Overwintering Pond Plants – Part I

How do you winterize pond plants? Pond plants seem to be segregated into their own little class of plants, but they are not all that different from regular plants. Non-hardy garden plants need protection in winter and so do non-hardy pond plants. The hardy ones in both groups can be mostly left alone.

This is the first of a two part post that will provide detailed information on how to winterize pond plants. This post will provide general information that applies to all pond plants. Part II will provide more detailed information on some specific plants.

Trimming Off Top Growth

Most pond plants go dormant in winter and the top growth dies back just like perennials grown in the ground. It is a good idea to trim, the tops back to just above the crown in late fall and remove the cuttings from the pond. This decreases the amount of organic matter in the pond.

To be honest I don’t bother to do this, with one exception. Once the pond has a solid covering of ice, I go out and cut back the cattails and remove them. I stay drier on the ice than if I did it in fall.

Gardening Zones

There is a lot of talk on the internet about hardy and non-hardy pond plants but none of that makes much sense since the list of hardy plants for someone in zone 5 is different than someone in zone 7. Each plant has a hardiness zone range and that is the important piece of information you need to know.  You will also need to know your own hardiness zone which you can find here: Planting Zones and hardiness Zones.

Any pond plant that is not hardy in your zone should be treated as a non-hardy plant.

If you live in a region that does not get ice on the pond you may still need to take special care with tropical plants.

Pond Depth is Important

Plants that grow in soil survive the winter because there is heat from the center of the earth, moving up through the soil layers until it gets to the top layer. This keeps plants warmer in soil than in air. In fact, for plants to survive the winter in above ground containers they need to be at least 1 zone hardier than plants growing in the soil, because the latter get almost no heat from the soil.

The same is true for ponds. Warmth from deep in the earth moves up into the pond water and keeps the lower levels from freezing. Plants grown in above-ground water features freeze much more quickly than in ponds, because they don’t have a heat source. Shallow ponds may freeze solid in very cold climates even though deeper ponds don’t.

How deep does the pond need to be? That depends on the plant and your climate. This is one reason I suggest using native plants in a pond. If they live in local native ponds, and you plant them at the same depth, they will be fine without doing anything special in winter. For example in zone 5, marsh marigolds grow in very shallow water – ditches really – so they do fine in a very shallow pond. The local water lilies will grow in 1 foot of water, so that is all they need in my zone 5 pond.

Hardiness Zones for Pond Plants

The following list is taken from my book Building Natural Ponds, which has a great section on selecting and growing pond plants.

Hardy Pond Plants

A hardy pond plant is any plant that is hardy in your planting zone. For example, lotus is hardy to zone 5, so it is a hardy pond plant for me. If I lived in zone 4, it would be non-hardy.

If your plants are in pots you can lower them to the bottom of the pond, provided it does not freeze solid. This ensures they never get colder than 32F or 0C, because water never gets colder than this.

If the plants are not in pots, but growing on planting shelves as I recommend, then just leave the plants alone. Provided that you planted them at the right depth, they will be fine.

Some people claim that “certain plants can freeze solid” and survive. This is a myth. If a plant freezes solid it will die. However, plants can take temperatures below freezing and still survive – why is this? Plants have sneaky ways to prevent the water in them from freezing. Some produce extra sugars in fall that act like anti-freeze. This is no different that the windshield water in your car. The tubers of these plants can be encased in ice and not freeze solid.

Some of the plants in this super hardy list include iris, sweet flag, rushes, grasses, marsh marigold and horsetails.

Non-hardy Pond Plants

This group includes any plant that is not hardy in your zone, and for most of you, this includes most tropical plants. The treatment for these plants depends on your climate. for more details see Overwintering Pond Plants – Part 2

No Ice on the Pond

Lets first discuss the case where you do not get ice on your pond. You might think all plants would be OK in such a pond, but remember a pond can get down to 32F (0C) and show no ice. Most tropical plants can’t take such cold conditions.

These plants need to be moved indoors before the temperature in the pond gets too low. How low is too low? Each plant will be different but as a general rule of thumb most plants can survive a night temperature of 50F (10C). Many plants can go down to 41F (5C).

It is the water temperature that is important for any plant that has its crown submersed in water. Cold air may damage foliage, but if the water stays above 50F it will survive.

Ice on the pond

If ice forms on the pond you have to worry about both low temperatures as well as ice damaging the crown of the plant.

Tropicals need to be treated as described in the above section. Other non-hardy plants can be handled in one of two ways. You can sink them lower in the pond so they never freeze, or take them inside. Provided they don’t freeze they should survive the winter. If you are not certain about the hardiness of a particular plant, never let it go below 41F (5C).

Hibernation Indoors

Plants that are brought indoors can be treated in one of two general ways; keep them alive and growing, or let them go dormant. The method you select depends on your facilities and the plant itself.

Keep Them Green

This is the best option for many tropical plants because in nature they grow all year round. Genetically they are not been conditioned to go dormant.

If you keep them well watered and provide enough light, these plants can be grown just like house plants and then in spring they can be returned to the pond. Providing water is usually not a problem, but for some of these plants, it is difficult to provide the high light levels they need.

Water lettuce and water hyacinth are two good examples of plants that need relatively high light when grown indoors and for this reason it is difficult to keep these in the house. They are also not that expensive so most people just add them to the compost pile in fall and buy new ones in spring. Or better yet, don’t use these in your pond.

Some examples of tropical plants that do well as houseplants include. umbrella palm, dwarf papyrus, little giant papyrus and white arum lilies.

Keep Them Dormant

This is a good option for many plants. It does not require high light levels, and maintenance during the winter is easy. In general, let the plant go dormant in fall by leaving it in the pond as temperatures drop. Then before a heavy frost, remove leaves and stems, bring them indoors and put them into some storage material. Peat moss works for many plants, but some need to be kept wetter or even submersed in water. The plants are then kept dark and at about 41F (5C) for the winter.

The goal here is to force them to go dormant, and then keep them dormant all winter. In spring you start warming them up, and encourage new growth.

Go Native

If all of the above sounds confusing and a lot of work, then follow my example and go native. I only grow hardy plants in my pond and most are native plants. I don’t have to worry about winterizing them.

My one exception are elephant ears. I have a current obsession with them.