Hi Janet,

Because the other lavender beds on the same side of the house performed normally, I'd focus on something that changed specifically in that one bed rather than assuming it was weather-related.

Possible Causes of Sudden Poor Blooming in One Bed

For English lavender (Lavandula angustifolia), the most common causes of sparse, spindly flowering are:

1. Increased Soil Moisture or Poor Drainage
Lavender dislikes wet feet. Even within the same yard, one bed may collect more runoff, have heavier soil, or stay wetter longer.
Signs:
Fewer flower spikes
Thin, weak growth
Some stem dieback
Plants appear alive but lack vigor
If that bed received more irrigation, accumulated mulch against the crown, or experienced drainage changes, that alone could reduce flowering. Lavender generally flowers best in dry, well-drained soil.

2. Soil Became Too Rich
Lavender evolved in lean, rocky soils. If compost, manure, lawn fertilizer runoff, or nitrogen-rich fertilizer reached that bed, the plants may produce weak vegetative growth and fewer flowers. Excess nitrogen is a well-known cause of reduced bloom production.

3. Plants Becoming Woody
Lavender often blooms poorly when the center becomes woody and aging stems accumulate. Flower production shifts farther out on the stems and can become sparse if plants are not pruned regularly.
Look for:
Bare woody center
Green growth only at stem tips
Plant opening up in the middle

4. Winter Damage
In Michigan, one planting area may have a different snow cover pattern, exposure to wind, or freeze-thaw cycle. Partial winter injury often results in:
Delayed growth
A few weak shoots
Reduced flowering that season
Check for brown, brittle stems among otherwise green
growth.

5. Increased Shade
Even a relatively small change can matter:
Tree growth
Shrub growth
Neighboring plants becoming larger
Lavender generally requires at least 6-8 hours of direct sun to flower heavily.

6. Crown or Root Decline
If only those two plants declined, inspect the crown where stems emerge from the soil. Root rot or crown rot often begins with:
Reduced flowering
Weak shoots
Sections of the plant dying back

How and When to Prune English Lavender in Michigan
For Lavandula angustifolia, pruning is one of the most important maintenance practices.
Main Pruning: Early Spring
In Genesee County, I recommend:
Late March through April
Wait until new growth is visible
Remove winter-killed stems
Shape the plant into a rounded mound
Cut back approximately one-third of the green growth, but avoid cutting deeply into old leafless wood. Lavender frequently fails to regenerate from old bare wood.

After Blooming
After the main flush of flowers:
Remove spent flower stalks.
Lightly reshape the plant.
Many gardeners shear off the flower stems and about 1 inch of leafy growth underneath.
Regular annual pruning helps prevent the woody, sparse center that eventually reduces flowering.

For Older Overgrown Plants
If the plant is mostly woody with little green growth:
Do not cut it to the ground.
Reduce gradually over 2-3 seasons.
Always leave green foliage on stems.
Even English lavender is much less reliable at resprouting from completely bare wood.

Michigan-Specific Rule of Thumb
For southeast and mid-Michigan:
Spring: major shaping/pruning.
Mid-summer: remove spent blooms.
Fall: avoid heavy pruning because tender regrowth can be damaged by winter.

My first suspicion, given that the other beds were fine and the plants were good the previous year, would be either winter injury, localized drainage/moisture differences, or the plants beginning to get woody from inadequate annual pruning. Those are the three causes I see most often in mature Michigan lavender plantings.

Sources:

Landscaping76493.pdf

324611.pdf