Heaven forbid I should ever figure this out.
The gardener expects some confusion, and particularly in early spring. My observation in this garden, for whatever little good that might be, is that ‘Dr. Merrill’ magnolia (Magnolia × loebneri ‘Merrill’, below) flowers a day or two before ‘Royal Star’ (Magnolia stellata ‘Royal Star’) which is also when the purple flowered saucer magnolias (Magnolia soulangeana) bloom in sunnier gardens in the neighborhood. Almost certainly, the earlier flowering is because ‘Dr. Merrill’ stands further up the slope and is a bit less shaded by the towering maples and tulip poplars that border the garden.
In winters when February is mild, flowering of both might be a week before the start of March, but most years the magnolias (‘Royal Star’,below) flower in early March. If late winter temperatures are consistently cold, flowering might be delayed for several weeks, as was the case the past two years when flowers overlapped with redbuds into early April .
Flowers of the early magnolias are regularly damaged by frost over their ten days in bloom, which is occasionally a disappointment, but most years there are four or five days when flowers are perfect so that the gardener holds no grudge against the cold. For the more cautious gardener who requires flowers that are less prone to frost damage, the wise option is to plant the splendid purple flowered ‘Jane’ (Magnolia ‘Jane’, below), which flowers two weeks later.
Except this year, and this is where confusion sets in as all magnolias are flowering at once, though ‘Jane’ is just beginning as the others are at their peak. To the less experienced gardener there would seem no advantage in planting a magnolia that flowers only three days later, and of course all will be threatened as temperatures plunge over the weekend. I will, of course, hope that the frost is not so cold, and that flowers escape serious damage, but there is always next year, and perhaps then the early will flower earlier, and the late flowers will follow frost.