How to Control Water Weeds How to Control Water Weeds

What You'll Need
Plant Shears
UV filter
Planting baskets

Water gardens can be difficult to maintain. You must control water weeds in order to maintain a healthy ecosystem, and the best way to do this is by preventative measures. However, once you have a weed infestation, the plants must be identified and quickly removed.

Step 1 - Prevention 

There are several things that prevent weeds from taking hold in your garden. Algae, the most common of water weeds, are naturally occurring and nearly impossible to eradicate. If kept in balance, however, you may never see it. Algae blooms occur when there are enough resources in their environment for them to replicate faster than they are dying off. Algae feed off nutrients like nitrogen in the water, and they use sunlight to make their own food.

There are several ways to keep algae in check. A UV filter sterilizes water, quickly killing off algae. Keep in mind that the strength of your UV filter must be proportional to the size of your garden as well as the condition it’s in. 

  • If you live in a warm climate and keep fish, you will need a larger filter.
  • Keep nutrient levels in check to help control algae populations.
  • Keep fish population sizes low and feed them only what they can eat within a half-hour.
  • Keep plant fertilizers at a minimum, and plant shade-producing plants to block sunlight.
  • If these things fail, add beneficial bacteria or barley straw concentrate to your water. You can also use algaecide, though this is not recommended—it can harm fish, plants and other wildlife.

Keeping populations of desired plants under control can keep them from becoming a weed problem elsewhere in your garden. Using planting baskets is especially helpful for this application.

If your garden is large enough to attract water fowl, discouraging them will reduce instances of duckweed and water fern. It is important to be vigilant when fighting these types of weeds. A waterfall or fountain combined with daily inspection and removal will keep weed populations from establishing.

Step 2 - Identification of Weeds 

When combating an established water weed infestation, first identify the plant you are trying to eliminate. If the species of plant replicates by seeding, remove the plant before it goes to seed, or remove all seeds that it has dropped.  

If the plant is asexual and sends out runners to replicate, you must remove all roots. Water lilies are one type of plant that sends out runners and produces seeds, so both must be removed. Some plants can also be cut back to keep them from spreading. 

Step 3 - Weed Removal 

For best results, do most weeding by hand. This way, you won’t disturb any other plants. Use a rake to skim the surface of the water. Herbicides are not recommended as they can damage wildlife and other plants.

  • Blanket weed, a type of algae, can be skimmed from the top of the water. 
  • Submerged weeds can be removed by raking or cutting. 
  • Free-floating plants like duckweed and water fern can be removed by rake or net.

Emergent weeds, such as yellow flag iris or reeds, must be removed by the roots. If you want to keep a population, but it is getting out of control, lift the plant, divide it and replant. Cutting, especially in late summer, can also limit re-growth.

For floating leaved plants, like water lilies, all parts of the root and any seeds must be removed. If this a desired plant that has spread, it can be cut back for short-term removal. 

Step 4 - Clean-up

Make sure you remove all debris. This will prevent rot and keep water clear.

Be careful when disposing of water weeds as many species are invasive. Compost, burn or burry them to prevent spread into natural habitats. 

Following these simple steps to maintain a healthy, weed free environment will make your water garden a success.

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