How to Grow and Care for 'Blue Princess' Holly

'Blue Princess' holly is a female cultivar of the blue holly evergreen shrub and commonly used as a landscape specimen plant or hedge shrub. This holly variety grows in temperate climates, perennial to USDA zones 4-7, and in average, well-draining soils, enjoying full sun but also growing in partial shade.

The berries and leaves of 'Blue Princess' holly are are toxic to humans and pets.

'Blue Princess' Holly Care

Here are the main requirements for 'Blue Princess' holly:

• Choose a spot with plenty of sun, though a partial shade location can work.
• Prepare well-draining, slightly acidic soil that holds moisture.
• Water the plant regularly while it is getting established, then about once a week during the growing season.
• Avoid over-fertilizing 'Blue Princess' holly, as too much nitrogen in the soil can prevent it from fruiting.

Light

'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.

Soil

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.

Water

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.

Fertilizer

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.

Pruning

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:

1. Take a 6- to 8-inch softwood cutting about 1/4 inch below a leaf node, using sharp pruners.
2. Dip the cut end in rooting hormone.
3. Embed the cutting in a small pot filled with a mixture of potting medium and sand.
4. Keep the growing medium moist until a root system develops. This can take several weeks.
5. After roots have developed, transfer the new plant into a larger pot, or plant in the garden.

Overwintering

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

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.

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.
  

Bloom Months

'Blue Princess' Holly blooms in the spring, from April to May, leading to signature berries developing in the fall.

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:

Yellowing Leaves

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.

Leaf Drop

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.

Burned Leaves

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.

From: thespruce