Plant biennials in plug plants

Where to plant?

Biennials can be planted both in the ground and in pots, depending on the available space and the desired decorative effect.

If you wish to plant biennials in window boxes or pots, it is important to choose a location that is both bright and sheltered. Ideally, place them in a spot that receives several hours of direct sunlight each day, such as a south or west-facing balcony. Biennials appreciate light for their growth, but they should not be exposed to strong winds or harsh weather conditions for extended periods.

As for containers, opt for window boxes or pots that are deep enough (at least 20 to 30 cm) to allow the roots to develop properly. Ensure that the pots have drainage holes to prevent water accumulation, as biennials do not like waterlogged soil.

Finally, remember to space the plug plants adequately in your window boxes to allow for good air circulation and to avoid competition between the plants, which will encourage generous flowering.

In the ground, biennials thrive in well-drained, light soils rich in humus, but without excess moisture, especially in winter. They flourish both at the edge of borders and at the base of trees, where they benefit from dappled light. For good flowering, choose a sunny or lightly shaded location, but sheltered from cold winds. They can also be planted in rockeries or along paths, where natural drainage and exposure to gentle light will ensure optimal development.

In which soil or compost?

In containers and window boxes, we recommend using a goodpotting soil for flowering plants that is well-draining (for example, with plenty of bark or perlite) and enriched with fertiliser with slow release, such as those available commercially. Don’t hesitate to add a layer of clay balls or gravel at the bottom of the container to improve drainage.

In the garden soil, choose a spot with light to medium soil, amended with a bit of potting soil if necessary. Using a garden rake, crumble the soil well to loosen it and add a base fertiliser at planting (dried blood, for example).

Use quality potting soil that is both draining and rich

When to plant them?

Plant the biennial plug plants as soon as they arrive, ideally in September-October, in containers and window boxes or directly in the ground in finely prepared and enriched soil. If the intended location is not yet ready or if the conditions are not favourable for planting (heavy rain or soil too dry), you can grow them on in buckets for 4 to 6 weeks.

How to plant?

• Prepare window boxes by filling them with potting soil, or if planting in the ground, prepare and enrich the soil.
• There may be paper surrounding the plug plant of your plants: you can remove it beforehand, but it is not essential.
• Plant ensuring that the top of the plug plant is level with the potting soil, covered by just a few millimetres of substrate. Firmly press down with your fingers around each plug plant, ensuring the young plant remains upright.
• For optimal effect in pots, troughs, window boxes, and hanging baskets, stagger the plants, spacing each one 10 to 15 cm apart in all directions. Thus, 5 plants are suitable for a window box approximately 40 cm long or a pot 30 cm in diameter. In borders, biennials can be spaced 15 to 25 cm apart.
• If you wish to combine biennials and bulbs that flower in spring, first plant the bulbs at a depth of 3 times the height of the bulb, then the plug plants on the surface.
• Water generously at planting and during the following weeks, as the plug plants can dry out quickly. However, be careful of excess water! Ensure to use containers with drainage holes and empty the saucer 10 minutes after watering.

Note: some varieties of biennials delivered as plug plants, such as Erysimum, primroses, some Violas, Arabis, Carex… are perennials and can be replanted in the garden in borders after flowering.

Combine biennial plants with perennials for a very aesthetic result

How to care for them?

One of the key points for successfully planting biennials in plug plants is managing watering. During the first few weeks after planting, it is essential to water regularly to ensure the roots establish well. Remember to water even during winter if it does not rain or if the container is placed in a sheltered spot from precipitation. Be vigilant if they are in pots or containers, as the substrate dries out much faster than in open ground. Do not water during frost. In spring, make regular fertiliser applications (about once a month) to support flowering.

Remove faded flowers as they appear to encourage prolonged flowering.

Biennials are not very susceptible to diseases, but they can sometimes be subject to attacks from aphids or powdery mildew, especially if humidity is high. In this case, use a natural insecticide or black soap to prevent spreading.