Penny Mac is a bigleaf (mop-head) hydrangea that reblooms on both old and new wood, and that one trait decides whether it flowers where you live. A correction to the title’s vocabulary: this is a flowering shrub, so there is no days-to-maturity count from transplant, and nothing on it ripens in a single flush. What you can measure is winter cold, spring frost and soil pH. This page crosses those with what the North Carolina Extension source documents.
What Penny Mac actually is
The catalogue figure a tomato page would lead with does not exist here. The North Carolina Extension Gardener Plant Toolbox, the source behind this page, gives no days to maturity for Penny Mac, from transplant or from sowing. Anything quoted in that form belongs to a vegetable. What the source does give is three facts: the type, the hardiness range for that type, and the wood the flowers grow on.
The type is bigleaf hydrangea (H. macrophylla), listed for USDA zones 6a through 11b. That range belongs to this type and this cultivar. It is not a verdict for Hydrangeas in general, since the genus as a whole runs from 3a to 9b and varies enormously by type.
The mechanism matters more than the number. Bigleaf Hydrangeas form their flower buds the previous summer, so a late frost or a spring prune can remove the blooms before they open. Penny Mac’s source description adds the twist: it reblooms on old wood and on new wood. That explains why some bigleafs flower after a hard cut and others sulk for a year. It does not mean the old-wood buds are optional, only that there is a second chance behind them.
On size, the source gives the bigleaf type at 3 to 6 feet tall and wide, with a rapid growth rate and shallow roots. Penny Mac’s own dimensions are not documented in the source, so plan for the type’s spread. For how the other types compare, see Hydrangea Varieties.
What Penny Mac is good for
Not for the kitchen
Nobody should cook with this one. Among hydrangeas, only H. macrophylla is documented as toxic, and only when large quantities are eaten. The symptoms are nausea, stomach pain, vomiting and sweating. The toxic principle is a group of cyanogenic glycosides called hydracyanosides, found in the bark, flowers, leaves and stems. The source also flags cats, dogs and horses. It is a garden shrub, not a hazard, but it belongs where a grazing animal cannot make a meal of it.
Blue, pink or purple: what moves the color
The real use of a mop-head is its color, and Penny Mac’s changes with soil chemistry. Flowers turn blue when the soil pH is below about 5.5, pink above about 6.5, and purple in between. The mechanism is aluminum. Blue flowers need available aluminum in the soil, and acidity is what releases it. Aluminum sulfate acidifies the soil, and lime makes it more alkaline.
Feeding can undo the work. High-phosphorus fertilizer locks aluminum up in the soil, which pushes blue flowers toward pink. A gardener who switches to a bloom-booster and then wonders where the blue went has a feeding problem that shows up as a color problem.
Coffee grounds and citrus peel are the popular shortcut. The source repeats the belief that they can acidify soil enough to turn flowers blue, but the pH shift from coffee grounds is very small, and a kitchen scrap does not reliably deliver the aluminum the plant needs.
One limit applies here. Color-by-pH is true for bigleaf and mountain hydrangeas only. Panicle, smooth, oakleaf and climbing types go white, cream, pink or green as the season ages, whatever the soil.
Where it ripens in time, and where it is a gamble
For a shrub grown for flowers, “in time” means two things. Last summer’s buds have to survive winter and spring frost to open on old wood. And if they do not, the new growth has to have enough season left to flower on new wood before autumn frost. That is the arithmetic, in words: take your first fall frost, count back to the date your shrub leafs out, and see how many weeks of growth sit between them. The longer that stretch, the more useful the rebloom is as insurance. Separately, ask whether your winter lows and late spring frosts are likely to reach buds that formed the previous summer.
This page holds no frost-date table and no weather-station figures, so it names no reference cities. It would be wrong to invent them. Local frost windows, and the pruning timing that goes with them, belong on the per-state pages, and the answer depends on your zone and your hydrangea type.
