This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
Greenhouse plants generally require more care during this month than at any other period, watering only when necessary; and to give enough requires practice how to ascertain this. With many plants the mischief from bad watering is only seen after the season is advanced. Chrysanthemums, when done flowering, are the better of protection in a frame or pit, especially when early cuttings are wanted. They may be put in a frame this month, and kept plunged and close till signs of flagging are past; then they should have plenty of air. Flowering shrubs, bulbs, and other plants to make the show-house gay, may be placed into heat (say 50° to 55°) every two or three weeks, to meet the demand. Cinerarias, Calceolarias, and Primulas should be kept near the glass till they come into flower. Those Cinerarias which are flowering and have their pots full of roots, may have manure-water. Camellias, Epacris, and Heaths now flowering may have more water than those not flowering. Drainage and clean surfaces are very important to such plants. Change the atmosphere by applying a little fire-heat to expel damp. In severe weather it is injurious to keep high temperature by fire-heat; 40° to 45° is safe. Keep foliage-plants free from dust, and insects must have no footing on them.
Climbers may be kept within bounds : except those which are flowering, the most of them will be about starting into growth.
Abundance of plants are now in bloom, both hard and soft wooded. Hardy plants which have been forced are now very gay, and of great service where cut-flowers are in request. Successions, to keep a continuous supply till they are plentiful out of doors, must be put into warmth periodically. An ordinary frame or pit, shut up with moisture and sun-heat, will bring many useful things on rapidly. Rhododendrons, such as the nobleanum class, will turn in without such aid : outside they are in flower, but frost cuts them down very frequently. Deutzias, Spiraeas, White Lilacs, Mock Oranges, White Thorns, Double Cherries (single ones are good, and may also bear fruit), along with Roses of great variety, will go far to make up a good collection of white flowers. Azaleas and Camellias are most useful as show plants at this season. Azalea Borsig, of the semi-double whites, is of much value, and flowers readily with little heat. Camellias and Azaleas which are to flower in autumn should be encouraged to finish their growth and set their buds as early as possible. Healthy root-action is of great moment in the formation of flowers and their development. Oranges and all hard-wooded plants should have a general overhaul after they have flowered and are breaking into fresh growth.
Some require cutting back, and, after they break into fresh growth, have their balls of soil reduced, and repotted into same size of pots. Good drainage and healthy soil made rather firm are indispensable for hardwood plants. Nothing which is expected to grow into good specimens should starve for want of root-room. Cinerarias and Calceolarias to flower late may be shifted into larger pots, or be allowed to root through into soil placed in larger pots on which the plants are set. Pot on a quantity of plants for summer flowering : Pelargoniums, Fuchsias, Double Petunias, Kalosanthes, and suchlike, make a show. The last does not do with much pot-room. Air freely, but exclude frosty winds. A sprinkling of water may be necessary over the plants and on the floors during hot drying weather : 50° to 55° is warm enough without sun. Climbers may be moderately pruned, and not too stifly trained.