Starting Seeds under Lights

I grow Clivia in central Indiana (USA). This is in the Midwest, between the Great Lakes to the north and the Ohio River to the south. We have hot summers and cold winters: usual afternoon high temperatures in summer are 86°F (about 30°C) and this past summer our afternoons exceeded 90°F (32°C) on more than thirty days. Our hottest days do not exceed 100°F (about 38°C). In winter, we have several snowfalls each year, and our lowest morning temperatures vary from +6°F (-14°C) to -20°F (-28°C) in our occasional very cold spells. This is U.S. Department of Agriculture cold hardiness zone.

This is not a place where clivias are garden plants. They absolutely have to be protected indoors or in a greenhouse over winter. In summer, they do very well outdoors, so long as they are in medium to heavy dappled shade. I grow my mature clivias outdoors in summer in our lath house, and in a home greenhouse in winter.

Clivia seeds tend to ripen around Christmas time here in Indiana, just as winter is getting a good start. That means we start them indoors during winter, along with Nerine and Haemanthus and other later-ripening seeds. While a sunny window would be a possibility, and we do have a couple of home greenhouses, neither works well for us. The sunny windowsill is a shortcut for the cat, and gets too hot on sunny days. The greenhouses are really too cool in winter for optimal starting of Clivia seeds. The most satisfactory alternative that I have found is to start them indoors under fluorescent lights.

Clivia seeds kept too warm will dry out rather than germinate. Left too cold, they simply wait for nicer temperatures. I have arrived at a working temperature range for Clivia germination that seems to be satisfactory: warmer than 65°F but no warmer than 80°F (about 18°C to 26 or 27°C). I keep the young Clivia seedlings under the lights and in this temperature range for about six months. Generally, it is summer by then, and they can be moved outdoors into our lath house (probably 60 to 70% shade) for the summer.

I use a mixture of PromixT and sand in a ratio of 2 parts Promix to 1 part sand by volume. PromixT is a peat-based soil-free potting mix containing perlite and vermiculite in addition to the peat. It also shows quite a few small twigs and bits of sticks, and I suspect that there is also some fine charcoal added to it.

I plant all my especially prized seeds, one seed to a pot, in 5½ inch (about 14 cm) square by 5½ inch deep plastic pots. The seed is pressed into the surface of the potting mix, and then the pot is stood in a bucket of water to thoroughly wet all the potting soil clear to the surface. The well-wetted pot is finally set in a tray with other pots of the same lot, and the whole is moved into the light room and placed under the fluorescent lights. Initially the lights may be as low as a few inches above the seeds. As the leaves grow, the lights are raised to stay above the leaves for as long as possible.

If you want to start hundreds or thousands of clivias from seed at one time, this approach needs to be modified. Plant the seeds from a single batch in a larger community container, such as a polystyrene foam box or tray. It should be at least 5 inches deep, and must have plenty of drainage holes in the bottom.

As we have come to grow more and more clivias and bulbs from seed, I have had to have a wall full of shelves installed for the plant lights. They are in my computer room, which stays a bit warmer than the rest of the house all year around. There are four shelves mounted on one wall. Each shelf is 22½ inches deep (about 57 cm) by 9 ft 10½ inches long (about 3 meters), made of ½ inch plywood and supported by 2 inch x 4 inch lumber. The vertical spacing between shelves is about 22½ inches. The shelves and the walls behind them and at the ends were painted with a matt white enamel latex paint to maximize light efficiency. Each shelf is illuminated by two pairs of two-tube 40-watt fluorescent tubes in shop light fixtures, for a total of eight 40-watt tubes per shelf. Each fixture is hung on chains so their heights can be adjusted as needed. Each shelf offers 18.5 square feet of space, for a total of 74 square feet (about 6.8 sq. meters) under these lights.

Pots are placed in plastic trays on the shelves under the lights. The pots are watered from below, by pouring water into the trays, to avoid washing the seeds loose from the potting medium. Fungus gnats may become a problem, and can be controlled by sprinkling granules of Marathon® on the surface and watering into the soil. The insecticide is watered into the soil by gently watering the pot from above. Marathon® contains 1% imidacloprid as the active agent. It is manufactured by Olympic Horticultural Products for the greenhouse and nursery trade in the USA.

Growing seedlings on

As Clivia seedlings in containers grow, they produce more and more roots. When the roots begin to fill the pot or to grow out through the drainage holes in the bottom of the pot, it is time to move the plant into a larger pot. It is critical to the development of the young plant that it be able to produce as many healthy roots as possible.

When the seedling is moved to a larger container, it is also time to change from the sandy, peat, starting medium to a more sharply draining mix. Some growers recommend using orchid potting mixes for growing Clivia plants, but I have not tried that yet. I have been using a gritty mix with reasonable success. The composition is roughly PromixT, plus sand, plus granite chick starter grit (about 1/8 in mesh, or 3 mm) in a ratio of 2 parts Promix to 1 part sand to 1 part granite grit by volume. The components are mixed dry in a small concrete mixer until well mixed, or up to an hour. Promix is a commercial soil-less peat-based potting mixture, produced in Canada.

The seedling is removed from its original pot and as much as possible of the original growing medium is shaken gently off the roots. Be careful not to damage the roots. The next step is to re-pot in a slightly larger container. If the seedling had been growing in a 5½-inch (about 14 cm) square pot, you can plant it in a 1-gallon container about 6½ inches (16 or 17 cm) in diameter and 6½ inches deep. Plug the drainage holes loosely with a bit of sphagnum moss, and work the gritty mix carefully in among the roots. At this point, I usually pot the crown of the seedling slightly above the surface of the potting mix in the new pot.

Until the young Clivia plants reach a size such that they are capable of blooming, they have no need for a dry or cool rest period in winter. I try to keep the one- and the two-year old plants growing actively through the entire winter. The two-year olds are all in the greenhouse, while some of the one-year old plants are still under lights and the rest in the greenhouse. Keep the greenhouse warm, at about 60°F, at least, and use supplemental lighting if necessary. I have two 400-watt high intensity metal halide lamps hung above one bench in my lean-to greenhouse, but I am not currently using them. Except during the coldest periods (cold inside the greenhouse, that is), water and feed the young plants regularly with a very dilute solution of soluble plant food. I recommend using Peters 20-20-20 soluble with trace elements, at about ¼ to ½ level teaspoonful (about 5 ml) per gallon (about 1.5 to 3 grams in 4 liters.)

When using a continuous feeding regimen such as this, it is necessary to water to excess at each watering, so the accumulating salts are regularly flushed out the bottom of the pot. This is another reason that a quick-draining growing medium is advisable.

My aim is to grow large, healthy seedlings to blooming size in 30 months. I do not always achieve this, but a significant fraction of the seedling plants I have grown so far have bloomed in 30 to 36 months. I do this in a relatively harsh climate, using my own home, a lath house, and a glass and aluminum lean-to home greenhouse. I am not ever going to keep the Belgian Clivia growers awake at night with worry!

Jim Shields
© Copyright 2002 by James E. Shields. Used with permission.