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A close-up capture of small garden waterfall with pond with aquatic plants and flowing water surrounded by slabs of sandstone rock and patches of fern and weeping maple tree in autumn season colors.

Pond Plants & Water Feature Maintenance

Bring your garden’s water features to life with the beauty and balance of aquatic and marginal plants.

Water Feature Maintenance

There are three main categories of pond plants—hardy, semi-tropical, and tropical—and you can learn all about them below!

Spring Pond Care

Pond plants are the primary ingredient in any recipe for a healthy pond. They help create healthy healthy water by adding shade, removing excess nutrients and toxins, and adding oxygen to refresh the water.

Every spring, it’s important to cut back any dead foliage remaining on your pond plants from the previous season. This allows room for new growth and prevents the accumulation of additional organic material in the pond. Be sure to cut back only those plants which put out leaves and flowers on new (rather than old) growth. If the plants are hollow-stemmed, cut stems above the water line so the rootstock will not fill with water and rot.

It is also important to remove decaying leaves and other organic material that have settled to the bottom of the pond during fall and winter. The easiest method is to use a skim net to remove the larger debris. Fine sediment will usually pass through the skim net and remain on the pond bottom. If there is an excessive amount of debris in the pond, the best option may be to drain and clean it. This can be accomplished using a submersible pump placed in the deepest section to first drain the pond.

You can then take a garden hose and continually flush water towards the pump until the pond bottom is clean, or use a Shop Vac to remove the last inch or two of water and sediment. Draining the pond is usually a last resort because you must find a suitable place to house your fish while you clean the pond, and then rebalance the water once the pond is refilled.

Spring is also primetime for fertilizing your pond plants. A good rule of thumb is to wait until the plants begin to show signs of growth. We are located in USDA Zone 8, and typically begin fertilizing marginal plants in March and waterlilies in April. Be sure to use a time release fertilizer specifically designed for aquatic plants.

In preparation for the upcoming season, check your plants to see if any of them need to be divided or transplanted. The best time to divide or transplant aquatic plants is when they begin active growth. This gives plants the opportunity to rapidly develop new roots and thrive.

Some people choose to plant directly in the bottom of the pond while others prefer planting in containers. Planting in mesh baskets works extremely well. Pea gravel works well as a planting media for most marginal plants, and helps to keep the water from becoming cloudy from soil escaping the pot. For waterlilies, we recommend a heavy clay soil or sandy loam, which will bind more nutrients for these heavy feeders. If desired, the soil can be topped with pea gravel or small river rock to prevent koi from uprooting the plants. Many pond-keepers also choose to add floating plants, such as Water Hyacinth. Be sure to wait until after the average last frost for your area before adding these semitropicals. For Portland the average last frost is April 15.

With the warmer temperatures of spring, fish typically become more active as they awaken from winter dormancy. Their metabolism takes time to recover after dormancy, so begin to feed fish only when the average pond temperature rises above 50°. Remember not to overfeed. As the fish become more active, it is also important to ensure that pumps and filters are running properly. This includes checking for any damage caused by winter weather. If you have not cleaned your filters during the winter, it is best to thoroughly clean the filter material before restarting in spring. Add beneficial bacteria to biological filters in the spring. The beneficial bacteria help with water clarity and water quality along with preventing the buildup of ammonia and nitrites in the pond.

Fall Cleaning

Fall is an excellent time to catch up on maintenance left over from summer. Any debris or decomposing plant material that accumulates in the pond can not only be harmful to the health of your fish, it can also feed algae when spring arrives. A simple skim net will allow you to remove any surface debris and material that has collected on the bottom. Preventing further debris from falling into the pond is another area not to be overlooked. This can be accomplished by utilizing netting to cover the surface of the pond. While not visually appealing, the netting only needs to remain over the pond for a few weeks to catch most of the leaves.

Pumps

You may choose to remove your pump prior to cold weather, but in our mild climate, you can enjoy water features year around. During short freezes, a running waterfall can successfully keep an open hole in any ice that forms on the pond surface. However, during a prolonged freeze, pumps should be turned off. If your pond completely freezes over, water from the waterfall can spill across the pond surface and out into the surrounding garden. In the case of a stream, the water can freeze in the streambed before it can return to the pond. In either case, the result is an empty pond and possible damage to an overheated pump. Pumps plumbed with flexible PVC hose can be turned off anytime without worry; however, hard PVC pipe can freeze and crack without water circulation. If you have used hard PVC, we recommend that you turn off the pump anyway. It is much cheaper to replace cracked pipe than a burned out pump. Remember, never let the pump freeze!

Feeding Fish

As cold weather approaches, fish metabolism will slow down. For this reason, it is important to have a thermometer to monitor the water temperature and feed fish accordingly. As the water cools, gradually cut back on how often you feed. When temps are below 50°F, stop feeding altogether. It is also a good idea to switch to a wheat germ based food that is easier to digest, yet still allows the fish to continue to bulk up before entering dormancy.

