Allelopathic crops
How can allelopathic crops and ground cover help keep weeds under control?
In plants, the term allelopathy is generally used to describe the process by which plants release phytotoxic compounds (allelochemicals) into the soil environment, which have a harmful effect on neighbouring plants and prevent other plants from growing.
What is allelopathy useful for?
1/ Allelopathy can help reduce the use of herbicides.
Biochemical compounds present in almost every tissue of the plant (roots, stems, leaves, flowers, fruit) are released either directly (root exudation, volatilisation) or indirectly through the breakdown products of residues (leaves, roots). Allelopathic compounds affect fundamental plant processes such as photosynthesis, hormone balance, protein synthesis, chlorophyll production, plant-water relations, germination and nutrient uptake.
2/ Allelopathy can help reduce the use of insecticides: these compounds reduce attacks by certain pest insects.
Since plants cannot move, allelopathic compounds would appear to be a defence developed by the plant world in response to attack by parasites and predators, or simply to the competition between species for water, light and nutrients.
We have selected plants according to a number of criteria:
- The size required (carpeting, low, medium)
- Drought tolerance
- Hardiness
ACHILLEA crithmifolia
Yarrow
A perennial with finely cut blue-green leaves that persist through winter. A very dense ground cover that tolerates being walked on.
Max. drought months: 2.5 months
pH: tolerates chalk
Soil: any
Density: 4 per m²
Ornamental feature: downy grey-green foliage
Interest: tolerates moderate foot traffic
Foliage: evergreen
Flowering period: June to July
- creamy white
- 5 to 15cm
- full sun
- -15°C
POTENTILLA verna
Spring cinquefoil
This common, early-flowering species is happy in dry meadows and on sunny banks. It is a plant with spreading-erect hairs. In summer the sterile shoots lengthen and put out roots. The leaves are divided into five toothed leaflets. The yellow petals are fairly well spaced, leaving the sepals clearly visible.
Max. drought months: 3 months
pH: tolerates chalk well
Soil: light
Density: 6 per m²
Ornamental feature: dark green foliage
Interest: tolerates moderate foot traffic
Foliage: evergreen
Flowering period: March to April
- bright yellow
- 5 to 10cm
- full sun
- -15°C
THYMUS serpyllum
Wild thyme
Wild thyme is an aromatic plant that is very widespread in the south of France. Its flowers are pink, grouped in rounded heads. The leaves are elliptical and slightly fringed with hairs. As well as its culinary qualities, thyme is a natural antiseptic and tonic.
Max. drought months: 2.5 months
pH: tolerates chalk well
Soil: light
Density: 4 to 6 per m²
Ornamental feature: dark green foliage
Interest: tolerates moderate foot traffic
Foliage: evergreen
Flowering period: June to July
- pink
- 5 to 10cm
- full sun
- -15°C
ACHILLEA umbellata
Umbellate yarrow
This small ground-covering Achillea forms evergreen cushions of downy silver foliage. It produces white flowers in umbels and is drought tolerant.
Max. drought months: 4 months
pH: tolerates chalk well
Soil: light
Density: 9 per m²
Ornamental feature: bright silvery-grey foliage in winter, turning almost white in summer
Interest: tolerates moderate foot traffic
Foliage: evergreen
Flowering period: April to May
- white
- 10 to 15cm
- full sun
- -15°C
CENTAUREA bella
Knapweed
A perennial with grey-green foliage, silvery underneath, forming a rounded cushion.
Max. drought months: 4 months
pH: tolerates chalk well
Soil: light
Density: 6 to 9 per m²
Ornamental feature: grey-green foliage with silvery undersides, deeply cut, nectar-rich
Interest: tolerates moderate foot traffic
Foliage: evergreen
Flowering period: March to May
- pink violet
- 10 to 15cm
- full sun or partial shade
- -15°C
HEDERA helix Shamrock
Ivy
A miniature ivy with small, three-lobed, glossy green leaves.
Max. drought months: 4 months
pH: tolerates chalk well
Soil: light
Density: 1 per m²
Ornamental feature: Glossy green leaves and black fruits that attract birds in winter
Interest: tolerates moderate foot traffic
Foliage: evergreen
Flowering period: September to October
- yellow
- 10 to 20cm
- full sun or partial shade
- -15°C
JUNIPERUS horizontalis Blue Chips
Creeping juniper Blue Chip
A conifer with a very spreading habit, eventually forming a dense carpet 30 cm thick. Very straight, thread-like shoots, blue, turning violet-purple in winter.
Max. drought months: 4 months
pH: tolerates chalk well
Soil: any
Density: 1 per m²
Ornamental feature: Evergreen grey-blue leaves taking on violet tints in winter
Interest: Allelopathic ground cover, banks
Foliage: evergreen
Flowering period:
- 15 to 20cm
- full sun
- -15°C
JUNIPERUS communis Green Carpet
Common juniper
A carpeting, compact conifer with greyish dark green foliage, turning violet-blue in winter.
