This section is from the book "The Gardener's Monthly And Horticulturist V20", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
I much doubt if there is another plant in cultivation so widely spoken of as the Verbena, yet there are but few who thoroughly understand the nature of this plant. Some gardeners attempt to grow it at a temperature ranging from 40° to 45°, which is entirely too cold; others think they can grow the same plant in the greenhouse where there are Dracaena, Palms, Crotons, etc, at a temperature ranging from 70° to 75°, which is entirely too warm. My experience with the Verbena for the past fifteen years induces me to write as follows: I would make the starting point the first of March, at that date taking cuttings from clean, healthy plants; see that they are in a proper condition. If the stock plants were growing in a temperature ranging from 55° to 60°, which in my opinion is the proper temperature to grow the Verbena, cutting of such plants would be just the style required by cutting them off at or below the third joint. They would root in eight or ten days sufficiently to be potted off in two and a half inch pots, and will make fine, healthy plants by the first of April. At that date they require to be transferred into three-inch pots, at the same time pinching the tops of each plant; it will cause them to strike out with greater vigor, and enable them to become fine, thrifty plants to be set out in the open ground by the first of May. By the middle of August they will have spread to a distance of three, feet; at that date they are covered with flowers and seed pods.
This profuse flowering and seeding somewhat lessens the vitality of the plants and puts them in a weak condition; and should they be left in this exhausted state they would very soon receive the disease which so affects this plant, known as black rust; and now there must be something done to prevent this disease from putting in an appearance, and regain the vitality of the plants. I know of no better method than to cut back the extremities of the shoots some eight inches, and loosen the soil around the plants and in between each layer, by means of a pointed stick or iron. Then adding one gallon of manure water to each plant once a week. Should this liquid be inconvenient. guano would answer the same purpose by adding one pound and a half to twenty gallons of water. This mixture will be sufficiently strong for a single watering each week, and continue this operation until the plants produce a clean and healthy growth, which by the middle of October will give just the style of cutting that is required. Now the propogation begins. I may here state that great importance is attached to the necessity of taking off the cuttings immediately after rain, as the moist weather refreshes the young growth and puts them in a proper condition to be taken off at, or below, the third joint.
Cuttings should be potted immediately on being rooted, not allowing the roots to become larger than a half inch. On potting the cuttings they are placed in the greenhouse and shaded for three or four days, or as long as the condition of the weather may require. As soon as they have struck root in the soil of the pots, they should be sprinkled with sulphur water by adding one pound to ten gallons of water; one watering each week will be sufficient to keep them clean and healthy; fumigate with tobacco two or three times each week, and there is no doubt whatever of having a healthy and vigorous stock; provided proper attention has been given to temperature, watering and fumigation by tobacco.