Knotweed rounds off the creative garden design decoratively in perennial beds, along shrubs or on the banks of the pond. The perennial of the year 2012 convinces with a long flowering period, robust winter hardiness and frugal undemanding. Read here how easy it is to plant and care for it.

Knotweed is a fragrant beauty that spreads very quickly

Table of Contents

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  1. Plant knotweed correctly
  2. care tips
  3. Which location is suitable?
  4. The right planting distance
  5. What soil does the plant need?
  6. What is the best planting time?
  7. When is flowering time?
  8. Cut knotweed correctly
  9. Pour knotweed
  10. Fertilize knotweed properly
  11. hibernate
  12. multiply knotweed
  13. How do I plant correctly?
  14. Knotweed in the pot
  15. Is knotweed poisonous?
  16. Which knotweed species are suitable for the garden?
  17. How do I keep creeper knotweed under control?
  18. Beautiful varieties

    19. Plant knotweed correctly

    When planting, pay attention to the remarkable vigour, which characterizes numerous knotweed species. To prevent the perennial from conquering the garden, mighty bush and candle knotweed or mighty creeper knotweed should be planted with a root barrier. A large stone bucket or mason's vat without a bottom is suitable, for example, as well as the rot-proof geotextile specially developed for this purpose. (107.71€) Proceed with these steps:

    • Place the root ball of the still potted young plant in water
    • Dig a large planting pit and spread out potsherds or grit (€46.95) at the bottom as drainage
    • Enrich the excavation with compost and horn shavings (32.93€).
    • If necessary, install the root barrier that makes sense for large species
    • Plant the potted knotweed up to the lower pair of leaves and water

    With the root barrier, make sure that the knotweed has a sufficient substrate volume that is twice as large as the root ball. A mulch layer of leaves, grass clippings or bark mulch has a beneficial effect on growth.
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    care tips

    Planted in a sunny to partially shaded location in humus-rich, nutritious and freshly moist soil, a knotweed only requires the following care measures:

    • Water regularly when the substrate surface has dried
    • Cut back to the first pair of leaves after flowering
    • Covered with a mulch for winter protection in rough locations
    • Wrap the bucket with foil and set it on a block of wood
    • Water on a mild day when there is a clear frost

    If at all, knotweed gets a starting fertilization in March/April. A cut back close to the ground should only be done in late winter so that the foliage provides additional protection for the root ball during the cold season.
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    Which location is suitable?

    Knotweed feels best in a sunny to partially shaded location. The perennial is completely happy when the soil is rich in nutrients, humus and fresh and moist. Mighty herbaceous lilacs, such as the Johannis cloud, lose stability in wind-exposed locations. The candle knotweed comes with maximum location tolerance, which thrives in any location as long as it is not bothered by waterlogging.

    The right planting distance

    The ideal planting distance depends on the selected species and variety. Creeping snake knotweed does best at a distance of 35 cm from its neighbor, while the popular candle knotweed should be planted at a distance of 90-100 cm. A majestic flowering tower like the lilac should not get closer than 150 to 200 cm to its plant neighbors.

    What soil does the plant need?

    The best knotweed species and varieties for the private ornamental garden are largely in agreement with regard to the requirements for the soil. They would like to spread their roots in nutrient-rich, humus-rich and above all fresh and moist soil. Irrespective of this, the genus comes up with specialists for extreme locations, such as the water knotweed, which thrives wonderfully even in the permanently wet soil of a pond bank.

    What is the best planting time?

    For young plants in containers, planting time in the garden is from spring to autumn. A date between mid-May and mid-June or in early autumn to the end of September is advantageous for growth and vitality. During hot, dry days in midsummer, planting will only be successful if an adequate water supply is guaranteed.

    When is flowering time?

    The main flowering period of knotweed is from June to September. In mild spring weather, the herbaceous lilac puts on its flowers as early as mid-May, closely followed by the knotweed in June. If you don't get tired of their fragrant flowers, you can add the variegated knotweed and stringy knotweed, which bloom from September to October and end the garden year with a furious autumn colour.

    Cut knotweed correctly

    If the withered inflorescences take on an unsightly appearance, the scissors are used for the first time. After flowering, cut knotweed back to the top leaves on the stem. Leave the rest on the perennial until early spring as natural winter protection. Then use the pruning shears a second time to trim the plants to just above the ground.
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    Pour knotweed

    Knotweed is dependent on a generous water supply when it is dry. Sometimes even a rain shower doesn't penetrate through the dense pile of leaves and flowers. Therefore, check the substrate every 1-2 days and water when the surface has dried.

