All our ornamental shrubs of the lawn and park may be divided into three general classes as to habits of flowering and pruning : (1. Seedling Variations) Those that flower on the same season's growth, such as the rose, hardy hydrangea, privet, mock-orange, and tamarix, should be cut back more or less severely in the dormant season. This cutting back of the new growth, and in some cases still lower, increases the number of new shoots on which the flowers appear. In the North and Northwest, where the best hybrid roses and such shrubs as Spirœa callosa are not hardy in open exposure, the winter covering is easier when severely cut back to prepare for blooming the next summer. In milder climates where the natural shape can be retained the needed supply of bearing wood can be kept up by merely cutting back the growth that reaches out beyond the line of symmetry and shortening some of the inside growth.
(2. Seed Variation of Cultivated Plants) Many of our best shrubs bear flowers on the points or top of new-growth that starts from wood of the preceding year's growth, like the grape and quince; others develop flowers on the preceding year's growth. With these classes it is evident that cutting back the top will remove the bearing wood, especially when cut below the new wood. Hence such shrubs are headed in as soon as the flowers fade. This light cutting back of points of growth starts an additional growth of new shoots to flower the next spring. Some well-known shrubs of this class are flowering almond, snowball, weigelia, exochorda, forsythia, Prunus triloba, lilac, tamarix, and some spiraeas.
(3. Commercial Seeds) A few well-known species, such as barberry, cara-gana, white fringe, bush honeysuckle, and kalmia, do not need pruning except when they get some age, when the pruning consists in cutting out some of the old wood, as in pruning the currant and gooseberry.
As a rule, in about all shrub pruning the operator must observe from actual inspection whether the flowers grow on the ends of terminal or lateral shoots of that season's growth, or on the ends or sides of the preceding year's growth.
The varieties and species with upright habit of growth and upright leader, such as the spruce and fir, should have a low, quite broad base and symmetric form of top. In transplanting on the lawn from the nursery the most perfectly developed side should be turned to the south. This side, which in nursery has had the most light and air, usually needs, when planting, some shortening of the points of growth. The after care will be in the way of pinching too vigorous points of growth as observed, and if the leader is broken off by sleet or stock, provide another upright point by turning up a side shoot and tying it to the stub. With a little continued care in merely pinching terminal buds the required form can soon be established. The species that do not form leaders, such as the hemlock, only need attention in the way of equalizing growth by pinching projecting points of extension, especially on the north side.