How to plant window boxes and hanging baskets with annuals in plug plants?

Choosing the right container

The collections from Promesse de Fleurs made up of 5 plug plants are suitable for filling 60 cm long window boxes or 40 cm diameter hanging baskets and round containers. Always check that the chosen container has drainage holes at the bottom. These drainage holes will allow excess water to escape. If not, especially in the case of a vintage or reclaimed container, drill holes using a drill or a pointed tool and a hammer.

Ensure that the container has proper drainage holes

Fill the planter with potting soil

Always choose a quality compost suitable for this use, such as a “compost for planters” or a “compost for geraniums and flowering plants”. Avoid “universal” composts or those at very low prices.

It is also not recommended to reuse compost from the previous year. Too compacted and depleted of nutrients, it would not allow for good growth of your plants. However, you can reuse it in the garden as an organic amendment where it will help lighten the soil.

Fill your container with compost. If your planter contains bulbs for spring, stop halfway, place the bulbs point up, then continue filling the container to 1 cm from the edge. Tap several small sharp knocks on the walls of the container to slightly compact the compost and achieve a well-levelled surface.

Fill the planter with compost

Note:
Some composts contain a water retainer that limits the frequency of necessary watering. If not, you can add Stockosorb at a rate of 30 grams per 10 litres of compost. Do not exceed the dose: excessive water retention could lead to root asphyxiation.

Mix a water retainer like stockosorb into your compost if it doesn’t already contain it

Dispose the plug plants

Remove the plug plants from their recycled plastic sleeves. Check that they are moist; if not, soak them in water at room temperature. Never replant a dry plug plant!

Open the sleeve and identify the varieties. Ensure that the plug plants are moist; if not, soak them in water.

Some young plants from cuttings, such as geraniums, have their root ball wrapped in paper. You can remove it or leave it on, but if you leave it, make sure it does not stick out of the compost after planting. Arrange the plug plants in a staggered pattern, at equal intervals across the surface of the pot.

Arrange the plug plants in a staggered pattern, 15 cm apart.

Plant and pinch the young plants.

Plant the plug plants one by one. Make a hole with your finger, push the plug plant in, and firmly pack the compost around the young plant with your fists.

Make a hole with your finger, plant the plug, then firmly pack the compost around the young plant

For more harmonious growth, it is highly recommended to “pinch” the tips of the young plants (between your thumb and index finger or using a well-sharpened pruning shear) to stimulate the branching at the base of the plant for well-filled window boxes.

Pinch the young plants to stimulate the branching of the plants

Fertilise and water

Unless your potting mix already contains it, provide a slow-release fertiliser that will be effective throughout the season, such as the Osmocote® Exact 6-month cones. Simply push them into the potting mix 1 to 2 cm below the surface. You need one cone for an area of 15×15 cm, which means 1 cone per pot with a diameter of 15 to 20 cm, 2 cones per pot of 22 to 26 cm, 3 cones per pot of 27 to 32 cm, or for window boxes: 2 cones per 30 cm in length. Finally, water thoroughly with a fine spray to avoid damaging the young plants, until water flows from the drainage holes.

Water thoroughly with a fine spray

⇒ Discover our advice sheet: which fertiliser for potted plants and window boxes?

Cultivation and care

Young plug plants are professional products that require careful attention to ensure a good start!

• If you have planted annual flowers, place your planters in a bright room in the house or in the conservatory, at a temperature not falling below 12-14 degrees, for 3 to 6 weeks. Water regularly without excess, the surface of the compost should dry a few millimetres between each watering. Move them to their final location when the last risks of frost have passed, between early and late May depending on the regions. In the city, you can generally move them out earlier than in the countryside due to the heat island effect.
• If you have planted planters of biennials, you can leave them outside, always in a bright location but sheltered from the scorching midday sun, while waiting for them to grow and for their spot to be freed up from summer planters!

To go further

Discover our advice sheet: How to create beautiful flower hangings?