    Fertilize knotweed properly

    There is such powerful growth power in knotweed that no fertilizer is needed in nutrient-rich soil. In poor locations and in the event of deficiency symptoms, apply a starter fertilizer in March/April. A portion of mature compost with horn shavings is just as suitable as a small dose of complete fertilizer.

    hibernate

    Most knotweed plants are hardy. In rough locations and in planters, we still recommend the following protective measures for reasons of caution:

    • Do not cut back knotweed completely before winter
    • Pile the plant up thickly with leaves and cover with needle brushwood
    • Cover the bucket with bubble wrap, place on wood and cover the substrate with straw

    A large number of popular knotweed species are sensitive to frost. Therefore, water the plant on mild winter days when there is no snow.

    multiply knotweed

    Knotweed can be easily propagated with cuttings. In early summer, select a semi-lignified, non-flowering shoot and cut off a 10-15 cm section below a leaf node. Defoliated except for the upper pair of leaves, plant two-thirds of the cutting in a poor substrate, such as pricking soil or peat growing medium. Then it goes on like this:

    • Place a perforated plastic bag over each pot
    • Keep the substrate constantly moist in a semi-shady, warm location
    • Air the cover daily to prevent mold

    After 3-4 weeks, a knotweed cutting will have enough roots to be planted in the bed or bucket.
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    How do I plant correctly?

    Thanks to its natural growth power, a knotweed usually tolerates a change of location without damage. In early spring after pruning, cut off the root ball all around in the radius of the growth height. The subsequent digging up can be associated with a high fitness effect due to the powerful root system. Do not leave any severed pieces of root in the ground, because knotweed will sprout from them in no time at all.

    At the new location, the planting pit should be prepared and the excavation should be enriched with compost. Maintain the previous planting depth and water generously and regularly on the day of transplanting and afterwards.

    Knotweed in the pot

    In the pot, knotweed transforms the balcony into a blooming summer oasis. For vital growth and lush flowering, only a few aspects of care need to be heeded:

    • Spread a drainage of potsherds under the potting soil to protect against waterlogging
    • Never allow the substrate to dry out
    • Cut back to the first pair of leaves in autumn
    • Cover the bucket with foil in winter, place it on wood and cover the substrate with leaves

    In spring, cut back the overwintered knotweed close to the ground and repot the plant in fresh, nutrient-rich substrate. With this procedure, the additional administration of fertilizer is not necessary.

    Is knotweed poisonous?

    There can be no talk of toxicity in knotweed. On the contrary, our ancestors recognized its usefulness as a medicinal and food plant. The tannins in the rootstock heal unpleasant diarrheal diseases, while the tender leaves and shoot tips make a delicious spring vegetable.
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    Which knotweed species are suitable for the garden?

    Vigorous knotweed species, such as the creeper knotweed and the Japanese knotweed, brought the genus into disrepute as ruthless invaders. Today the tide has changed, because the species, which grow in a disciplined manner and bloom lavishly, have attracted the attention of hobby gardeners. A selection of magnificent knotweed for the garden at a glance:

    • Candlestick Knotweed: delicate flower clusters above 40 cm long, heart-shaped foliage; sprawling growth up to 150 cm in height
    • Snail knotweed: creeping species with compact growth and 20-30 cm high inflorescence; the ideal ground cover
    • Variegated knotweed: enchanting foliage in autumn under white panicles of flowers for shady locations
    • Bush knotweed: known as the shrub lilac, thanks to its bushy habit up to 200 cm and lush flowering bushes from May

    The water knotweed can hardly be topped in terms of location tolerance. This species thrives both in water and on land and tolerates summer drought as well as waterlogging.
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    How do I keep creeper knotweed under control?

    Thanks to its rapid growth rate, creeper knotweed quickly greens meter-high facades with a climbing plant and transforms fences into an impenetrable privacy screen. Since the plant will not stop growing on command once the desired size is reached, proper precautions in planting and care are important. Things to watch out for:

    • Plant creeper knotweed with a stable root barrier
    • Attach the climbing aid at a distance of at least 10 cm from the facade to avoid damaging the wall
    • Maintain a distance of 150 cm from downpipes, lightning conductors or gutters

    Above all, keep the climbing plant in check with a courageous pruning. In February or March, radically cut back a creeper knotweed. In normal garden soil, no fertilizing is necessary, because the plant grows up to 30 cm a day even without additional nutrients.
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    Beautiful varieties

    • Johannis Cloud: majestic herbaceous lilac with white blossom clouds and a growth height of up to 200 cm
    • Superbum: expansive knotweed for planting along the banks of large ponds with pink flowers from June to October
    • Red Dragon: Spectacular variegated knotweed with bright purple-red foliage and silvery V markings
    • Taurus: Abundantly blooming candle-knotweed with rich red flowers and stable stability despite a growth height of 100 cm
    • Darjeerling Red: charming snail knotweed for flat carpets of flowers all summer long

Category:

Herbs