Blue rhombus, silver shrub, perovskia – care and pruning

The blue rhomb, also known as silver bush or perovskia, likes a warm location in full sun, which is also sheltered from the wind. South-facing places in the garden, which can offer many hours of sunshine per day, are best suited. It also grows in partially shaded places, where the flowers are usually a little less abundant. Blue diamonds are quite soil tolerant and have few demands:

• normal garden soil
• well permeable to water
• dry to moderately moist
• little nutrients (poor soil)
• also thrive on stony and sandy soils
• also calcareous soils
• no heavy soils and waterlogging

The more sun the blue rhombus gets and the more calcareous the soil, the more intense the leaf color. Blue diamonds not only feel particularly comfortable with bush males, lilacs or shrub roses, but they also come into their own in their company. Blue diamonds are also ideal as a container plant for the terrace or balcony. They even feel very comfortable on hot south-facing balconies, where other plants can quickly burn or die of thirst due to the strong sunlight and the heat.

plant

Blue diamonds grow into spherical low shrubs of around 50 to 100 centimeters, with a large part of the growth height being due to the long, blue-violet flower spikes. This gives the popular and easy-care plants a feathery and light appearance. Together with other grasses or plants that love drought, they can be cultivated in rock gardens, on slopes or in otherwise barren landscapes. Since the blue rhomb forms only very shallow roots, no large planting hole is necessary. Even so, the soil should be prepared a little:

• very sandy soils: mix in a little loam.
• Damp soils: dig the planting hole deeper (30-40 centimeters) and create a drainage layer with at least ten centimeters of expanded clay or small stones.
• very nutritious or rich soils: mix a good portion of sand under the soil.

Even individual plants are particularly eye-catching. If you want to put several blue diamonds in the bed, you should not underestimate their rapid growth. Planted too densely, the spherical growth is lost and the individual plants take away each other’s light.

• Row planting: a maximum of two to three plants per meter
• Area planting: a maximum of five plants per square meter

pour

The water requirement of the blue diamonds is rather low. They prefer dry soils that drain the water well. Both in the garden soil and in the tub, the plants therefore only need water when it is very dry and can easily get by for several days without watering. Pouring is always moderate, because the otherwise robust plants do not like waterlogging at all.

Fertilize

Fertilizing is similar to watering: Excessive nutrient levels in the soil damage the blue rhombuses more than they do. Therefore fertilization should be avoided almost completely. If they grow on very poor subsoil, the single application of a complete fertilizer in April makes it easier to drive them out. Compost or manure should not be worked into the soil in the planting area of ​​blue rhombuses.

To cut

A blue rue should never be cut back in autumn, but only in early spring. Because the own foliage forms a good natural frost protection for the plant. Before the first warm days in March, when the plant comes to life again and sprouts again, pruning takes place radically. If shoots have died due to the frost or if they are kinked by other influences, they are removed at the same time. The flowers only form on the young wood of the subshrub, so it needs this annual pruning in order to fully sprout again and to develop a lush bloom. If the blue-rhombus is not regularly and strongly cut back, it tends to become bald in the lower area. It will then also not be as beautifully bushy and have significantly fewer flower spikes.

• radical pruning from the end of February to mid-March
• Shape: Straight to slightly hemispherical
• Cutting height: just above the ground
• leave only the woody shoots (15-20 centimeters)

Keeping the blue rhomb in shape
The shrub with its gray-silvery leaves grows very loosely with its long flower spikes. In strong winds or rain it can happen that it loses a bit of shape in its unprotected location and parts of the shoots remain on the ground. In order to direct it back into a spherical-bushy shape and to straighten the outer shoots, the gardener can wrap it relatively loosely in the lower area with bast. However, this should only be done very carefully so that it is not restricted in its natural growth and beauty.

Multiplication by sharing

If the blue rhomb has grown into a stately shrub, it can easily be propagated by dividing it. This form of reproduction is also known as vegetative reproduction. Two plants emerge that do not differ from one another in terms of their genetic make-up.

