Vegetable Crop Planting and Phenology

Lilac in full bloom

Lilac in full bloom

Events in the natural calendar can be used to guide planting times in the vegetable garden. The study and observation of seasonal events and their correlation to plant, insect, and animal life is called phenology.

Modern phenology got its start in England with the observations of naturalist Robert Marsham. Marsham began recording the connections between natural and seasonal events in 1736 and kept at it for more than 60 years. Many American universities have ongoing phenology studies underway today.

But phenology has ancient origins; one Chinese proverb says: “Spring is sooner recognized by plants than by men.”

The lifecycle of the common lilac is an often used guide in phenology studies and garden planning and planting. The leafing out and progression of lilac blooms—from bud to flower fade—can aid the vegetable gardener from year to year. For example, after years of observing the lilac, naturalists have concluded that it is safe to plant tender bean, cucumber, and squash seeds when the lilac is in full bloom.

Phenology generally looks at climate, weather, and temperature triggers and how they correlate to events in the plant, animal, and insect worlds.

Other notable phonological events: When the saucer magnolia blooms early spring has arrived; when wild chicory blooms summer has arrived.

Vegetable Planting, Signs in Nature, and Phenology Guide:

  • Beans: Plant beans when lilac is in full bloom, also cucumber seeds and squash seeds.
  • Beets: Plant beets when lilac is in first leaf and dandelions are in bloom, also carrots, cabbage family crops, lettuce, and spinach.
  • Broccoli: Plant broccoli when lilacs first begin to leaf out and dandelions are in bloom.
  • Brussels sprouts: Plant Brussels sprouts when lilacs first begin to leaf out and dandelions are in bloom.
  • Cabbage: Plant cabbage and cabbage family crops (broccoli, Brussels sprouts, collards) when lilacs first begin to leaf out and dandelions are in bloom, also beets, carrots, lettuce, and spinach.
  • Cabbage for spring: Plant spring cabbage in fall when mock orange is in full bloom
  • Carrots: Plant carrots when lilac is in first leaf and dandelions are in bloom, also beets, cabbage family crops, lettuce and spinach.
  • Collards: Plant collards when lilacs first begin to leaf out and dandelions are in bloom.
  • Corn: Plant corn when apple blossoms begin to fall and when oak leaves are the size of a squirrel’s ear.
  • Cucumber: Plant cucumber seeds when lilac is in full bloom and when the blooms just start to fade, also bean seeds and squash seeds.
  • Eggplant: Transplant eggplant irises bloom and daylilies start to bloom, also melons and peppers.
  • Hardy, cool-season spring crops: plant hardy crops when plum and peach trees are in full bloom.
  • Lettuce: Plant carrots when lilac is in first leaf and dandelions are in bloom, also beets, carrots, cabbage family crops, and spinach.
  • Melons: Transplant melons when irises bloom and daylilies start to bloom, also eggplant and peppers.
  • Peas: Plant peas when daffodils and forsythia are in full bloom.
  • Peppers: Transplant peppers when irises bloom and daylilies start to bloom, also eggplant and melons.
  • Potatoes: Plant potatoes when the first dandelions bloom.
  • Spinach: Plant spinach when lilac is in first leaf and dandelions are in bloom, also beets, cabbage family crops, carrots, and lettuce.
  • Squash: Plant squash seeds when lilac is in full bloom and just as the blooms fade, also bean seeds and cucumber seeds.
  • Tender, warm-season summer crops: Plant tender crops when you see new growth on grapes
  • Tomatoes: Plant tomatoes when daylilies start to bloom or lily-of-the-valley plants are in full bloom or flowering dogwood are in bloom.

Vegetable Garden Pests Phenology:

  • Apple maggot moths are at their peak when Canada thistle blooms; protect apple fruits.
  • Mexican bean beetle larvae appear when foxglove flowers open.
  • Cabbage root maggots are active when wild rocket blooms.
  • Japanese beetles arrive when morning glory vines begin to climb.
  • Squash vine borers are at their peak when chicory blooms; protect pumpkin plants.
  • Tent caterpillars are hatching when crabapple trees are in bud; begin caterpillar controls.

Note on the Bloom of Lilacs:

Lilacs bloom first in the west and south and then in the east and north. Naturalists have observed that most phenological events on a large scale progress from west to east and south to north. This progression is known as ‘Hopkin’s Rule” (named for U.S. Department of Agriculture entomologist Andrew Hopkins) which states that phenological events are delayed by four days per degree of north latitude and 1¼ days per degree of east longitude. But there are exceptions; in particular, altitude and topography will impact the progression of natural events.