'Blue Princess' holly (Ilex × meserveae 'Blue Princess') is a female cultivar of the blue holly evergreen shrub and commonly used as a landscape specimen plant or hedge shrub. When pollinated by its male counterpart, 'Blue Prince', it produces bright red berries in the wintertime and is frequently used as a winter holiday decoration.
'Blue Princess' has a moderate growth rate compared to other hollies, adding one to two feet per year. Its leaves are glossy, dark green with a bluish cast and moderately spiny. The inconspicuous flowers bloom in the spring and are followed by bright red berries that remain on the shrub into winter. The best time for planting is in the early fall, though spring planting can also work in colder regions. Warm climates benefit from fall planting, so the roots have time to develop before the summer heat arrives.
This plant has berries that are mildly toxic to humans and pets.
|Common Name||Blue Princess holly, blue holly|
|Botanical Name||Ilex x meserveae 'Blue Princess'|
|Plant Type||Shrub (broadleaf evergreen)|
|Mature Size||10–15 ft. tall, 8–10 ft. wide|
|Sun Exposure||Full, partial|
|Soil Type||Moist, well-drained|
|Soil pH||Acidic, neutral (5.0—7.0)|
|Hardiness Zones||3b-7a (USDA)|
|Native Area||Nursery hybrid|
|Toxicity||Mildly toxic to people and pets|
Blue Princess Holly Care
Ilex x meserveae shrubs are dioecious plants, meaning that individual shrubs have flowers that are either male or female, but not both. These hybrid shrubs are sold under various male and female cultivars. 'Blue Prince' is a male pollinator paired with the female version, 'Blue Princess.' Only 'Blue Princess' can develop the trademark holly berries, and it needs pollination from a male holly shrub to do that. For abundant berries, you should have at least one male per three to five female shrubs.
'Blue Princess' can be sensitive to cold winter winds in zones 3 through 5, where winter protection is a good idea. When planting, add a layer of mulch to keep the shallow roots cool and to retain soil moisture. Besides making sure your shrub is getting enough water and doing a bit of pruning, this is a fairly low-maintenance plant.
'Blue Princess' holly will grow in full sun to partial shade. In the warmer parts of its hardiness range, it should have protection from the harsh afternoon sun.
Well-drained soil is key for these shrubs. They can tolerate a range of soil types and prefer a slightly acidic to neutral soil pH, 5.0 to 7.0.
Deeply water on a regular basis to keep the soil evenly moist in the shrub's first growing season. This will establish an extensive root system. After that, weekly waterings will usually be fine if you haven't had rainfall, though the shrub might need more frequent waterings in extreme heat. Just make sure it's never waterlogged.
Temperature and Humidity
The lowest temperatures this plant can endure are about -20 to -10 degrees Fahrenheit. Prolonged exposure to unseasonable heat or cold can weaken or kill it. Mulch can help to insulate the roots against temperature extremes. It's also ideal to plant the shrub somewhere that is sheltered from harsh, drying winter winds. A moderate humidity level is ideal.
Minimal fertilizer is required for this shrub. In fact, too much nitrogen in the soil can keep 'Blue Princess' from fruiting. Use an organic fertilizer made especially for holly, following label instructions. It's also beneficial to mix compost into the soil at the time of planting.
Types of Blue Holly
The "blue" in blue holly derives from the blue tint of the dark green leaves. Besides Blue Princess and Blue Prince, there are several other female and male blue hollies, including:
- 'Blue Girl' (Ilex x meserveae 'Blue Girl'): This holly is notoriously hardy, growing in zones 5 to 9. It reaches around 6 to 8 feet high and produces bright red berries.
- 'Blue Boy' (Ilex x meserveae 'Blue Boy'): This is the male counterpart to 'Blue Girl'. It won't produce berries, but its dark foliage works well as a dense hedge.
- 'Blue Maid' (Ilex x meserveae 'Blue Maid'): 'Blue Maid' is a fast-growing holly shrub that reaches around 8 to 10 feet high with a 6- to 8-foot spread. It also produces red berries and is hardy in zones 5 to 9.
- 'Blue Stallion' (Ilex x meserveae 'Blue Stallion'): 'Blue Stallion' is a fast-growing male pollinator hardy in zones 5 to 9. It grows to around 10 to 12 feet tall, and its foliage is a shiny dark blue-green.
- 'Hachfee' (Ilex x meserveae 'Hachfee'): A female plant also known as 'Castle Spire' grows 8 to 10 feet high and 4 feet wide.
- 'Heckenstar' (Ilex x meserveae 'Heckenstar'): The male plant for Hachfee is also known as 'Castle Wall'. It grows 8 to 10 feet tall and 4 feet wide as a dense shrub.
While it is possible for 'Blue Princess' holly to reach 15 feet high, these shrubs are easily kept at a fraction of that height with just minimal pruning. The best time to prune holly depends on aesthetics. Some gardeners prune in early winter because they want to bring the cut stems with their holly berries indoors to use as decorations. Others prune later in the winter because they prefer their display of holly berries to be outdoors on the shrubs.