What the source does let us compare is hardiness and bloom wood across types:
| Type | USDA zones | Flowers on |
|---|---|---|
| Bigleaf (Penny Mac) | 6a-11b | Last year’s wood; Penny Mac also reblooms on new wood |
| Panicle | 3a-8b | Current season’s growth |
| Smooth (e.g. Annabelle) | Zones not given here; the hardiest of the genus | New wood |
Read the table as a map of risk, not a set of bans. In zones 3 through 5, you sit below the range listed for Penny Mac’s type, and the source does not document how it fares there with protection. The source itself calls the panicle “a good substitute for the mop-head hydrangea in areas where that species is not winter hardy.” A gardener at that edge might look at a smooth type instead, such as Annabelle Hydrangea: When to Plant the Tomatoes That Ripen All at Once.
The two ways a season goes wrong
A frost table cannot show the failures that matter most on a hydrangea. The temperature limits that govern fruit set on a garden vegetable, cool nights that stop it and heat that sterilizes pollen, are tied to fruit. The source gives no comparable thresholds for a bloom-grown shrub, and this page will not borrow them.
The first failure is losing the buds. They formed last summer, so anything that removes or kills that wood removes the first flush: a late frost after buds have swollen, or a spring prune that treats the shrub like a plant that blooms on new growth. A frost calendar shows the first cause but not the second, and the second is the more common mistake.
The second failure is color drift. The season is not lost, but the flowers come out pink when you wanted blue. A pH creeping above about 6.5, or a switch to high-phosphorus fertilizer, will do it. Again, this only concerns bigleaf and mountain types.
Which matters more for Penny Mac? The reblooming habit softens the first failure, since new wood can still flower if the old-wood buds are gone. That makes bud loss a setback rather than a wipeout, though the rebloom depends on having enough growing season left. The color problem has no such backstop, and it is entirely in the gardener’s hands. For a comparison with another variety’s bloom habit, see Twist-n-Shout Hydrangea: When to Plant the Tomatoes That Ripen All at Once.
What it resists, and what it does not
The source grades no disease resistance for Penny Mac. There is no high rating and no intermediate rating, so treat the plant as unprotected. For the genus, the source names leaf spot, bacterial wilt and powdery mildew. Rust and bud blight are listed for panicle hydrangeas specifically, not for bigleaf, so they are not named here as Penny Mac risks.
The pest picture is mild. The source lists aphids, scales, nematodes and mites as “rarely a problem.” Deer are the exception. The source lists deer both as a damage agent and, on the genus page, under resistance to challenges, and the two entries disagree. What is observed is that hydrangeas get browsed. Do not count on deer resistance, and remember the buds sitting on last year’s wood are exactly what a browsing deer removes.
Growing it without the usual mistakes
Penny Mac’s rebloom habit changes the work. Think of it as a plant with two flushes rather than one: the old-wood buds you protect, and the new growth that covers you if they fail. The mistake this invites is assuming a spring prune is safe because the shrub reblooms. It can be survivable, but you give up the first flush. Prune right after flowering, and take the exact timing from your state page rather than from a national rule.
Site it for the type. The source recommends dappled sun, partial or deep shade, with protection from afternoon sun. Leave room for 3 to 6 feet of spread. Bigleafs are shallow-rooted, so a mulch layer helps. Soil can be clay, loam or sand, with good drainage; occasionally wet is acceptable. Maintenance is rated low, and growth is rapid for the type.
One habit worth adopting: when you cut dead, hollow stems, the source suggests trimming them to 12 to 24 inches and leaving them standing, because native bees nest in them. That applies to dead stems only, not to the live old wood that carries next year’s buds. If you want more plants, the source lists stem cuttings or layering as the propagation routes.
Common questions
How many days from planting until Penny Mac blooms?
The source publishes no such figure. Bloom depends on buds formed the previous summer, with new wood as backup, so a count from transplant would not describe how the plant behaves.
Will coffee grounds turn Penny Mac blue?
Unlikely to do it reliably. The pH shift from coffee grounds is very small, and the plant needs available aluminum, which acidity releases. Aluminum sulfate acidifies the soil, and blue shows below about pH 5.5.
Can I cut it back in spring?
You can, but you would remove buds formed last summer. Penny Mac reblooms on new wood, so it is not a total loss. Prune right after flowering, and check your state page for the timing.
Is it safe around pets?
Bigleaf hydrangea is documented toxic only when large quantities are eaten, and the source names cats, dogs and horses. It lists H. macrophylla as the only hydrangea with a documented toxicity, which describes what is on record, not a guarantee for other types.