This section is from the book "A Dictionary Of Modern Gardening", by George William Johnson, David Landreth. Also available from Amazon: The Winter Harvest Handbook: Year Round Vegetable Production Using Deep Organic Techniques and Unheated Greenhouses.
"The Dahlia may be advantageously forced by potting the roots in February, and letting them remain in frames till June; when they will begin to flower, and may be turned out into the open border." - Gard. Mag.
"To grow Dahlias in.pots," says Dr. Lindley, "you must select the dwarfer and more freely flowering kinds, the taller ones being totally unsuited for that purpose. After they are started, and when the shoots are about three or four inches long, pot them singly into small sixties in any light rich soil; water them freely, and place them in a hot-bed, keeping them close for a day or two, and shading them during sunshine. They will, if properly attended to, be rooted in about ten days, and should then be removed to a much cooler place, and have plenty of air. When established, shift them into larger pots, and finally, before placing them out of doors, repot them, either into twelves or eights, according to the size of your plants.
"Top the leading shoots to make them bushy; and when the danger of frost is over, they may be plunged in the open border, which saves much labour in watering; but even then they must be watered copiously in dry weather. They will flower freely all the summer and autumn, although the blooms will not be so fine upon plants grown in pots as upon those in the open border. After flowering, cut the tops oft', and place the pots containing the roots in a dry cellar, or other place, where they will be secure from frost during the winter. Young plants struck from cuttings flower much better in pots than the old roots." - Gard. Chron.
Dr. Lindley says, "The dimensions of a Dahlia stand for twelve blooms should be twenty-two inches long by sixteen and a half wide, four in depth, and five and a quarter from tube to tube: sixteen and a half by eleven and a quarter will be the proportion for a stand of six. The surface of stands is generally painted a light green; a colour which shows the flowers off to the greatest advantage." - Gard. Chron.
 
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