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Spring Bud Break

May 5, 2020

Contributed by Jon L. Peter, Curator & Plant Records Manager

As spring continues to unfold, it reveals a multitude of delight from early spring flowers, emerging perennials and woody plant buds breaking dormancy. This eruption of growth from the soil when looking at herbaceous plants and the eruption of growth from buds of woody plants is a great spectacle of spring. The interesting component is that this growth, for the majority of cases, is pre-determined during the previous growing season.

Each year, we see herbaceous perennials grow, flower, fruit and set seed through spring, summer and fall and then begin their dormancy, when the leaves and stems turn brown and lifeless. Important nutrients and water are pushed back into the root system to allow these plants to overwinter successfully. “Buds” are formed at the crown of the herbaceous plants by the time they go dormant and are waiting there, ready to burst forward when conditions are favourable again the following year. Just think of the “eyes” of Hosta.

In woody plants (trees, shrubs, sub-shrubs, and vines), growth is maintained above the soil from year to year. Sometimes the leaves and/or needles (in conifers) remain in tack through the winter and can even function (photosynthesize) when conditions are favourable during the winter season but are usually dormant through this season. In deciduous woody plants, the plants grow, flower, fruit and set seed through spring, summer and fall and then begin their dormancy by shutting down functions in the leaves, moving nutrients and water around the plant, and then abscission of the leaves results in a dormant plant. In most cases, the information for shoot, leaf and flower growth is determined the previous growing season. This growth information is contained within the buds of the woody plants.

Those buds can come in a variety of shapes, textures, colours, and designs in order to protect leaves, shoots and flowers through winter, so they are ready when conditions are favourable for growth again the next year. The characteristics of buds are good identification features and are generally more straight forward than identification by way of leaf characteristics, since growth and characteristics of leaves are variable and can be altered by current environmental conditions.

The buds of woody plants are generally located at the terminals of branches (called terminal buds), at the axil of the leaves (axillary buds or lateral buds) or sporadically on the plant (adventitious buds) found on roots, trunks, shoots and even on leaves. The buds are usually protected by scales (modified leaves) which assist in getting them through winter. There can be various types of buds on the same plant and even on the same branch. These are vegetative buds, reproductive buds, or mixed buds. Vegetative buds hold the information for producing leaves and shoots, reproductive buds hold the flower information and mixed buds have vegetative and reproductive information within. If you were to dissect a bud in mid-winter, you will see the leaves and flowers already formed within.

As spring temperatures rise, we begin to see changes in the buds. They will begin to swell, enlarge and elongate. In late winter/early spring we see flower buds opening like the early flowers of Silver Maple (Acer saccharinum) and Red Maple (Acer rubrum), whose flowers emerge from multi-scaled buds well before any vegetative buds emerge. We see spring ephemerals pushing new growth from the below ground bulbs, corms, and tubers. We also see leaves, stems and flowers of perennials thrusting through the soil. All this action and new growth can happen rapidly, but it is this stage of growth which can be beautiful, interesting, wonderful, sometimes strange, and always welcomed to observe in spring.

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