This section is from the book "The Gardener's Monthly And Horticulturist V22", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
As many florists in the culture of Primroses, and parties growing them for their own use, fail in their cultivation, it may be of importance to point out some of the causes. In many cases the seeds are worthless, being gathered before fully matured, or are injured in transit across the ocean. On account of this, and the high prices at which these seeds are usually sold, amateurs and many skilled florists, hesitate to venture in their culture. Many failures can be traced to having the plants too wet when once sprouted, or to being placed in a damp or too moist a situation. In this condition the young plants will damp off, or, if they survive, will make only a slender and sickly growth.
One of the most general mistakes is in placing the plants in too warm a location, and another in not giving sufficient light.
In following the directions given below, Chinese Primroses can be brought to a high state of perfection, and no danger of failure need be feared.
The soil for Primroses must be of the richest quality. Woods mold, muck, or sods well decayed, and about one-third sand, with a liberal supply of well rotted stable manure, is well suited for Primroses. Where this cannot be had, chip dirt, or any rich garden soil mixed with good manure, will do very well. The soil should be prepared at once, and kept out doors until there is danger of winter setting in, when it should be removed to the cellar. When wanted for use it should be finely pulverized and sifted, as the roots of the Primroses are all very fine and tender. They cannot penetrate hard lumps of earth. The seed should be sown either in shallow seed-pans or small shallow boxes, filled about two inches with finely pulverized earth and sand. Sow the seeds thinly on this, press with the bottom of a small flower pot, and cover evenly about one-sixteenth to one-eighth of an inch; smooth off and press the earth down again: now cover quite thinly with moss. If no moss is at hand, small blades of fine grass or old muslin will do, merely to keep the earth from drying out. Water at once with a fine rose sprinkler.
This watering will in most instances be all that will be needed until the seeds are sprouted, though they must be looked after every day, and when the earth gets dry a light sprinkling given them. Set the boxes or pans in a cool place, and where the winds cannot reach them. As soon as the young plants make their appearance, the moss or other covering should be carefully removed. The earth during the day must be moist until they are fairly established; but care must now be taken in giving the proper supply of water; for if the earth should become very wet, the small plants will damp off, particularly if too wet during the night or in cloudy weather. It is safer never to water in the evening, even when the top soil is dry.
The boxes or pans may be covered with glass when no moss is used; but this requires careful watching, and considerable skill in their proper and safe management; for when the earth once becomes too much water-soaked, and remains so for a day or two at the time the seeds are sprouting, they will be all ruined. The glass should be lifted off occasionally, and the box placed in the sun for a short time. As soon as the young plants make their appearance, the glass should be taken off, except during the hottest part of the day.
The seed should be sown about the 1st, or not later than the 15th of July. The plants will then commence to bloom in the beginning of December, and continue in perfect flower until spring. If started earlier the flowers will not be so fine during the latter part of the winter, at the time when flowers are most appreciated.
About the middle of August, if the young plants have made good growth and strong roots, they should be transplanted into small pots (the smallest size), using the soil described above, pulverized and sifted. As soon as they are planted into these pots, give a pretty thorough watering and shade for a few days, then set the pots where there is plenty of light, not in the sun, and in a dry and as cool a place as can be found at this season of the year; by this treatment they will grow stocky and produce large and bright colored flowers. It is safest in all the stages of growth to be fearful of giving too much water rather than too little. The earth should become very dry occasionally, even to the extent that the foliage begins to wilt. This is rather a benefit and in nowise an injury. Then give a copious supply of water, completely saturating all the earth in the pot; this will start the plants into new life and fresh vigor, and will keep them in a healthy condition, and prepare them for a much finer bloom than when kept wet at all times. The foliage should be frequently sprinkled, particularly the under sides of the leaves, to keep off the red spider.
This should be continued until they commence blooming, but no water should be allowed on the flowers.
As soon as these small pots are filled with the roots, the plants must be shifted into other pots one size larger (3-inch). Do not disturb the roots in shifting from one pot into another; they are very small and are easily broken. Now give them water, and treat them as you did when in the small pots. When these pots become filled with roots, which can be seen by the lower leaves turning brown, they must be turned into larger pots. The lower leaves should now be cut off, and a small portion of the roots at the bottom of the pot may also be scraped off, and the plants set deeper than they stood before. For this planting use a four-inch pot. About this time the flower buds appear, and they seldom require larger pots the first season, though if the roots should become too much packed in the pots, and the lower leaves turn yellow, they must be planted into five-inch pots, or they will lose their vigor and produce smaller flowers.
At the time they are turned into the four-inch pots, or earlier, say 1st of November, they should be set in the place where they are wanted when in bloom; they then become adapted to the place, and will do very much better during the winter than when a new place is given them after they are in full bloom. When set on a window always put the Primroses next the glass. They thrive best in a cool place and a full share of light.
To keep Primroses over the summer, place the pots in a frame or under a tree; will need little attention during the summer. About the 1st of September take them out of the pots and cut nearly all the roots off, also the leaves: plant into smaller sized pots, and start them into growth; later shift them into four or five-inch pots. The flowers are seldom as fine and large as they are on young plants.