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Seasonal Pond Care: Why and How to Repot Pond Plants
Veterinary & Aquatic Services Department, Drs. Foster & Smith
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Garden pond in bloomDays are growing longer. Your pond is about to come back to life. And now is the best time to prepare your pond and aquatic plants for a beautiful spring.

Most aquatic plants grow aggressively, and throughout last summer and fall your plants may have grown beyond the limits of their containers. Overgrown plants will gradually decline, and may eventually choke themselves to death. Repotting plants is easy and can be quite rewarding. By providing your plants room to grow, they will absorb more food from the natural nutrients in the pond and the fertilizers you provide. They will also grow lush and reward you with more blooms.

Early spring is a good time to repot plants

The best time to repot pond plants and minimize shock is now, before their explosion of spring growth. Over winter, your plants have been submerged deep in your pond, or cared for indoors. Before returning them to their summer positions, take the time to inspect them. Make sure each plant has room to grow. If the plant's roots have become too crowded in the container, or have grown far out of the drain holes, it is time to divide.

Start with the right tools

Repotting is not difficult, but can be messy. Before you begin, you will want to gather some basic potting tools, a garden hose and bucket, gloves, and, if your pond is large or deep, waders.

  • Aqua gloves and basketsAqua gloves: A must-have if you need to reach deep into cold water. These long, PVC gloves keep your arms and hands dry.

  • Aquatic potting soil: Bog plants and lilies will thrive in organically rich soil, but lotus plants prefer clay. Convenient clay-based aquatic plant soils will work well for most all plants. They are easy to work with, do not stick to your hands, and retain nutrients for your plants.

  • Baskets: Have on hand at least as many new empty baskets as you have plants in your pond. Some plants may not need to be divided, but others may need to be split up into three or four baskets.

  • Cutting tools: Standard garden tools will work with your aquatic plants. You will find a hand trowel and pruning shears especially handy.

  • Fertilizer tablets: Now is a good time to add fertilizer tablets to all of your plants. Depending on the size of your plants, and following manufacturer's recommendations, you will likely need three or four tablets per pot, so get a generous supply. Because it is recommended that you add plant food tablets to each pot monthly, spring through fall, none will go to waste. Nitrate and phosphate-free liquid supplements can also be used to stimulate and feed plants.

  • Green plastic stakes and poly twine: It is not too soon to provide support for climbing plants. Waterproof plastic stakes and twine will hold up all season.

  • Waders: The air may be warm, but your pond water may be under 50°F. If you need to move about in your pond in spring or fall, waders are indispensable.

Repotting methods vary with plant type

Bog cattail plantBog plants: Take the plant gently out of its container and rinse it with a hose to remove all soil. Look for divisions between individual plant stalks and its root system. Pull the divisions apart by hand, or cut them apart with sharp pruning shears or a long, sharp knife. Place a base of soil in the basket until the crown - the part of the plant that should be at "ground" or surface level - rests about an inch below the edge of the basket. Add fertilizer tablets, spaced as recommended, and then fill soil around the plant up to an inch of the crown. Then fill the last inch with lava rock or small river rock up to crown. This will keep loose soil from floating up as you lower the plant to its shelf.

Hint: Some plants, such as cattails, have such a thick growth of roots that it is very difficult to locate sections. For these, just choose small groups of stalks and cut the roots to separate them. Because cattails grow aggressively, you might prefer to place them in a closed pot without holes to keep their roots from taking over in your pond.

Lily padsLilies: Gently lift the lily from its container and rinse it to remove the soil. You will see one large piece, a central taproot. Likely attached to this taproot you will also see secondary roots or "knobs" with their own developing roots. If the knobs can be easily broken free from the core by hand, they are ready for individual planting. However, if the knob cannot easily be broken away, leave it in place. When repotting your "baby" lilies, put about 3-5 inches of soil in the bottom of the basket, then place the shoot so its roots face the bottom and the pad shoots face the top. Surround the shoot with the recommended number of fertilizer tablets. Gently hold the roots down, leaving the shoots up, and add soil around edges until the tip and shoots remain slightly exposed. Add a layer of small rocks to hold the soil in place when set into your pond.

Lotus plantLotus plants: Known for its aggressive growth, lotus may need to be repotted more often than other pond plants. Because the new growth of lotus is very sensitive, it must be handled gently to avoid damaging new shoots. It is more difficult to determine from surface observation when a lotus needs repotting. If you have had the plant more than one year, or you observed that it did not bloom well last season, it is likely ready. Gently pour out as much dirt as you can out of the container. Do not pull on the plant! Then gently rinse the soil away. You should find white tubers with hairy roots on the ends. Healthy tubers will be white to gray in color, and very firm. Others may be in decay. If the tuber is dark or soft, remove it or cut away the decaying portion. Leaving a decaying tuber adjacent to a healthy one can make the healthy one rot. Select a sturdy, solid round container, at least 18" or more across, and 6-8 inches deep. Place a 3" layer of clay or aquatic plant soil in the bottom of the container. Gently hold the lotus in place as you add soil to about one inch over the top of the tuber. Use one hand to put in soil, and the other to protect the sensitive shoots from damage. Place a medium size rock over the center of the tuber, small enough to avoid touching the new growth. Add additional small rocks to keep the soil in place, carefully avoiding the new shoots.

Keep your koi at bay

Lotus and lily plants need protection from fish, especially koi. Larger rocks, 3-5", placed over the roots will help prevent your fish from rooting them up. You can also cut a hole in the center of the fine mesh of an AquaPlanter and place it over the top of the container to protect roots. Once they are big enough to hold leaves above the water, the stems of the lotus are prickly and should hold up to koi. Lily leaves, however, can be a favorite season-long snack. To keep koi from eating your expensive and beautiful lilies, provide them an economical plant they prefer, water hyacinths.

Clean up tip

The residues from submerged plants are often black and gooey, and a bit smelly. For the protection of your fish, do not place your hands in your pond water again until soaps or hand cleaners are thoroughly rinsed away.

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