Exotic Pest Plants

Seasonal Gardening Tips

Plant beets now for fall harvest. They will have a deeper red color than beets planted for spring harvest and tend to have higher sugar levels too. Fall vegetables can be planted now for a fall harvest of broccoli, Brussels sprouts, cabbage, chard, and lettuce.

Trim grapevines to allow more sun to reach the fruit and sweeten the grapes if they are being heavily shaded by foliage. Feed fuchsias, begonias, summer annuals, and container plants to keep them green and blooming right up until frost. Divide Oriental poppies and bearded iris now. Add some bone meal in the bottom of the hole when you replant them.

Exotic Pest Plants

For many decades, the nursery trade has been introducing plants gathered from around the world into our gardens. Any plant that is not native to an area is called an “exotic.” Most exotics are great additions to our gardens and often tolerate garden conditions better than native shrubs. However, when an exotic plant becomes a weed, reproducing on its own in the wild, it is considered a pest plant. Examples include:

• Pampas grass, introduced from South America, now grows wild along coastal areas of California.
• Scotch broom, which thrives in disturbed soil such as along roadsides, is also a significant problem in this county.

These plants become problematic because their success in non-native areas crowds out native plants critical for the survival of native birds and other wildlife. Many pest plants are weeds even in their native environments. For instance:

• Yellow star thistle, introduced from Russia in the 19th century via alfalfa hay, now covers countless acres of California’s hillsides, giving them a bluish cast.

Some pest plants were intentionally sold by nurseries for ornamental purposes but later became invasive. An exotic plant’s ability to reproduce depends on optimal conditions, so a particular pest plant may only be problematic in certain regions. Many invasive plants are especially troublesome in wet areas or around ponds, such as:

• Cattails and umbrella plant, which spread by both roots and seeds.
• Yellow water iris, which has aggressive roots that can quickly fill a small pond.

Managing Invasive Plants

If you have invasive plants on your property, try suffocating small seedlings and annual plants using double layers of thick UV-stabilized plastic sheeting (clear or black). Secure the plastic with stakes or weights, ensuring it extends at least five feet past the edge of the infestation on all sides. Leave the plastic in place for at least two years. Note that this method will kill everything beneath the plastic, including non-invasive plants. After removing the plastic, sow a cover crop like annual rye to prevent new invasions.

Mowing or cutting plants down to the ground is also effective but requires commitment. You will need to mow the area three or four times a year for up to five years to exhaust the root system and kill the plants.

Herbicides are another option but must be used with caution. Be mindful when selecting plants for wild areas of your property to avoid contributing to the problem.