Incompatible garden plants are those that should not be grown together because they may interfere with each other's growth or cause harm. 

Incompatible Garden Plants

Some plants dislike each other and can be harmful in several ways, including:

1. Competing for resources: Plants with a similar root system, such as trees and shrubs, may compete for water and nutrients in the soil. This can cause one plant to grow poorly and become more susceptible to diseases.

2. Releasing allelopathic chemicals: Some plants release chemicals into the soil that can be toxic to other plants. This is known as allelopathy, and it can occur with many types of plants, including trees, shrubs, and flowers. As an example 

   1. Black walnut (Juglans nigra) - the roots, leaves, and nuts of black walnut trees release a chemical called juglone that can inhibit the growth of many other plants, including tomatoes, potatoes, and peppers.

   2. Sunflowers (Helianthus annuus) - sunflowers release a chemical called allelopathin that can inhibit the growth of other plants, particularly those in the nightshade family.

3. Spreading diseases: Plants can spread diseases to other plants through contact, soil, or airborne spores.

4. Attracting pests: Certain plants can attract pests like insects and rodents that can damage nearby plants.

It's important to consider the interactions between plants when designing a garden or landscape to avoid these negative effects. Companion planting is one way to help mitigate the impact of harmful interactions and promote healthier plant growth.

What Plants Should Not Be Grown Together?

There are some plants that should not be grown together due to their incompatible growing conditions or allelopathic effects. Here are classic examples:

1. Asparagus and onions: Onions can inhibit the growth of asparagus.

2. Beans and onions: Onions can inhibit the growth of beans.

3. Brassicas and nightshades: Brassicas, such as broccoli and cabbage, can stunt the growth of nightshades, such as tomatoes and peppers.

4. Fennel and most other plants: Fennel can produce allelopathic chemicals that can inhibit the growth of most other plants.

5. Potatoes and tomatoes: Both plants are susceptible to the same diseases, such as blight, so planting them together can increase the risk of infection.

6. Corn and tomatoes: Both plants are heavy feeders and can deplete the soil of nutrients.

7. Walnuts and most other plants: Walnuts can release allelopathic chemicals that can harm most other plants.

Examples of Plants That Should Not Be Grown Together

Tips for successful Companion Planting

Here are some tips for successful companion planting:

1. Know your plants: Different plants have different needs and grow best in different environments. Make sure to choose plants that are well-suited to your growing conditions.

2. Plan ahead: Before you start planting, make a plan of where each plant will go. Consider factors such as spacing, sunlight, and water requirements.

3. Plant in groups: Planting in groups can help to create a microclimate that is beneficial to all the plants in the group.

4. Use crop rotation: Crop rotation can help to reduce the risk of disease and pests in your garden.

5. Mix it up: Don't be afraid to mix different types of plants together. This can help to create a more diverse and interesting garden.

6. Be patient: Companion planting takes time to work, so don't be discouraged if you don't see results right away.

7. Experiment: Try different combinations of plants to see what works best in your garden. Keep track of what works and what doesn't so you can make adjustments in the future.