Southwestern USA
Summers can be blazing, but pleasantly mild winters do offer -

(with tips for over-wintering favorite tropical waterlilies indoors)

by Leo Martin, Phoenix, Arizona


Water gardening challenges vary with different climates. This is the first in a series of water gardening notes from Phoenix, Arizona, where summers are exceptionally hot and dry, and winters mild and dry.

We divide Arizona geographically into (1) the higher-elevation Colorado Plateau in the northeast corner of the state, and (2) the lower-elevation Sonoran Desert that stretches across the border into Sonora and Baja California Norte, Mexico.

The Colorado Plateau has temperatures much like those in the midwestern and northeastern USA, and much of Europe, but less annual rainfall. Flagstaff, the Hopi and Navajo reservations, and the Grand Canyon are up on the Colorado Plateau.

The Sonoran Desert features mostly low-lying plains punctuated by mountain ranges, some lower and some higher. Tucson, Yuma, and the state capital Phoenix lie in the Sonoran Desert. Summers produce more heat than many people can imagine; winters give us pleasant weather, nicer than many people can imagine. Relative humidity stays very low except during the summer rainy season when we have a little more humidity.

Arizona Map from
Map of
Click to enlarge

Phoenix lies at about 1,100 feet / 330 meters elevation. Winter daytime temperatures range between 50-75 F / 10-28C and night temperatures vary around 40-60 F / 5-18C. Any night between November and February might bring a few hours of temperatures down to 20 F / -7C, and every ten years or so a cold snap brings a few nights with temperatures down into the teens F / -10C. With sunrise temperatures always rise well above freezing. I built my pond in 1986 and it has frozen over only once. I have killing frosts almost every year, though.

Tucson sits another 1,000 feet / 300 meters higher than Phoenix and has a somewhat cooler clilmate. Snow falls in the Catalina Mountains at the northern city limits of Tucson almost every year, but rarely in Tucson.

Hardy waterlilies grow just fine here without special winter care. They come out of dormancy in March or April and bloom from April until October. Their leaves are finished by November. The only difficulty with hardies is keeping them from overgrowing the pond.

Tropical lilies usually survive the winter in the pond and return the following spring. They continue to grow and bloom as the weather cools, though they really slow down. Blue-flowered plants, especially, may bloom until hit by a heavy frost. In warm winters when we have no frost at all, tropical waterlilies may flower outside all winter.

Overwintering Tropicals in the Sunroom

Every now and then a tropical lily doesn't return in the spring. So, I've learned to overwinter several of my favorite tropicals in my sunroom, in a bucket. This works easiest with tubers. I find that water temperatures around 70 F / 21 C work well.

First: Safety! Water and electricity can be dangerous. For maximum safety, plug all electrical equipment near water into a socket with a ground-fault circuit interrupter. Unplug all electrical equipment before reaching into the water. Never remove a warm heater from the water or it may break instantly. Always unplug the heater and wait a half hour or more to equilibrate with the water temperature before removing the heater from the water.

Location: Select a spot with at least a few hours' direct sun. Remember, when working with water you will certainly spill some, so the piano top or an expensive silk rug is probably not a good spot for a water garden. The warmer the air temperature stays in your lily spa, the easier it is to keep the water warm.

Materials: Make use of a clean 5-gallon (20-liter) bucket. I use well-rinsed laundry degergent buckets; they seem sturdier than paint buckets. Besides, I wash laundry more often than I repaint my house. The orange buckets sold at the local big-box home store seem too flimsy to me.

Heater: Use a fully-submersible submersible aquarium heater: Don't get the design that attaches to the top of an aquarium; heated water evaporates fast. The heat output you buy depends on where you place your bucket. A low-watt heater designed for a 5-gallon / 20 liter tank may only raise the water in your bucket by 10 degrees F / 5.5 degrees C. If your growing area gets very cold at night, this will not be warm enough to keep your lilies happy. My sunroom stays quite warm in the daytime, but often dips down to 40 F / 4C at night. A heater designed for a 50-gallon / 200 liter tank costs only about twice as much as the 5-gallon heater. I bought one designed for a 50-gallon tank to use in my 5-gallon bucket.

Extension cord: You might need one.

Thermometer: Ditto. I test the water temperature with my hand. It should be barely lukewarm, not hot and not cool.

Procedure: Fill the bucket with water and place it where it receives at least about five hours of direct sun. I think artificial lighting would work fine, though I don't need it.

Place the heater into the water. Be sure to submerge it completely. Plug in the heater. Remember to keep all electrical connections above the water level so water cannot flow down the cord and wet the electric socket or a cord-to-cord connection. You should see the heater light come on.

Return after a few hours. Unplug the heater. Check the water temperature. Do not put your hand into water containing a heater that is connected to the wall socket. If you are really diligent, come back at night and re-check the water temperature. Adjust the heater thermostat as necessary. Regulate the water temperature before adding your tubers to avoid having cooked tubers.

When you are satisfied with the water temperature, add your labeled tubers. Just let them float or sink in the water. Use plastic mesh bags to hold the tubers when I have more than one variety. This way you can more easily keep them properly labeled. Your goal is to get them through the winter alive, but not alive and growing. If they do begin growing, that is not really a problem; but you probably don't have much room in your bucket. If your tubers begin to grow, turn down the water temperature a little.Check the water level every few days. If the water level drops far enough to expose the heater, it breaks. A submerged, live, broken heater creates a very dangerous situation.

If you experience a mosquito problem, put a drop of dish soap in the water. This breaks the surface tension of the water and the larvae drown. (This works in your tank bromeliads, by the way!)

Change the water every month or so to prevent salt buildup. Again, be sure to unplug the heater and let it cool down before removing it from the water.

In the spring, turn up the water temperature bit by bit until it becomes really warm and the tubers begin sprouting. Nip off plantlets, pot them into small pots, and let them enjoy a head start in the bucket before setting them outside. You may see flowers earlier than usual this way.

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