• Time: In spring (after the ice saints in mid-May) or in autumn (right after flowering)
• Share only large, healthy plants.
• Use the sharp spade to pierce the center of the root ball in the soil.
• Alternatively: dig up the plant and cut through the root ball with a sharp, clean knife.
• Remove dead shoots and roots.
• Insert in a new place (check location and soil conditions).
• Water lightly for better growth.

Many plants develop root runners by themselves after a few years. These can then be separated and are able to survive as an independent plant.

Propagation by cuttings

Plants are able to regenerate themselves by being able to rebuild dead or lost organs. In horticulture this behavior is used for vegetative reproduction. This creates a new plant that is identical to the mother plant.

Shoots are cut off and planted in spring to allow the blue rue to propagate using cuttings. When the annual radical pruning is due after the frost period, there is also a good opportunity to pull cuttings. This method is very simple, but often fails. Therefore, when propagating by cuttings, a few rules should be observed so that the success rate increases:

Annual shoots that are slightly woody at the interface are usually cut as cuttings. In the upper area of ​​the shoot there must be at least two buds (leaf eyes) or two leaf bases. If there are leaves just above the cut, they are carefully removed. More than three leaves should not be left, because then the cutting will evaporate too much water that it cannot absorb again without roots.

• Choose strong shoots.
• Three to five leaf roots should be recognizable (eyes or leaves).
• Remove remnants of flowers.
• Carefully remove the leaves in the lower third (two pieces).
• A maximum of three leaves remain on the cutting.
• Carefully scrape off the bark over the cut with a sharp knife.
• Put in a protected place in moist garden soil
• Location: bright (without direct sunlight)

If the planting site in the garden is not chosen appropriately, the temperatures are too warm or too cold for the time of year, the sensitive cuttings often find it difficult to take root. Alternatively, of course, the cuttings can be pulled out on the windowsill. A bright place without direct sun at an east-facing window is ideal for this.

• Place the cuttings in moist soil in a plant pot or in an indoor greenhouse.
• Soil: cactus soil or potting soil with sand, germ-free
• Put the leafless lower third into the earth.
• Cover the pot with transparent foil or a bag.
• poke a few small holes in the bag
• Remove the film and ventilate at least once a day
• Occasionally spray with stale water.

The cuttings need a very high level of humidity to begin with. To increase this locally, transparent plastic bags or drinking glasses are suitable, which are placed with the opening facing down on the soil in the plant pot. However, you should not forget to remove the bag for a few minutes once a day. Not only does the plant need fresh air, ventilation also prevents fungus or mold from spreading. The best way to tell that some roots have already formed is that the cuttings are setting new shoots.

Overwinter

Blue diamonds, also called Russian sage, are perennial plants that are frost-hardy in our latitudes and are well suited for gardening in rock gardens, aromatic gardens or as an ornamental shrub. However, they need their own leaves to protect against frostbite. If the foliage remains on the plant and is not cut back in autumn, the blue rue can often survive frosts unscathed. However, the winter hardiness of the shoots is not really certain. In severe winters, the plant usually freezes back to the woody shoots on the ground. Although the above-ground parts of the plant die off, the blue-rue will sprout again in spring if it is severely cut back. Only in the first few years, when the plant may still be very delicate, should be piled up a little with dry leaves on the rhizome. Alternatively, a careful covering with brushwood is also possible. Piling up with leaves or soil does not harm older plants either, but is no longer essential for survival.

Diseases and pests

Blue diamonds are considered to be very robust shrubs that almost never fall ill in optimal locations with lots of sun, a water-permeable soil and protection from extreme weather conditions. If the conditions are not optimal, they tend to rot if there is too much water in the soil. A sparse or long growth indicates too little light. Then the bloom is also less abundant. Only when the plant is weakened is it susceptible to pests or diseases. So if an infestation with pests or fungi is recognizable or the blue rue is not growing or blooming well, the location or the soil quality should be checked urgently. It may be necessary to move it, but sometimes digging up and laying a drain is sufficient.

Conclusion
Blue diamonds are among the robust, low shrubs that do not require extensive maintenance. Even with little moisture, they produce lush blue-violet flowers. They are not only a visual enrichment for the garden, but also smell very aromatic. All you need is a very warm, sunny place in the garden that is sheltered from the wind and offers nutrient-poor, well-drained soil.