While it’s nearing the end of the line this time of year for most of the landscape, there’s one group of plants when it’s prime time to start them – spring-flowering bulbs.
Led by tulips, daffodils, and hyacinths, these spring bloomers are best planted in October and even into early November.
But why do they need to go into the ground now when spring is when most everything else is planted?
The reason relates to the underground, bulbous origin of these plants and the life cycle around it.
Spring-flowering bulbs such as tulips, daffodils, hyacinths, crocuses, and lesser known species such as snowdrops, winter aconite, Siberian squill, glory-of-the-snow, and most alliums are all actually embryos that have tiny living plants inside.
When planted into the cooling soil of fall, the first thing these dormant bulbs (or closely related corms) do is send down roots. The roots develop while the bulb hormonally monitors the length of chilling time the rest of all and into winter.
Think of it as a sort of “biological clock.”
When the prescribed time has passed for each species, the bulb sends up above-ground shoots – usually leaf shoots first and then the stalks that produce flowers at the tips.
Different species have different chill-time and day-length requirements, which explains why, say, snowdrops can bloom as early as late January into February while most tulips don’t bloom until April or May.
That also explains why spring-flowering bulbs don’t do well in southern climates … they don’t get adequate cooling time over winter. Southern gardeners generally have to buy their bulbs “pre-chilled” (or cool them in refrigerators before planting) in order to get decent blooms.
Once spring bulbs bloom, almost all of them die back naturally and stay dormant underground throughout summer.
As soil temperatures cool, existing bulbs send down new roots to start a new cycle. This is the timing that gardeners are tapping into when they add new bulbs to the landscape.
Most spring bulbs are perennial ones, meaning they come back year after year and often expand their colonies by producing attached bulblets.
Daffodils, Siberian squill, camassia, and glory-of-the-snow are particularly good at perennializing, while hyacinths, fritillaria, and many tulips tend to fizzle out after a good year or two.
To encourage return, the best thing a gardener can do is allow the bulb foliage to stand each spring at least until it yellows – or better yet, until it browns and dies back.
Green foliage takes in sunlight to manufacture sugars that are stored in the bulbs to “recharge” them for future bloom (the photosynthesis that your biology teacher talked about in high school).
A scattering of balanced, granular fertilizer each spring and/or fall also can help, as can digging, dividing, and replanting bulb clusters when colonies are getting too thick.
Replanting into sunnier areas also can help when expanding trees begin shading bulb colonies that aren’t blooming as well as they once did.
The two best times to divide bulbs are right after the foliage dies back in spring (it’s easier to tell then where to dig) and the same time when it’s ideal to plant new bulbs – October to early November.
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