This section is from the book "The Florists' Manual", by William Scott. Also available from Amazon: The Florist's Manual.
This plant is often called arum lily, but with us is universally called the calla lily. For many years it was a most important plant with us and today there are a number of people who prefer them to the true lilies. They are of the easiest growth, if you remember one important thing, and that is that the calla comes from northern Africa, and does not want to be starved in a cool greenhouse.
There are several ways of growing them. To begin with, they propagate easily from offsets, which you can take off when repotting the plants in the fall. Some plant them out, but if they have much root room they grow too rampant and the flowers are too large to be useful.
In early May our houses are too crowded to keep the callas on the bench, and they are taken outside and laid down where they can be covered in case of a sharp frost. The top withers away and for a few months the root is dry. In August we shake off all the soil and start them growing again in 5-inch or 6-inch pots, keeping them in a frame as long as there is no danger of frost, and in winter give them a light house where it is not less than 60 degrees at night. Although almost an aquatic, the soil should be in such condition that water passes through it freely. For soil use three-fourths of coarse loam and one-fourth of decomposed cow manure. They want lots of syringing and fumigating, for thrips and red spider trouble the leaves.
If you want to raise some specimens that will require a 9-inch or 10-inch pot and bear three or four flowers at one time, select some of your strongest plants in May and plant them out two or three feet apart in a deep, rich soil, where you can water them copiously in dry times. They lift easily at the end of September and will make great plants.
The small offsets or bulblets that come off the corm in August can be potted in 2-inch pots and grown on. They can be kept during the winter in 3-inch pots and in May shifted into 5inch and plunged in a frame. They want a copious supply of water during summer. It is remarkable the strong flowering plants you will get from these little bulblets in a few months. As previously said, the calla, when planted out and given liberal space for root growth, is inclined to grow very strong and give few flowers in the dark days. In the bright days of spring you will get lots of flowers from these beds, but the flowers are often of unwieldy size. Growing a good strong corm in a 6-inch or 7-inch pot during winter in a bright, warm house will be found as practical and profitable as any method.
The calla tubers will bear resting or allowing the soil in pots or beds to become perfectly dry. Those grown in pots are usually placed outside in June on their sides so that the soil may become dry. The top withers and they are kept in this state till early September, when they should be shaken out, given new soil and started growing, and will soon flower. For this seemingly unnatural rest they are not in the least any the worse in health or vigor.
Richardia albo-maculata has a small, greenish-white flower and a prettily spotted leaf, which we used to use in our veranda-boxes. It rests in winter and the corm should be started growing in February. To increase your stock of this the corm can be cut in two or three pieces and started growing in February. Keep rather dry till leaf growth begins. In June plant them out, lift in fall and store in dry soil till time to start again.
There is a magnificent yellow calla; it is R. Elliottiana. In size and form it is like the common calla, but the leaves are spotted and not so thick in texture. The flower is simply grand. I don't know when I have seen a flower that pleased me so much. Fancy a dozen or more of these flowers in a vase; what can be richer? It is not yet common or we would see and hear more of it, but every florist should obtain a stock of it.
A single corm was given to me several years ago by the late George Savage, of Rochester, with the advice to start it in sand and give little water till growth began. This was good advice, for the following June it threw up a gorgeous bloom. They should be dormant in the soil during winter and shaken out and started in early spring. We divided this corm into four or five pieces with success, one of which flowered the following spring. This is such a magnificent flower I cannot praise it too highly.