previous
  • Rex Begonias
    Rex Begonias
  • Pick Plants for Fragrance
    Pick Plants for Fragrance
  • 10 Seed-Starting Tips
    10 Seed-Starting Tips
  • Garden Design Basics
    Garden Design Basics
  • Planting the Right Way
    Planting the Right Way
  • 3 Ways to Design with Containers
    3 Ways to Design with Containers
  • Rhodies to Treasure
    Rhodies to Treasure
  • DIY A-Frame Veggie Trellis
    DIY A-Frame Veggie Trellis
  • 10 Combinations for Shade
    10 Combinations for Shade
  • 20 Gardenworthy Self-Sowers
    20 Gardenworthy Self-Sowers
  • Black Plants Done Right
    Black Plants Done Right
  • Using Containers as Elements of a Design
    Using Containers as Elements of a Design
  • Seed Starting in Speedling Trays
    Seed Starting in Speedling Trays
  • How to Grow Mustard
    How to Grow Mustard
  • Bold and Beautiful Zinnias
    Bold and Beautiful Zinnias
  • Indoor Seed Starting Materials List
    Indoor Seed Starting Materials List
  • Get your FREE Everyday Roses download now!
    Get your FREE Everyday Roses download now!
  • Building Better Borders
    Building Better Borders
  • Plant Finder: Spring Plants
    Plant Finder: Spring Plants
  • NEW Video Series: There's a Better Way
    NEW Video Series: There's a Better Way
  • Pantone Color of the Year 2014: Radiant Orchid
    Pantone Color of the Year 2014: Radiant Orchid
  • Homegrown / Homemade
    Homegrown / Homemade
  • Go Green on the Patio
    Go Green on the Patio
next

The timing of leaf emergence

Q: Why do some plants leaf out in spring before others?

C. James McGrath, Bristol, RI

Emerging foliage can indicate when it's time to plant. Emerging foliage can indicate when it's time to plant. Photo/Illustration: Haley Aselin Graves

A: Tolly Beck, a horticulture educator for the Cornell Cooperative Extension and an instructor at the  New York Botanical Garden , replies: Hereditary genetics plays a major role in determining when a plant will begin to leaf out. Inherited genes are those that are passed along in plants from one generation to another. Certain genes dictate the conditions necessary for leaf buds to begin active growth in a particular plant. Each plant, therefore, has a predetermined set of conditions that signal it to leaf out.

One of the earliest trees to leaf out is the Ohio buckeye (Aesculus glabra, Zones 3–7). Leaf emergence in this plant occurs from late March to early April, with flowering occurring in mid-May. A short period of dormancy initiates its early leaf growth. Later leaf emergence is seen in the Eastern redbud (Cercis canadensis, Zones 4–9), where flowers are produced from March to April before the leaves begin to emerge. The Eastern redbud requires a longer period of warm days to initiate leaf growth. These are examples of inherited characteristics that will continue to be found in each generation of these particular trees.

The date at which plants commonly leaf out can be affected by the weather and other environmental factors. Spring temperatures, winter chilling, cloudy weather, the previous autumn’s conditions, and soil moisture all have an influence on when a plant will leaf out. Trees will often leaf out earlier when spring temperatures are warmer than usual.

The study of the relationship between certain biological events (like leaf emergence) and climatic conditions is a science called phen­ology. By observing specific phenological events over many years, certain reliable correlations can be made. One such correlation is that when leaves first appear on common lilacs (Syringa vulgaris and cvs., Zones 4–8), it is the correct planting time for beets, carrots, cole crops (belonging to the Cruciferae or mustard family), lettuce, and spinach. This correlation is made because the conditions that are necessary for the common lilac to produce its first leaves are the same conditions necessary for optimal initial growth for these specific crops.

With the progression of genetic adaptations and changing climatic conditions, there will likely be some interesting developments in the timing of leaf emergence. If a warming trend consistently leads to earlier leafing out, there may be a shift northward for many plants. While this sounds like a wonderful situation for gardeners, it may create problems for pollinators and bird species that may not be able to adapt at the same rate.

From Fine Gardening 103, pp. 72