Max. drought months: 4 months
pH: tolerates chalk well
Soil: any
Density: 1 per m²
Ornamental feature:
Interest:
Foliage: evergreen
Flowering period:
- 20cm
- full sun
- -15°C
LAVANDULA x chaytorae Richard Grey
Grey lavender
A compact plant with evergreen leaves, grey to almost white and woolly in appearance. Very fragrant flowers in short spikes, deep violet.
Max. drought months: 4 months
pH: tolerates chalk well
Soil: poor, stony or sandy, perfectly drained
Density: 6 per m²
Ornamental feature: Compact growth forming a spreading cushion
Interest: Containers, gravel gardens, allelopathic ground cover
Foliage: evergreen
Flowering period: Late June to early August
- Blue-purple
- 20 to 30 cm
- full sun
- -12 to -15°C
TANACETUM densum subsp. Amanii
Armenian tansy
Native to Turkey and Syria (limestone rockeries and scree), Tanacetum densum subsp. amani is an excellent ground cover for the dry rock garden. A charming plant, it unfurls finely chiselled evergreen foliage of a beautiful silver colour and, over time, takes on the look of a small ground cover.
Max. drought months: 4 months
pH: tolerates chalk well
Soil: free-draining
Density: 6 to 9 per m²
Ornamental feature: Silvery grey, evergreen, finely toothed
Interest: Rockeries, paving, allelopathic ground cover
Foliage: evergreen
Flowering period: June to July
- Yellow
- 15 cm
- full sun or partial shade
- -15°C
VINCA major
Greater periwinkle
Greater periwinkle is the perfect choice for excellent ground cover in shade or partial shade: it spreads quickly and lasts for years. In spring it forms a beautiful dense carpet of periwinkle-blue flowers over a bed of glossy mid-green foliage. Undemanding, it is happy in moist soil but also in dry soil under trees.
Max. drought months: 2.5 months
pH: tolerates chalk well
Soil: any
Density: 2 to 3 per m²
Ornamental feature:
Interest: Banks, large woodland ground-cover plantings, allelopathic gardens
Foliage: evergreen, glossy green
Flowering period: March to April
- Blue-purple
- 30 cm
- full sun or shade
- -15°C
VINCA minor
Lesser periwinkle
Lesser periwinkle is, as its name suggests, shorter than greater periwinkle and produces smaller flowers. It remains the perfect choice for excellent ground cover in shade or partial shade: it spreads quickly and lasts for years. In spring it forms a beautiful dense carpet of small periwinkle-blue flowers over a bed of glossy mid-green foliage. Undemanding, it gives its best results in light, fairly moist soil.
Max. drought months: 3 months
pH:
Soil: ordinary, dry to moderately damp
Density: 6 per m²
Ornamental feature: The plant spreads slowly by means of stolons that root where they touch the soil.
Interest: woodland ground cover, allelopathic gardens
Foliage: glossy dark green
Flowering period: May to September
- Blue, violet and white
- 10 to 15 cm
- full sun or shade
- -15°C
BALLOTA hirsuta
Hairy horehound
An evergreen perennial with woolly, lime-green leaves. The plant forms a rounded, compact ball, especially if pruned after flowering.
Max. drought months: 5 months
pH: tolerates chalk well
Soil: light, well drained
Density: 2 to 3 per m²
Ornamental feature:
Interest: Gravel gardens, banks, large ground-cover plantings, allelopathic gardens, seaside gardens
Foliage: glossy dark green
Flowering period: June to July
- Pink-tinged white
- 60 cm
- full sun
- -10°C to -12°C
CISTUS x florentinus Tramontane
...
This hybrid has dark green foliage and carpeting, dense, well-branched growth, making excellent ground cover.
Max. drought months: 4 months
pH: tolerates chalk well
Soil: poor, stony or sandy, perfectly drained
Density: 2 to 3 per m²
Ornamental feature: Used in large plantings, this plant needs little weeding thanks to its allelopathic properties
Interest: Gravel gardens, banks, large beds, ground cover, allelopathic gardens, seaside gardens
Foliage: dark green
Flowering period: April to May
- White
- 30 cm
- full sun or partial shade
- -12°C to -15°C
CISTUS x pulverulentus Sunset
Pink rock rose
This variety is remarkable for its Indian-pink flowers with golden centres. Its cup-shaped flowers, about 4 cm across, are renewed from June to October and cover the shrub, especially early in the season. Rock roses have very fine, distinctive petals, often crumpled, resembling tissue paper.
