Whether a plan has been prepared or not the question must ultimately be when to plant. This is a most important decision and must not he taken lightly as the ultimate success of the dahlias may depend upon the rightness of the answer.
There is one thing that cannot be overstressed, the dahlia should be planted as soon as soil and weather conditions permit. And this often means that the calendar has to be very largely ignored and the weather reports studied instead, together with an intelligent anticipation of local conditions. Where plants are concerned it is useless planting when the soil is cold and the weather is cold or there arc icy winds expected.
If this plan is adopted it is best to plant in groups of three to six dahlias, again carefully chosen as to height, putting a block of taller varieties at the back of the border, with dwarfer perennials – not too dwarf of course – in front ; or a group of varieties of medium height, in front of tall perennials such as the rudbeckias and so on. The variations on this theme are unlimited.
The condition of the soil is a wonderful guide. If at the usual planting time it is fairly warm, just nicely moist and really workable, by all means go ahead with planting, particularly if the weather conditions are also reasonable. Obviously the type of soil and the situation will have some bearing on the matter, for a heavy cold soil will take much longer to warm up than a light well drained soil, and a sheltered site will warm up even more quickly.
The main point to be emphasised is that if planting be done in a cold soil, or during a spell of cold winds and rain, the plants will remain static, neither making fresh root nor top growth, and may even deteriorate. Well this is just what happens when plants are put out in bad conditions. They receive a check to their growth, almost as a human being takes a chill, and it takes them some while to recover from this check.
One of the major troubles will be insect damage, as the pests will tend to migrate from the less herbaceous stuff to the rich fare offered by the succulent dahlias. Dusting or spraying with good insecticides will minimise this undesirable factor.