Unless you are using them in a hedge, these shrubs look best when the pruning is not too obvious. To accomplish this, stagger the depth of your cuts. Hollies bloom on old wood produced the previous growing season. So remember that the later you prune, the fewer flowers and berries will be produced the following year. Balance this factor with your desired size and shape when choosing how much to prune, and when to do it.
Propagating Blue Princess Holly
All species of holly propagate reliably from cuttings taken in the late spring or early summer. Here's how to do it:
- Take a 6- to 8-inch softwood cutting about 1/4 inch below a leaf node, using sharp pruners.
- Dip the cut end in rooting hormone.
- Embed the cutting in a small pot filled with a mixture of potting medium and sand.
- Keep the growing medium moist until a root system develops. This can take several weeks.
- After roots have developed, transfer the new plant into a larger pot, or plant in the garden.
How to Grow Blue Princess Holly From Seed
Seed propagation is not recommended because it is an extremely long process. Planted seeds take more than a year to germinate and sprout, so it is rarely done outside the commercial trade.
Holly shrubs can be subject to desiccation during the winter, especially for young plants in the northern part of the hardiness range. While it's possible to spray the shrubs with an anti-desiccant in the late fall, most growers choose to protect vulnerable shrubs with burlap wrapped around a framework of stakes to protect them from harsh winter winds. For 'Blue Princess' holly, growers in zone 4 and 5 should consider some form of winter protection.
Common Pests & Plant Diseases
Common insect problems include holly leaf miners, spider mites, whiteflies, and scale.
- Leaf miners cause yellow and brown trails through the leaves. Treat this problem with a foliar pesticide labeled for control of leaf miners
- Spider mites cause speckling and discoloration of foliage. Spray the plant with insecticidal soap to control the pest.
- Scale is evidenced by tiny soft cottony patches or hard crusty patches on the leaves. Treat scale insect infestations by spraying with horticultural oil. Spraying will be most effective if applied early, while eggs can still be killed.
Disease issues include a variety of fungal problems, including powdery mildew, leaf spot, and tar spot. Powdery mildew causes a fine powdery residue on leaves, while the other fungal diseases cause small yellow, black, or white spotting on the leaves. All these problems can be treated with spray fungicides, but you can prevent the disease by providing plenty of air circulation and sunlight to the plants. Water at the base of the shrub rather than with overhead spraying to reduce fungal spore transmission.
How to Get Blue Princess Holly to Bloom
With Blue Princess holly the goal is not flowers, but fertilized flowers that will lead to attractive red berries. If your shrubs are not producing berries, there are two likely reasons:
- Your shrub is not being pollinated by a male plant: Try planting a clearly identified male 'Blue Prince' holly in the general area of your 'Blue Princess' shrubs. To ensure berries, you should plant one male shrub for every four or five female shrubs.
- Your shrub is being pruned too aggressively, at the wrong time. This holly blooms on old wood, which means that any harvesting of branches in the winter for decorative displays will remove established growth that would produce flowers and berries the following year. Try reducing how much you harvest—or omit cutting altogether—for a full year to see if your shrub responds by producing flowers and berries.
Common Problems With Blue Princess Holly
Holly shrubs are often entirely trouble-free, but when problems do occur, they tend to be one of the following:
Because hollies prefer acidic soil, they can develop chlorosis or yellowing of the leaves in soil with an alkaline pH. Feeding with an acid fertilizer can counteract this if you have highly alkaline soil. Mulching with pine needles can also help acidify the soil.
A holly that begins to drop its leaves is probably suffering from a leaf spot fungus. if the leaves are falling, it's probably too late to treat the fungus, but don't worry too much, because the plant usually recovers. Prevent future episodes by regularly treating the shrub with a fungicide.
Browned leaves and dead branches are most commonly caused by winter injury. Remove the dead leaves and trim back the branches to green wood. Prevent future injury by protecting the shrub through the winter with a burlap wind block or by spraying with anti-desiccant.
How long does a 'Blue Princess' holly shrub live?
With proper care and growing conditions, most holly shrubs are capable of living 100 years or more. The 'Blue Princess' and 'Blue Prince' cultivars were developed in 1973, and some of those first shrubs are still thriving.
How was blue holly developed?
An amateur gardener named Katherine Meserve, after moving from Manhattan to Long Island, longed for a true cold-hardy holly, She landed upon the idea of hybridizing Ilex aquifolium with I. rugosa, a hardy Japanese species. Her experiments eventually led to an entire line of cold-hard blue hollies, which was soon adopted by the commercial trade and led to a number of named cultivars between 1964 and 1973. The botanical name for these plants, Ilex x meserveae, was assigned in recognition of her contribution.
How do I tell the difference between a male and female holly shrub?
If your shrub is producing the hallmark red berries, then you know it is female. But a shrub that is not producing berries might still be a female plant, but one that is not being pollinated by a male plant. To tell the difference, you'll need to look closely at the flowers, which normally bloom in May. Male flowers will have protruding stamens extending from the center of the flower, while female flowers have no stamens, but instead have a green or red bump or cone (the ovary) in the center of the blossom.
Ilex x meserveae. North Carolina State Extension Plant Finder