Winterizing agapanthus

Bob Dluzen
Special to The Detroit News

 We have a couple large pots of agapanthus plants, also called Lily of the Nile, that have been with us for nearly 30 years.

Each summer the potted plants produce azure-blue, loose globes of flowers suspended above its leaves on tall stalks. Even when the plant is not flowering, the foliage itself is attractive and makes a nice filler of green when used as part of an outdoor potted arrangement.

These plants are not very demanding compared to some of the flowering plants we grow at our house.

The foliage on our agapanthus stays green all winter even though it is in a dormant condition. After exposure to temperatures in the mid-twenties, the leaves show a bit of cold damage here and there and they are not as upright as during the growing season.

Although its common name is Lily of the Nile, it originates from the opposite end of the African continent, way down in Southern Africa. In its native environment the wild species is hardy in areas equivalent to our zones 8-11 or so. Some newer hybrids however are tolerant to much colder temperatures.

Ours was passed along to us from a retiring horticulturist and is such an old cultivar that we don’t know its variety name, if it even ever had one. So not knowing its ancient history, we assume it’s not winter hardy and treat the plants as a tender perennial, which means we make sure to bring it in every fall to protect it from the winter. I suppose I could divide the potted cluster and plant some in the ground outside and see how they do over winter, that is if I really wanted to find out if it’s a hardy variety.

Through the years we have overwintered them a couple of different ways. When the plants were much younger, they spent their winters in a warm greenhouse staying active all year-round and did quite well, as you would expect from a semi-tropical plant.

In more recent years, I found out they are perfectly happy being dormant during the winter in a cool, somewhat dry spot out of direct sunlight. The long winter’s rest seems to do them good and they’re always eager to begin growing when spring arrives.

The spot I’ve been using for them for the past 10  years or so is right up against the container of one of my citrus trees. My citrus trees come in for winter, too, of course. The tree canopy gets sunlight from a south facing window but underneath, only indirect filtered light reaches the agapanthus.

The temperature in that spot during the coldest months is around 45 to 50 degrees. Under those conditions, very little photosynthesis is taking place. The only water they get is just enough to keep the soil from drying out completely through evaporation. The citrus trees need more water, so it’s easy enough to check the agapanthus every time I water the trees. It’s not very often the agapanthus need water.

Before bringing them in in the fall, I like to allow them to be exposed to light frost. The frost does not damage the plant but it seems to send a signal to them that winter will be here soon.

During the growing season, new plants form alongside the mother agapanthus plant forming tight clusters.

Since Lily of the Nile thrives in crowded conditions, it's rare that I’ll divide our pots. The last time I divided one of the pots was several years ago. I potted up some single plants that went to several different people. I’m not sure if they still have the plants or not.

Several varieties of Lily of the Nile have been developed including some white flowering types, tall varieties, short growing, compact varieties, in addition to the aforementioned hardy ones.

Agapanthus are available at garden centers and online.