Water Temperature Range Feeding Frequency

  • 50°F and under: No food at all
  • 51° to 60°F: Once per week
  • 60° to 65°F: Every 3-4 days
  • 65° to 75°F: Once per day
  • 75° to 80°F: 2-3 times per day
  • 80° to 85°F: 2-3 times per day, but increase amount to no more than can be consumed in 5 minutes
  • 85°F and higher: Decrease amount due to possible oxygen

Fish & Water Circulation

Waterfalls or fountains add cold air into the pond water. As a result, many people with koi choose to disconnect those features and just circulate water below the surface. Koi owners will also lift the pump off the bottom of the pond, leaving a layer of undisturbed water for the dormant fish. Depending on the stocking level of fish, it should not cause problems if the surface of the pond freezes over for a short period of time; however, many people use a floating pond de-icer to keep a section of the surface open, allowing for gas exchange.

Filters

Most filters are removed from the pond, cleaned, and then stored until the arrival of spring. In the case of a biological filter, the beneficial bacteria are inactive when water temps are below 50-60° F. As a result, it is not necessary to operate the filter throughout the winter. Ultra-violet lights are another component that it is best to remove for the winter. If you choose to leave any filter outside through the winter, it is important to either dry it completely or continuously circulate water through it to prevent freezing and cracking.

 

Algae: The Green Menace

Algae—a growth spurred by excessive organic materials, warm stagnant water, and sunlight—is probably the most vexing problem encountered by pond owners. While it can be an ongoing concern, there are steps you can take to either prevent or limit its presence in the garden.

dsIt’s important to keep the pond free of unwanted organic material like leaves and other debris–including dead foliage from your pond plants. Do not overfeed fish. Undigested fish food is the primary pollutant in many ponds–as is digested fish food. Most fish ponds, koi ponds in particular, require a bio-filter unit to deal with the fish waste. Bio-filters are great for any pond because they enhance the natural biological activity. When paired with an ultraviolet light, which kills all free-floating algae, you are well on your way to having crystal clear water.

Keep your pond water pH close to neutral. High pH is hard on fish and plants, but it also encourages algae blooms. To avoid stagnant water, add supplemental oxygen. This can be done with the addition of a waterfall, stream, or fountain. High levels of oxygen promote natural biological activity. Shady ponds can be an exception: they are more likely to reach a natural balance without added water movement. Stagnant water is also an invitation to mosquitoes. Small fish & tadpoles can be added to eat mosquito larvae or you can use Mosquito Dunks—a safe, effective, and natural biological form of control.

Don’t change your water unnecessarily. Each time new water is added to a pond, whether it comes from a well or a city water supply, it brings along high levels of free floating nutrients such as phosphate, which can quickly cause an algae bloom. Dechlorinate new water you add. Besides burning the gills of your fish, chlorinated city water can quickly wipe out your colony of natural beneficial bacteria. Bacterial organisms are a necessary component of healthy ponds. They consume excess organic material and toxins in the water, processing them into basic nutrients in a form that plants can use. In a new pond or in one that is out of balance, we always suggest that you add beneficial bacteria to boost normally developing colonies.

Never scrub your pond “clean”. The natural green velvet coating that develops on the sides and bottom of the pond is home to your beneficial organisms. Small fish will eat some algae, but don’t count on them to keep your pond algae-free (they usually add more waste than they consume). Snails are great scavengers and will happily eat filamentous algae. Tadpoles are also algae consumers.

Please do not add Bullfrog tadpoles to your pond. They are non-native predators of our native Tree Frog. Due to the Bullfrog’s voracious appetite, it is feared that native Tree Frogs may completely disappear from the Pacific Northwest. Bullfrogs will also eat your small fish.

And finally, remember: bare expanses of open water are much more difficult to maintain than ponds filled with robust and beautiful water plants.

EXPLORE MORE POND PLANTS

Hardy water plants will over-winter in your pond without requiring any special care and then regrow in spring. The majority of plants we sell fall into this category, including hardy waterlilies. Hardy waterlilies will over-winter as long as their crowns do not freeze. In the Willamette Valley, a depth of 18-24” is usually sufficient. There are a few hardy plants, such as Saururus cernuus (aka lizard’s tail), that require some protection. Plants like this should be dropped deeper so that the top of the pot is at least six inches under the water to protect the plant from freezing.

These will over-winter with some protection. Although many pond owners simply drop them to the deepest section of the pond (at least 18” deep), it is safer to bring the plant into an unheated garage or cold frame. It is important not to let the plant completely dry out. These are just a few semi-tropical pond plant options:

  • Canna species
  • Cyperus alternifolius (umbrella palm)
  • Hedychium coronarium (butterfly ginger)

These don’t go dormant in the winter and will require a protected environment, such as a heated greenhouse, where they can receive necessary warmth and light to continue growing. Given proper growing conditions, including water and light, many tropical plants can also make good houseplants throughout the winter. Tropical pond plant options include:

  • Alternanthera rubra (ruby leaf creeper)
  • Hibiscus manihot (sunset hibiscus)
  • Colocasia (taro)
  • Hydrocleys commersoni (water poppy)
  • Cyperus giganteus (Mexican papyrus)
  • Nymphoides geminata (chocolate fringe)
  • Cyperus haspen viviparous (dwarf papyrus)
  • Sagittaria montevidensis (Aztec arrowhead)
  • Cyperus papyrus (Egyptian papyrus)

Most floating plants are also tropical. The most popular are Eichhornia crassipes (aka water hyacinth) and Pistia stratoides (aka water lettuce). Due to their high light and water temperature requirements, it is best to treat them as annuals and remove them from the pond in fall.