We love discussing how combining different plants in your greenhouse can be a great idea! Companion planting is fantastic, but it's important to do it correctly to get the best results.
Just like some people don't get along, some plants don't either! Fennel and nightshades are like bad neighbors and can harm each other if planted too close.
Why Are Fennel and Nightshades Incompatible?
Imagine doing all the necessary watering and fertilizing, only to have poor germination and stifled plant growth in your greenhouse nursery and vegetable greenhouse. This can be confusing and disheartening!
Nightshades include plants like peppers, tomatoes, eggplants, and potatoes. These plants are popular in many gardens due to their versatility and nutritional value.
When grown alone or with good companion plants, they thrive and produce excellent harvests. However, it's crucial to avoid growing them beside fennel plants.
Nightshade plants have high alkaloid content, which serves several purposes:
- Natural pest repellent: The alkaloids make nightshades less appealing to certain pests, offering some natural protection.
- Flavor profile: These compounds contribute to the distinct flavors of nightshade vegetables.
- Potential health benefits: Some alkaloids have been studied for their potential medicinal properties.
Despite these benefits, the high alkaloid content can be harmful to some plants, with fennel being a prime example. Fennel is not a nightshade but a perennial herb.
The chemical interaction between nightshades and fennel can lead to:
- Reduced seed germination rates
- Stunted growth in both plants
- Decreased fruit production
- Altered flavor profiles in the vegetables
A Two-Way Toxic Relationship
This toxic relationship is a two-way street. Although fennel plants may seem harmless on the surface, their allelopathic compounds have growth-inhibiting effects on some plants.
This herb will make your nightshades struggle to germinate, grow and produce fruit. The fruits produced will be lesser and more minor than the plants could have made if not planted close to fennel.
Nutrient and Soil Requirements
Another reason you should think twice before mixing these greenhouse plants is their nutrient and soil requirements.
- To grow a bountiful tomato, eggplant, and pepper harvest, your soil must be slightly acidic with a pH of 6.0 to 6.8.
On the other hand, excellent fennel production will be from alkaline soil with a pH of 7.0 to 8.0.
- Fennel should get fertilizer with NPK 20-5-5, while nightshades will grow with NPK averages of 5-10-10.
Since the growing requirements differ, you must place them in different beds or the fennel in your herb greenhouse. Improper fertilization can cause stunted growth for both plants.
Spacing and Sunlight Considerations
Proper spacing is the final factor to consider when planting these two crops. Fennels will grow well when grown well in clusters and have lots of sunlight. Nightshades require more space to thrive. If planted close to fennels, they will tower over them, blocking the sunlight and affecting their growth.
Fennel Spacing and Sunlight Needs
- Clustering: Fennels grow well when planted in clusters. This planting method allows them to support each other and creates a more attractive display.
- Spacing within clusters: Plant fennel seeds or seedlings about 4-6 inches apart within each cluster.
- Between clusters: Leave about 12-18 inches between clusters to allow for proper air circulation.
- Sunlight requirements: Fennel thrives in full sun, needing at least 6-8 hours of direct sunlight daily.
- Height: Fennel plants typically grow to a height of 3-5 feet, depending on the variety.
Nightshade Spacing and Sunlight Needs
Unlike fennel, nightshades generally require more individual space to grow properly.
- Tomatoes: 18-24 inches apart
- Peppers: 12-18 inches apart
- Eggplants: 18-24 inches apart
Rows of nightshades should be spaced 2-3 feet apart to allow for easy access and maintenance.
Also, most nightshades also prefer full sun, needing 6-8 hours of direct sunlight daily.
Nightshade heights can vary significantly:
- Determinate tomatoes: 2-3 feet
- Indeterminate tomatoes: Can reach 6-8 feet or more
- Peppers: Generally 1-3 feet
- Eggplants: Usually 2-4 feet
Keep Fennel and Nightshades Separate for Successful Gardening
So, before planting in your greenhouse, remember that not all plants get along. Even though companion planting can be a great idea, it's essential to do it correctly to get the best results.
Fennel and nightshades are like bad neighbors that can harm each other if planted too close.
Due to this toxic relationship, don't be disheartened when your plants don't grow as well as you expected. It's essential to consider the nutrient and soil requirements and proper spacing when planting them.
Ready to get started with your greenhouse garden? Explore our DIY greenhouse kits or explore our growing guides to create the ideal environment for your fennel and nightshades.
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