Winter Pond Care

Special Considerations for End of Season Care

pond plants

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 with 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.

Plant Care

There are three main categories of pond plants: hardy, semi-tropical, and tropical.

Hardy plants are those that will winter over in your pond without any special care required, then will regrow in the spring. The majority of plants we sell fall into this category, including hardy waterlilies. Hardy waterlilies will winter over as long as their crown does not freeze. In our Willamette Valley climate, a depth of 18-24” is usually sufficient. There are a few hardy plants that require some protection. These include Saururus cernuus: Lizard’s Tail and Pontaderia cordata: Pickerel. These varieties 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.

Semi-tropical plants are those that will winter over 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.

Semi-tropical plants are those that will winter over 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. The following is a list of semi-tropical plants:

  • Canna sp.
  • Cyperus alternifolius: Umbrella Palm
  • Hedychium coronarium: Butterfly Ginger
  • Ruellia brittoniana: Bluebell

Tropical water plants don’t go dormant in the winter. For this reason, they require a protected environment such as a heated greenhouse where they can receive necessary warmth and light to continue growing. Many tropical plants can also make good houseplants through the winter given the right conditions including water and light.

  • 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
  • Wedelia trilobata: Water Zinnia

Most floating plants are also tropical. The most popular are Eichhornia crassipes (Water Hyacinth) and Pistia stratoides (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.

If you did not see a particular plant that you purchased on this list, chances are good that it is hardy and will go dormant for the winter before reappearing in the spring.


You may choose to remove your pump prior to cold weather, but in our mild climate, you can enjoy water features year around. In 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.

Cyperus: Papyrus

A varied selection of plants has impact not only on the beauty of a pond but also on the water quality. There are four basic types of pond plants. For an attractive, well-balanced pond, we recommend using a mixture of all four types. These recommendations are for shady ponds with at least three hours of direct sunlight each day. While some of these plants may grow with even less sunlight, they may not flower.

Lists of the four areas of Plants for Shady Ponds are in the tabs below and can also be downloaded here.

Download the full article on Shady Pond Plants.

Water Lettuce (Frog not included)

These plants float freely on the water surface and reduce algae by competing for nutrients, shading the water to cool it and lowering the light penetration. Most floaters are tropical and those should be removed from the pond and composted prior to the onset of winter.

  • Azolla Miniature: Water Fern
  • Hydrocharis morus-ranae: Frogbit
  • Pistia stratoides: Water Lettuce*

water lily

These plants root on the bottom of the pond and send floating leaves up to the surface. Everyone’s favorite pond plant, the Waterlily, is in this group.

  • Hydrocleys commersoni: Water Poppy*
  • Marsilea mutica: Water Clover
  • Nymphaea sp.: & hybrids
  • Hardy Water Lilies (selected varieties)
    • Red: Attraction, Chas. de Meurville, Gloriosa, James Brydon, Lucida
    • Pink: Fabiola, Masaniello, Rose Laydekeri
    • White: Gladstone, Hal Miller, Hermine
    • Yellow: Charlene Strawn, Chromatella, Helvola, Joey Tomocik, Texas Dawn
    • Changeable: Chrysantha, Commanche, Graziella
  • Nymphaea sp.: & hybrids
  • Tropical Water Lilies (selected varieties)*
  • Nymphoides crenata: Yellow-fringed Snowflake

Ceratophyllum demersum: Hornwort


This group of plants grows beneath the surface of the water where most or all of their foliage remains. The term “oxygenators” is used because they release oxygen into the water during the day. The primary function of these plants is to remove excess nutrients from the pond, thereby reducing the growth of algae. They also provide spawning areas and protective cover for fish. Most of these plants are grassy in form and are sold in tied bunches.

  • Ceratophyllum demersum: Hornwort
  • Marsilea mutica: Water Clover
  • Myriophyllum aquatica: Parrot’s Feather*
  • Vallisneria americana: Tape Grass

Marsh Marigold

These plants grow in shallow water or saturated soil around the perimeter of ponds or along the banks of streams. They frame the water feature, soften the transition between land and water, and provide an attractive backdrop to small ponds.

  • Acorus sp.: Sweet Flag
  • Calla palustris: Bog Arum
  • Caltha palustris sp.: Marsh Marigold
  • Colocasia sp.: Taro*
  • Cyperus sp: Papyrus*
  • Echinodorus sp.: Radican Sword
  • Equisetum sp.: Horsetail Rush
  • Houttyunia sp.: Houttuynia
  • Iris fulva: Red Iris
  • Iris louisiana: Louisiana Iris
  • Iris versicolor: Versicolor Blue Iris
  • Juncus sp.: Rush
  • Lobelia sp.: Lobelia
  • Marsilea quadrifolia: Upright Water Clover
  • Menyanthes trifoliata: Bog Bean
  • Nasturtium officinale: Water Cress
  • Orontium aquaticum: Golden Club
  • Peltandra virginica: Spoonflower
  • Sagittaria sp.: Arrowhead
  • Saururus sp.: Lizard’s Tail
  • Scirpus albescens: Variegated Bullrush
  • Scirpus zebrinus: Zebra Rush
  • Thalia sp.: Hardy Water Canna
  • Typha latifolia variegata: Variegated Cattail

*Tropical or semi-tropical plants


Probably the most vexing problem encountered by pond owners is the presence of algae. Algae growth is spurred by excessive organic materials, warm stagnant water, and sunlight. Use the following suggestions to keep your water healthy and combat unwanted algae growth:

Keep the pond free of unwanted organic material. Use a net to scoop out leaves and debris. Trim dead foliage off pond plants rather than allowing it to decompose in the water. Do not overfeed fish. Undigested fish food is the primary pollutant in many ponds. Digested fish food is another pollutant, so keep your fish population under control. 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 ultra- violet light, which kills all free-floating algae, you are guaranteed to have crystal clear water.

Keep your pond water pH close to neutral.

High pH is hard on fish and plants, plus it 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 and process 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.

pond plants

The primary ingredient in any recipe for a healthy pond is the addition of lots of pond plants.

Plants work for you to provide an environment of healthy water: they add shade, remove excess nutrients and toxins, and add oxygen to refresh the water.

Spring is when the pond awakens from its long winter dormancy as signs of life reappear with longer days. By spending a little extra time now, the pond will be ready for the upcoming season. A good start is to cut back any dead foliage remaining 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 rebalance the water once the pond is refilled.

Spring is also the time to begin 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.

Download the full article on Pond Care Basics.

Winter Pond Care cont'd

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. Below 50° 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° and under - No food at all
  • 51° to 60° - Once per week
  • 60° to 65° - Every 3-4 days
  • 65° to75° - Once per day
  • 75° to 80° - 2-3 times per day
  • 80° to 85° - Same but increase amount to no more than can be consumed in 5 minutes
  • 85° and higher - Decrease amount due to possible oxygen

Fish and 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 in order to leave a layer of water undisturbed 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 to allow for gas exchange.


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 below 50-60° water temperature. 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 else continuously circulate water through it to prevent freezing and cracking.

Download the full article on Winter Pond Care.

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Water Plants