Blue spruce: profile, planting & care
Its blue needles and beautiful, conical growth make the blue spruce a real eye-catcher. It is not only popular as an ornamental in the garden, but also as a Christmas tree at home.
The blue spruce (Picea pungens) is known as the Colorado spruce. It owes this name to its blue-green and extremely pointed needles. It delights with its uniform, harmonious shape – depending on the variety, it even works as a Christmas tree in the living room. In this article you will learn about the special properties of the blue spruce and how to plant and care for it properly.
Contents
Blue spruce: Origin and characteristics
Blue spruces belong to the genus of spruces (Picea) and to the pine family (Pinaceae). This wild species is native to the Rocky Mountains, where it can thrive at altitudes of up to 3000m. A wild blue spruce can reach a stately growth height of up to 20 m and a growth width of 8 m in suitable locations. However, there are also numerous dwarf forms of the blue spruce that, with a height of about 1.5 m, fit excellently in pots. Make sure the plant pot is as wide as possible, because the blue spruce is shallow rooted and needs enough space to spread out. Its shallow and extensive root system offers the spruce many advantages, especially in its native habitat: rainwater and washed-in nutrients are directly intercepted over a large area before they seep into the deeper layers of the earth. However, as the roots do not reach the groundwater, the blue spruce is dependent on regular rainfall. With age, the branches begin to droop and form an irregular, open tree crown.
The trunk of the blue spruce and branches that receive little light form a black-brown scale bark. Characteristic of the blue spruce is its resinous smell of the forest. With a winter hardiness of up to -30 °C, it can easily withstand the winter in central Europe and live for up to 400 years.
What do the cones of the blue spruce look like?
The hanging cones of the blue spruce appear at the beginning to end of May. Male flower cones are formed throughout the crown and appear in a yellow to red shade. They stand either in groups of 3 to 5 or individually at the tips of one-year-old shoots. Female flower cones are only developed in the upper crown and are coloured in a red to green shade. From them develop the seed-bearing and cylindrically shaped blue spruce cones, which grow between 6 and 11 cm long. These blue spruce cones hang for more than 1 year, so they can be seen in two different stages on the tree.
Blue spruce as a Christmas tree
The blue spruce is popular as a Christmas tree because its blue needles and dense growth create a Christmassy atmosphere. Thanks to its sturdy branches, it can carry Christmas decorations without any problems. Compared to other Christmas trees such as the red spruce or the Nordmann fir, it loses fewer needles.
The most beautiful varieties
Its regular and conical growth makes the blue spruce a popular ornamental in private gardens and parks. In the garden it is used as a solitary planting or windbreak. Nowadays, the blue spruce comes in numerous different varieties, which differ in needle colour, but also in growth. We present the most beautiful species and varieties:
- ‘Koster’: With its growing height of up to 15 m and a growing width of about 5 m, this blue spruce looks particularly good as a solitary in the garden. Its decorative needles are pointed and shiny silver-blue.
- ‘Oldenburg’: The needle dress of this blue spruce has an intense, steel-blue colour and is adorned with light brown cones in autumn. It reaches a compact growth height of about 8 – 15 m and a width of 5 – 7 m. Environmentally conscious amateur gardeners can buy spruces like the Picea pungens ‘Oldenburg’ in pots. The plant pot keeps it much smaller than it would be outdoors and it can even be used as a Christmas tree for many years – with occasional repotting, of course.
- ‘Glauca Globosa’: This variety develops a rather broad, dense and conical habit over time. It grows to a maximum of 2 m tall and 3 m wide, so it remains compact. Its needles are silvery blue in colour and about 10 – 12 mm long.
- ‘Glauca’: The blue spruce is characterised by its gigantic growth of up to 20 m in height and 8 m in width. It grows in a dense pyramidal form and takes on a harmonious shape in the garden. Its 20 – 30 mm long needles shine in a steel blue.
