1. Do you have any tried-and-true advice or handy hints for storing hardy waterlilies over the winter?
There are a couple ways to store hardy waterlilies for the winter. First of all, for both methods you will need to remove the potted waterlily from your pond. Trim all the leaves except the smallest growing tips emerging from the crown, as they are next year’s growth. For the first method, after trimming, add some soil or gravel to completely cover the rhizome. Then sink the pot to the lowest level of the pond and leave it for the winter. If the surface of the pond freezes, keep a hole in it to allow gases to escape. This method only works if your pond does not freeze solid during the winter. If it does freeze solid, it is best to use the next method.
Take the waterlily tuber out of the pot after you finish trimming the leaves. Wash it and trim the roots off as well. Pack the waterlily tuber in a plastic bag in slightly damp peat and store in a basement or other cool, dark area that doesn't freeze, or in a refrigerator. Open the bag once a month to check on the tuber. If the waterlily tuber shows signs of rot it will have to be thrown away. If the peat becomes too wet, repack with fresh peat, and check it again next month.
2. Even among the hardy waterlilies, are there some that are hardier than others?
Absolutely! The yellows are the most notorious for not being truly hardy and with good reason. The yellow waterlilies all have some genes from N. mexicana in them. Because N. mexicana is not a true hardy waterlily this causes its hybrids to be less tolerant of cold temperatures.
3. What is the number one mistake that people make when over-wintering their hardy waterlilies?
I would say that the number one mistake people make is not checking the water garden often enough in the winter. If the pond freezes solid they lose their waterlilies.
4. Is it helpful to use a water heater or a bubbler in the winter?
Water heaters would certainly stop your water from freezing but the cost could be prohibitive. Bubblers can also prevent your water garden pond from freezing because it mixes the warmer water at the bottom with the colder surface water and the movement prevents ice from forming.
5. Now that Spring is starting to arrive, what should the water garden owner do to give their waterlilies the best head start for the new season?
The easiest method is to simply fertilize the waterlily with your favorite fertilizer at the recommended rate. Then bring the pot up to 6 inches from the surface where it will be in the warmer, sun-influenced water. This can be accomplished by supporting the waterlily pot with concrete blocks. As your plant matures you can then submerge it further to your desired depth. If you stored your waterlily tuber in a basement or refrigerator in a bag then you must repot the tuber in fresh soil. Don't forget a layer of gravel on the surface of the soil to help stabilize it. Apply a fresh supply of fertilizer and your plants are off to a great start for the season.
(Just a note: We find that if you over-winter your plants in the pot you get a better response if you repot them in the spring rather than simply fertilizing the existing pot.)
1. For people in cold climates, is it practical to over-winter tropical waterlilies, or is it better to treat them as annuals?
For the most part we recommend that tropical waterlilies be treated like annuals. However, they can be over wintered in cold climates. It's just a bit more work. If you would like to attempt to over-winter them, then here’s what you need to do. Remove the pot from the water garden and remove the tropical waterlily from the soil. Rinse gently to remove any soil. Look closely at the bottom of the plant for a small, dark, round tuber anywhere from the size of a nickel to a fifty-cent piece (There may be more than one.). If a tuber is present, remove it by twisting. Clean the waterlily tuber and you can store it in one of two ways. If you have an aquarium you can place the tuber in a clean aquarium with no substrate. Give it 12 hours of light and heat the water to about 70 degrees. The tropical waterlily tuber will put up small leaves and remain this way until time to plant in the spring. Do not fertilize because you do not want to encourage growth. The other method is to store the tuber in damp, clean sand inside of a jar or bag in a cool area that will not freeze. A basement or refrigerator will work well for this.
2. In your opinion, is it better to try and over-winter the root system of the main plant, or to harvest and over-winter small corms/tubers that will produce new tropical waterlilies?
Although it can be done I don't recommend over-wintering the root system with tropical waterlilies. We find you get a more vigorous plant by starting new plants from a tuber each year.
3. Do some varieties over-winter better than others?
No tropical waterlilies over winter outdoors however some varieties withstand cold better than others (The only exception is south Florida and south Texas). Tropical waterlilies do vary in tolerance to cold temperatures. Most of the viviparous tropical waterlilies are a little more cold tolerant than the rest of the tropicals. We can over-winter many of these types outdoors in south Florida, whereas we can’t with the tuber producing varieties. I know that doesn’t help 99% of water gardeners because of their climate, but it does mean that you will get to enjoy your tropical waterlily a little longer in the northern climates with viviparous plants like Panama Pacific versus non-viviparous varieties like Blue Beauty.
4. After bringing a tropical waterlily out of storage, what should the water garden owner do to give their tropicals the best head start for the new season?
Tropical waterlilies are very sensitive to cold water, especially the small plants. The trick is to pot your tropical waterlily in March in a small pot (4" or so) filled with rich soil topped with sand or gravel, and keep it inside in an aquarium at 70-80 degrees. Grow lights or fluorescent lighting should be used for about 12 hours per day. In this environment the waterlily will reach a decent size and should make the transition outdoors easily. Once the water reaches and maintains 70 degrees it’s time to plant your lily outside. Choose your container size and keep in mind the bigger the container the larger the waterlily will get. Use at least a 3-gallon container and fill with rich heavy potting soil. Apply your favorite fertilizer at the recommended rate. Now transplant your waterlily into the larger pot. Remember, the less you disturb the roots while transplanting the smaller pot to the larger pot, the faster the waterlily will grow. Cover the top of the soil with gravel and submerge the plant to a depth of 6 inches. As the plant matures you can submerge it to a depth of 3 feet or more in your water garden. Remember to fertilize frequently during the growing season because tropical waterlilies are fast growers and consume lots of fertilizer.