Penny Mac is a bigleaf hydrangea cultivar known for large clumps of flowers and a long summer bloom season, with new buds forming continuously all season. The pink blooms can shift to blue when the soil turns more acidic, which makes the shrub a favorite for gardeners who like to experiment with color. The plant is long-lived, comfortable in partial shade and moist soils, and named in honor of Penny McHenry, founder of the American Hydrangea Society, who received the original plant as a gift in 1975 and shared it with fellow enthusiasts. The shrub shares the genus with other garden favorites, including oakleaf types whose oakleaf hydrangea care routines favor different pruning and sun tolerance. With mature dimensions of 4 to 6 feet tall and 3 to 4 feet wide and hardiness across zones 5 through 9, Penny Mac fits a wide range of garden beds.
Penny Mac Hydrangea Care Basics
The reputation of Penny Mac rests on reliability. Where many bigleaf hydrangeas bloom only on old wood and skip flowering after a hard winter, Penny Mac sets buds on both old and new growth, so it usually blooms even when spring frosts kill the previous year’s stems. That remontant habit produces the long June-to-September season that makes the shrub so popular.
Why Penny Mac Blooms When Other Bigleafs Do Not
Most Hydrangea macrophylla varieties form next season’s flower buds in late summer on stems that grew that year. If those stems die over winter, the shrub leafs out but stays flowerless. Penny Mac avoids that failure by also pushing buds on fresh growth each spring, which is why it recovers from cold damage better than older cultivars.
Site and Spacing
Give each plant room to reach its mature spread of 3 to 4 feet without crowding the next shrub. Morning sun with afternoon shade suits it best in most regions, and a spot protected from strong wind keeps the large leaves from tattering. If your garden gets full sun for most of the day, panicle hydrangea care for Limelight shrubs is a more forgiving match for that exposure.
Light, Soil, and Water Requirements
The fundamentals of hydrangea care apply to Penny Mac: consistent moisture, rich soil, and protection from harsh afternoon sun. Get these basics right and the shrub needs little else.
Sun Exposure: Morning Sun, Afternoon Shade
Penny Mac wants partial sun, which usually means four to six hours of morning light and shade by early afternoon. In zones 5 and 6, more sun is tolerable; in zones 8 and 9, too much afternoon heat wilts the leaves and shortens bloom life. Deep shade produces fewer flowers and weak, stretched stems.
Soil Type and Drainage
Rich, loamy, well-drained soil gives the best root growth. Amend heavy clay with compost before planting, and consider a raised bed where water pools. The roots are shallow and wide, so protect the area around the base from foot traffic and digging.
Watering and Mulch
Established shrubs need about 1 to 1.5 inches of water per week, more during heat waves. A soaker hose or drip line delivers moisture without wetting the leaves, which reduces foliar disease. Mulch 2 to 3 inches deep with shredded bark or leaves keeps the root zone cool and slows evaporation.
| Attribute | Requirement |
|---|---|
| Mature size | 4 to 6 feet tall, 3 to 4 feet wide |
| Sun exposure | Partial sun, morning sun with afternoon shade |
| Soil | Rich, loamy, well-drained |
| Soil pH | Acidic soil gives blue flowers, alkaline gives pink |
| Bloom time | June to September |
| Hardiness zones | 5 through 9 |
| Water needs | 1 to 1.5 inches per week |
Pruning Penny Mac Hydrangeas
Because Penny Mac blooms on old and new wood, pruning mistakes rarely cost the whole season, but good timing still produces more flowers. The two windows that matter are late winter, for removing dead wood, and midsummer, for light shaping after the first flush.
When to Prune
Wait until early spring, when new growth begins, to identify which stems died over winter; dead stems stay bare and brittle while live ones push buds. Avoid pruning in fall, which removes next year’s flower buds and encourages tender new growth before frost. Late-winter cuts on old wood reduce early blooms, so limit them to dead and damaged stems.
How Much to Cut
- In early spring, cut dead stems to the base once live buds show below the damaged section.
- Remove crossing, rubbing, or weak branches to open the center.