Planting blue spruce
The blue spruce thrives best in a sunny to light-shaded, cool place with acidic to alkaline and moderately dry to fresh soils. Subsoil that is too rich in nutrients or too heavy is not suitable as a site for the blue spruce. The blue spruce does not tolerate a place that is too hot and dry. To improve the humus content, for example, our peat-free Plantura Organic All Purpose Compost is ideal. It not only provides the blue spruce with nutrients, but also promotes healthy soil life, thereby offering the best conditions for good plant growth. The wood fibres contained in the substrate create a loose structure in the soil and provide enough space for the fine roots to spread more easily.
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The best time to plant the blue spruces is from September to October. Especially in the autumn months there are mild temperatures and the humid weather helps the plant to form new roots. Below we show step by step how best to plant the blue spruce:
Planting blue spruce in the bed
- Loosen the soil with a garden fork or similar item.
- Dig a planting hole twice as wide and deep as the root ball.
- Lay a drainage layer of gravel in soils that tend to compact.
- Then add up to 50 % planting soil to the planting hole, depending on the soil quality.
- Water the root ball of the blue spruce generously before planting.
- To stimulate root formation, lightly score the root system in 3 – 4 places with a knife or garden shears – but first ensure the potted plant is well rooted.
- Place the blue spruce in the planting hole at the correct height so that the trunk meets the ground and is slightly above the surrounding soil level.
- Fill in the planting hole with a mixture of excavated soil and planting soil and press down firmly
- Spread a layer of mulch about 5 – 15 cm high directly around the blue spruce
Planting blue spruce in a pot
- Choose a container that is at least 45 cm wide and has a water drainage hole.
- Spread a drainage layer of expanded clay on the bottom of the pot.
- Plant blue spruce in structurally stable and high-quality potting soil, such as our Plantura Organic All Purpose Compost.
- The substrate should be kept moist.
- Repot every 2 years.
Tip: Wear gloves when planting the blue spruce to protect yourself from the sharp needles.
The right care
There are small differences in care depending on whether the blue spruce is kept in a pot or in a bed.
Caring for blue spruce in the bed
Once the blue spruce has established itself in the bed, it does not need much care. For vigorous growth, it can be useful to fertilise the blue spruce. Fertiliser should be applied with a conifer fertiliser from March to April. To improve the humus content in the soil, for example, our Plantura All Purpose Plant Food is excellent. It provides the blue spruce with the perfect combination of nutrients and due to its animal-free, organic composition, this fertiliser is extremely environmentally friendly. Adding compost and mulching in spring can improve the humus content in the soil. The blue spruce does not need pruning, as it grows into a beautiful shape all by itself. Only dead wood and stunted branches should be removed, because the blue spruce does not sprout from old wood. The ideal time for this is early spring, before new needles sprout. If you want to use a few branches of the blue spruce for decoration at Christmas time, you should make sure that only the green shoots are cut and not the brown wood, in order to avoid holes in the tree crown.
Caring for blue spruce in a pot
A blue spruce in a pot should receive a high quality granular fertiliser, such as our Plantura Rose Food. This contains readily available nutrients and is rich in magnesium, which leads to healthy and vigorous growth. If the blue spruce will not be staying in the one plant pot for too long, our Plantura Liquid Houseplant Food ensures optimal nutrient utilisation of the substrate and supports nutrient uptake with living microorganisms.
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Tip: The blue spruce is often infested by the green spruce aphid and the little spruce sawfly. Brown discoloured needles can be an indication of a pest infestation. A tapping test is useful if an infestation with the green spruce aphid is suspected. To test, hold a very large bowl, a fine landing net or a cloth under the blue spruce and tap or shake the branches. Since the green spruce aphid expects danger, it will drop in response. If these aphids are present, they will find themselves on the laid out cloth. If there is an acute infestation, you should consult a specialist who is authorised to apply insecticides. Also check the location, as the blue spruce is particularly at risk of pest infestation in places that are too dry and windy.
Is the blue spruce poisonous?
The blue spruce is not poisonous to humans, dogs or cats. Caution is only required when handling the needles, as they are very sharp.
With its blue needle dress, the blue spruce is a beautiful ornamental tree in the garden, but also a decorative Christmas tree for the home. The Madagascar jewel (Euphorbia leuconeura) can also be an unusual and low-maintenance houseplant.
