requirements, such as those needing extreme humidity or temperature variations, it can create significant challenges. Attempting to cater to these specific needs may compromise the optimal growing conditions for other plants in the greenhouse.
For example, trying to grow tropical plants requiring consistently high humidity alongside plants that prefer dry conditions can lead to disease outbreaks in the humid-loving species or stunted growth in the drought-tolerant ones. Maintaining separate zones within a greenhouse to accommodate different climate preferences can be costly due to the need for additional heating, cooling, and humidity control equipment, making it more practical to select plants with compatible needs.
What role does the economic viability of a plant play in determining its suitability for greenhouse cultivation?
While some plants may technically be able to grow in a greenhouse, their economic viability should be carefully considered. High-value crops that command premium prices, like specialty herbs, rare vegetables, or out-of-season fruits, are generally better suited for greenhouse cultivation than low-value crops that can be easily and cheaply grown outdoors. The costs associated with operating a greenhouse, including energy, labor, and maintenance, need to be justified by the potential revenue generated.
Before deciding to grow a particular plant, conduct a thorough market analysis to determine the potential demand and selling price. Compare the anticipated revenue with the estimated costs of greenhouse cultivation, including the specific inputs required for that plant, such as specialized fertilizers or pest control measures. If the profit margin is too small or nonexistent, it may be more economically sound to focus on alternative crops that offer a better return on investment.
Why should the invasive potential of a plant be considered before growing it in a greenhouse environment?
Even within the controlled environment of a greenhouse, the invasive potential of certain plants can pose significant problems. While physical barriers may prevent escape into the wider ecosystem, an aggressively invasive plant can quickly dominate the greenhouse, outcompeting other crops for resources like light, water, and nutrients. This can lead to reduced yields and overall diminished productivity.
Furthermore, removing invasive plants from a greenhouse can be extremely difficult and time-consuming. Their tenacious growth habits and ability to reproduce rapidly often necessitate the use of herbicides or other control methods that may be harmful to other plants or the environment within the greenhouse. Choosing non-invasive varieties or implementing strict containment measures are crucial to prevent these issues and maintain a healthy and productive greenhouse environment.