- After the first bloom flush, deadhead spent flowers just above a healthy leaf pair.
- Every three to four years, remove the oldest third of the stems at ground level to renew the shrub.
- Leave the structure alone in fall and let old stems protect the flower buds.
Smooth hydrangeas tolerate hard annual cuts, but bigleaf types like Penny Mac do not need them; heavy shearing removes wood that carries buds. If you grow other types, note how Annabelle hydrangea care differs, since smooth hydrangeas can be cut to the ground and still bloom the same summer.
Changing Flower Color with Soil pH
Flower color in bigleaf hydrangeas tracks soil chemistry rather than genetics. The blooms contain pigments that turn blue when the plant can take up aluminum from the soil, and aluminum becomes soluble only in acidic conditions. Raise the pH and the same shrub produces pink flowers.
Pink to Blue: The Aluminum Connection
Soil pH below 6.0 keeps aluminum available and yields blue flowers, pH between 6.0 and 7.0 gives purple or mixed tones, and pH above 7.0 locks up aluminum and yields pink. To push toward blue, acidify with aluminum sulfate or elemental sulfur; to push toward pink, raise pH with dolomitic lime. White varieties do not respond because they lack the pigment.
Testing and Adjusting Soil pH
Test the soil before adding anything, since the current pH determines which amendment and how much. Garden-center test kits give a useful reading, and a lab test adds detail on aluminum and organic matter. Adjust gradually over a season and retest yearly, because pH drifts back toward the native soil. Container-grown plants are easier to control, since you replace the mix rather than fight the surrounding soil.
| Soil pH | Flower Color | Common Amendment |
|---|---|---|
| Below 6.0 | Blue | Aluminum sulfate or sulfur |
| 6.0 to 7.0 | Purple or mixed | Compost, maintain current pH |
| Above 7.0 | Pink | Dolomitic lime |
The full process of changing hydrangea color through soil pH adjustment takes patience, since the plant must take up the new chemistry through its roots before the next bloom cycle.
Propagating and Overwintering Penny Mac
Growing New Plants from Stem Cuttings
- Take 5 to 6 inch softwood cuttings in early summer from stems without flowers.
- Strip the lower leaves, leaving two or three at the top.
- Dip the cut ends in rooting hormone and insert them into moist perlite and potting mix.
- Cover the pot with a clear bag or dome to hold humidity, keeping it out of direct sun.
- Water to keep the mix evenly moist, and expect roots in four to six weeks.
- Pot rooted cuttings individually and harden them off before planting out.
Mature plants can also be divided in early spring before growth surges. The reliable bloom habit of bigleaf hydrangeas grown for summer blooms makes every successful cutting a future flowering shrub.
Winter Protection in Zones 5 and 6
Flower buds on old wood are the most cold-sensitive part of the plant. After the ground freezes, mound 6 to 12 inches of mulch, leaves, or pine needles over the crown, and wrap the stems with burlap or a wire cage filled with leaves. Container plants winter best in an unheated garage or against a sheltered wall, watered sparingly.
Pests, Diseases, and Bloom Troubleshooting
Common Pests and Diseases
- Aphids cluster on new growth and buds; knock them off with water or use insecticidal soap.
- Spider mites appear in hot, dry weather; raise humidity and rinse the foliage.
- Powdery mildew coats leaves when airflow is poor; thin crowded stems and water at the base.
- Botrytis gray mold attacks blooms in wet weather; remove affected flowers promptly.
- Deer and rabbits browse buds and young stems; use fencing or repellents where browsing is heavy.
Why Penny Mac Sometimes Fails to Bloom
- Late frost killed old-wood buds; new-wood buds usually still flower, so wait before judging.
- Too much shade limits bud set; move the shrub or thin overhead branches.
- High-nitrogen fertilizer pushes leaves at the expense of flowers.
- Fall pruning removed the buds already set for next year.
A hydrangea that skips a season is usually reacting to one of these four conditions rather than a disease. Correct the cause and the next cycle returns. For a longer show, pair Penny Mac with other repeat bloomers such as bicolor panicle hydrangeas, which flower on new wood and carry the garden into late summer.