Pruning Hydrangeas in Southeast Michigan: The Ultimate Guide to Old Wood and New Wood Varieties

Hydrangeas are one of the most beloved shrubs in gardens throughout southeast Michigan, prized for their large, vibrant blooms that light up landscapes from spring through fall. But, like any garden plant, hydrangeas require the proper care to thrive and bloom to their fullest potential. One key aspect of hydrangea care is pruning, but the right time to prune and the technique used depends on the type of hydrangea you have. In this post, we’ll walk you through the proper times to prune different types of hydrangeas, including the differences between old wood and new wood, and provide helpful pruning tips for each.

Understanding Old Wood vs. New Wood Hydrangeas

Before diving into the specifics of pruning, it’s important to understand the difference between old wood and new wood hydrangeas.

• Old Wood Hydrangeas: These hydrangeas bloom on stems that were formed the previous year. This means the buds for next year’s flowers have already set during the current growing season, and they will bloom in the spring or summer on the older wood. Common examples of old wood hydrangeas include Hydrangea macrophylla (Bigleaf Hydrangea), Hydrangea quercifolia (Oakleaf Hydrangea), and Hydrangea anomala (Climbing Hydrangea).
• New Wood Hydrangeas: These hydrangeas bloom on stems that grow in the current season. This means they form buds and flower on the fresh growth from the current year. Common examples of new wood hydrangeas are Hydrangea paniculata (Panicle Hydrangea) and Hydrangea arborescens (Smooth Hydrangea, such as the popular ‘Annabelle’ variety).

Knowing whether you have an old wood or new wood variety is essential for pruning at the correct time and ensuring healthy blooms for the following season.

Pruning Old Wood Hydrangeas

For old wood hydrangeas, such as Hydrangea macrophylla and Hydrangea quercifolia, the key to pruning is timing. These hydrangeas produce buds in late summer or fall on the previous year’s growth, so pruning too early can remove these buds, potentially resulting in fewer or no flowers the next season.

When to Prune:

• Best Time: Late winter to early spring (late March to early April in southeast Michigan).
• Why Then? Pruning these types of hydrangeas during late winter or early spring ensures that the buds formed in the previous season are left intact while still removing any dead or damaged wood. Waiting until late winter or early spring also helps to avoid pruning during a late frost, which can damage the plant if it’s pruned too early.

How to Prune:

1. Remove Dead Wood: Start by cutting out any dead, damaged, or diseased stems. These can be identified by their brown or gray color, compared to the healthy green or reddish-brown of living wood.
2. Shape the Plant: Old wood hydrangeas generally don’t require heavy pruning. Trim back about 1/3 of the older stems to the ground or to a healthy bud to help maintain a compact shape. Be careful not to over-prune, as this can reduce the number of flowering stems.
3. Thin Out the Center: If your hydrangea is particularly dense, thin out some of the older branches to allow more sunlight and air to reach the center. This helps improve airflow and reduces the risk of disease.

Note: If your hydrangea has been allowed to grow too large or has become leggy, you can prune back more aggressively, but this may reduce flowering for the next season as it will take time for the plant to regrow. Keep in mind that any drastic pruning should be done with caution and only when absolutely necessary.

Pruning New Wood Hydrangeas

New wood hydrangeas, like Hydrangea paniculata and Hydrangea arborescens, are much more forgiving when it comes to pruning. These varieties produce flowers on new growth, meaning you don’t have to worry about cutting off buds for next year’s blooms.

When to Prune:

• Best Time: Late winter to early spring (late March to early April in southeast Michigan), or even after they have started to leaf out in early spring.
• Why Then? Since these hydrangeas bloom on new wood, you can prune them in late winter or early spring without worrying about cutting off buds. Pruning during this time ensures the plant has time to put out new growth and form flowers.

How to Prune:

1. Remove Dead or Damaged Stems: Start by cutting out any damaged or diseased wood to promote healthy new growth.
2. Shape the Plant: New wood hydrangeas can be pruned more aggressively than old wood varieties. You can cut them back to about 6-12 inches above the ground for a more compact shape or to promote stronger growth. If you prefer a larger shrub, you can prune less aggressively.
3. Thin the Plant: If your hydrangea is dense, thin the interior branches to allow more air circulation and sunlight penetration, which helps prevent disease and promotes better flower production.

Note: New wood hydrangeas benefit from more frequent and more aggressive pruning than their old wood counterparts, which makes them perfect for gardeners who prefer to maintain a low-maintenance, compact shrub. Cutting them back in late winter or early spring encourages them to sprout vigorously and bloom profusely in the summer.

Special Considerations for Southeast Michigan

The climate in southeast Michigan can be unpredictable, with late frosts sometimes occurring even in April. These late frosts can damage tender new growth, which is why it's essential to keep an eye on weather forecasts before you prune your hydrangeas.

• Late Frosts: If a late frost is predicted after you’ve pruned your hydrangeas, consider covering them with frost cloths or burlap to protect the new growth. For old wood hydrangeas, this won’t affect the buds that have already set, but new wood hydrangeas could suffer frost damage to their tender shoots.
• Winter Damage: In southeast Michigan, hydrangeas can sometimes suffer from winter burn, especially if they’re exposed to harsh winds or extreme cold. If this happens, prune out any brown, dried, or damaged wood in early spring to promote healthier growth.
• Microclimates: Consider the microclimate of your garden when deciding the best time to prune. If your hydrangeas are in a sheltered area, they may warm up earlier in the season, while those in more exposed locations may still be subject to late frost.

Common Pruning Mistakes to Avoid

1. Pruning Too Early: As mentioned, pruning too early can damage flower buds, especially on old wood hydrangeas. Always wait until late winter or early spring before pruning.
2. Over-pruning: Cutting too much of the plant can reduce flowering, especially with old wood hydrangeas. Prune only what’s necessary for shape and health.
3. Not Pruning Deadwood: Removing dead or diseased stems helps prevent pest and disease problems while encouraging healthy new growth. Don’t skip this step, as it’s essential for the health of your hydrangea.

Conclusion

Proper pruning is crucial to maintaining healthy, vibrant hydrangeas, and understanding whether you have an old wood or new wood variety will help you time your pruning for maximum bloom potential. In southeast Michigan, late winter to early spring is the ideal time to prune most hydrangeas, with some flexibility depending on your specific variety and the weather conditions. By following the right techniques for each type, you’ll ensure your hydrangeas remain beautiful year after year, adding color and charm to your garden throughout the seasons.

Happy gardening!