Invasive Garden Plants

Most gardeners are aware of the problems that weeds can cause in the garden, but there are some plants that we can buy that can cause just as much of a problem. We can easily purchase these "thug" plants that, once established in our planting schemes can run amok! The following will take a look at those plants that can be described as invasive and what we can do about them.

What are Invasive Garden Plants?

Invasive plants are those that can quickly get out of hand in the garden, even though they are not regarded as weeds and are commonly sold in garden centres. The following is a list of plants that can be labelled "invasive":

• Leyland Cypress (x Cupressocyparis leylandii)
• Poplars (Populus sps.)

• Russian vine (Fallopia baldschuanica)

• Sasa palmata
• Phalaris arundinacea
• Phragmites australis
• Weeping sedge (Carex pendula)

• Japanese anemone (Anemone x hybrida cultivars)
• Houttuynia cordata ‘Chameleon'
• Yellow loosestrife (Lysimachia punctata)
• Golden rod (Solidago canadensis)

• Mind-your-own-business (Soleirolia soleirolii)

• Blackberries
• Raspberries
• Horseradish
• Mint

• Leptinella squalida
• Pratia pedunculata
• Snowberry (Symphoricarpos albus)
• Periwinkle (Vinca major and V. minor)
• Gaultheria shallon
• Hypericum calycinum

• Lesser celandine (Ranunculus ficaria) cultivars
• Oxalis culitvars
• Allium paradoxum and A. triquetrum

• Crassula helmsii (New Zealand pygmy weed)
• Myriophyllum aquaticum (parrot's feather)
• Azolla filiculoides (fairy fern)
• Hydrocotyle ranunculoides (floating pennywort)

This is not to say that you should never choose these plants for your garden! Manyof the plants listed above are beautiful and will add interest to your planting scheme. Simply consider carefully the plant you are choosing to ensure your garden can cope with its demands and also be prepared to carry out heavy pruning, digging or thinning to control the plant

The Problems

So why are some plants so problematic? A lot of the problem is simply due to the way the plant grows. Trees like the Leyland cypress and climbers such as Russian vine can grow so quickly that they are soon much too big for the garden. Trees such as poplar have a tendency to sucker, sending up shoots all over the garden and even in neighbours' properties.

Many ground cover shrubs like the snowberry or Hypericum calycinum spread via underground stems (rhizomes), sending up new plants and gradually taking over the border. Some bamboos also behave in this way.

Potentially invasive herbaceous plants and grasses, such as Japanese anemones and Phalaris arundinacea, form ever-enlarging clumps that require frequent division. Others, such as golden rod or weeping sedge also spread by seed, with seedlings popping-up in unexpected places where they are not wanted.

Bulbous plants such as Oxalis can produce tiny new bulbs, or offsets, which are scattered every time a clump is dug up, spreading the problem rather than controlling it.

Control

So what can you do? Primarily, avoid choosing plants that you believe will cause you problems! Pay careful attention to the growth habits of any plant you are tempted to buy and consider how it would fit in your garden - if you have a small garden then a fast growing plant is not the thing to select!

Digging out unwanted plants may work for a while, but is only likely to be a temporary solution. Judicious use of weedkillers may be necessary. For herbaceous weeds, try a programme of spraying using a systemic herbicide containing glyphosate. For woodier plants, choose a stump or brushwood killer.

If you really have fallen in love with what can be considered an invasive plant then ensure you monitor its growth and spread and be prepared to work hard to keep it under control.