Max. drought months: 4 months
pH: tolerates chalk well
Soil: poor, stony or sandy
Density: 1 per m²
Ornamental feature:
Interest: Shrub beds, banks, large beds, ground cover, allelopathic gardens, seaside gardens
Foliage: grey-green
Flowering period: May to July
- pink dark
- 40 to 60 cm
- full sun or partial shade
- -12°C to -15°C
LAVANDULA x intermedia Grosso
Lavandin
A vigorous, compact lavender.
Max. drought months: 4 months
pH: tolerates chalk well
Soil: poor, stony or sandy
Density: 1 to 2 per m²
Ornamental feature: Ash-green foliage, abundant and fragrant mauve-blue flowers.
Interest: Containers, perennial and shrub beds, herb gardens, gravel gardens, allelopathic gardens
Foliage: grey-green
Flowering period: June to July
- 30 to 60 cm
- full sun
- -15°C
MYRTHUS communis Giulli
...
A miniature, compact and very decorative variety.
Months of drought tolerated: 4 months
pH: tolerates chalk well
Soil: poor, stony or sandy
Density: 6 to 9 per m²
Ornamental feature: A remarkable miniature variety with tiny leaves packed tightly together
Interest: Containers, rockeries, allelopathic gardens
Foliage:
Flowering period:
- 30 to 40 cm
- full sun
- -10°C to -12°C
SANTONIA chamaecyparissus
Cotton lavender
A branching, bushy subshrub. The stems are covered with small, narrow, toothed, whitish leaves clothed in silvery down. In summer it bears heads of small golden-yellow flowers.
Max. drought months: 5 months
pH: tolerates chalk well
Soil: poor, stony or sandy
Density: 2 per m²
Ornamental feature:
Interest: Banks, perennial and shrub beds, allelopathic gardens
Foliage: evergreen
Flowering period: June
- golden yellow
- 60 cm
- full sun
- -12°C to -15°C
LOMELOSIA minoana
...
The seed heads, which stay on the plant all summer long, form a very decorative mass.
Max. drought months: 4 months
pH: tolerates chalk well
Soil: poor, stony or sandy, perfectly drained
Density: 2 per m²
Ornamental feature: Rich in nectar, the flowers are attractive to butterflies
Interest: Banks, perennial and shrub beds, large ground-cover plantings, allelopathic gardens, seaside gardens
Foliage: silvery grey
Flowering period: March to July
- soft mauve
- 60 cm
- full sun
- -10°C to -12°C
ROSMARINUS officinalis Corsican Blue
Creeping rosemary
A creeping rosemary with an arching habit, dark green foliage that is grey underneath, and large violet-blue flowers. It flowers abundantly.
Max. drought months: 4 months
pH: tolerates chalk well
Soil:
Density: 0.5 to 1 per m²
Ornamental feature: A variety with an irregular, more or less spreading habit
Interest: Containers, shrub beds, banks, large ground-cover plantings, allelopathic gardens
Foliage: dark green
Flowering period: March to July
- dark blue speckled with mauve
- 60 to 80 cm
- full sun
- -10°C to -12°C
CISTUS x purpureus
Purple rock rose
A rounded shrub with reddish shoots. It produces terminal cymes of three crumpled, deep pink flowers with purple-brown blotches at the base.
Max. drought months: 5 months
pH: tolerates chalk well, but may become chlorotic on heavy soil
Soil: poor, stony or sandy, perfectly drained
Density: 1 per m²
Ornamental feature:
Interest: Banks, shrub beds, allelopathic gardens, seaside gardens
Foliage: dark green
Flowering period: April to May
- violet-pink with purple-red blotches
- 1m to 1.25m
- full sun or partial shade
- -12°C to -15°C
MYRTUS communis subsp. Tarentina
Tarentum myrtle
Evergreen dark green leaves. White flowers followed by blue-black fruit in autumn and winter.
Max. drought months: 4 months
pH: tolerates chalk well; resistant to sea spray
Soil: light, well drained
Density: 1 per m²
Ornamental feature: Can be used in a variety of situations, for example as topiary, as a low edging or in an informal hedge
Interest: Containers, shrub beds, informal hedges, seaside gardens
Foliage: green
Flowering period: July to September
- white
- 1 to 2m
- full sun or shade
- -10°C to -12°C
PHLOMIS fruticosa
Jerusalem sage
A rounded shrub with upright stems. Its leaves resemble those of sage: grey-green and woolly underneath. Its whorls of flowers are a deep golden yellow.
Max. drought months: 5 months
pH: tolerates chalk well; resistant to sea spray
Soil: light, well drained
Density: 1 per m²
Ornamental feature: Self-seeds readily in the garden
Interest: Shrub beds, seaside gardens, allelopathic gardens
Foliage: grey-green
Flowering period: April to May
- bright yellow
- 1 to 1.50m
- full sun
- -10°C to -12°C
