Agapanthus: How to Plant Them

Where to plant agapanthus?

Agapanthus can be grown in open ground, in flower beds, or in pots, for example on a balcony or terrace.

If you grow them in open ground, plant them in rich soil, slightly moist but above all well-drained. They dislike waterlogged conditions, which can cause root rot. If your soil is heavy and clayey, it is advisable to add sand or gravel to improve drainage. In regions with mild climates, they can be planted directly in the ground, where they will thrive with the space needed to develop their root system.

If you live in a region with cold winters or are growing non-hardy varieties, container planting is recommended. This will allow you to bring them indoors to protect them from winter frosts. Use a large pot, as agapanthus roots like plenty of room to grow. Ensure the pot has good drainage by placing a layer of clay pebbles or gravel at the bottom, then fill it with a mix of compost and sand to ensure good root aeration.

The hardiness of agapanthus varies by variety. Some can withstand winter temperatures as low as -10°C or even -15°C.

To learn how to identify the hardiest agapanthus, check out Michael’s advice in the article: “Hardy Agapanthus for Northern Climates?”

For abundant and vigorous flowering, agapanthus need a sunny and warm location, with at least 6 hours of direct sunlight per day. Avoid planting them in areas where water may pool, such as hollows or low-lying spots in the garden. Whenever possible, opt for planting on higher ground, on a slope or mound, to reduce the risk of excessive moisture in winter.

When to plant agapanthus?

It is best to plant agapanthus in spring, in March or April, when the frosts have passed and the soil warms up. This allows the roots to establish well before summer.

Autumn planting can be considered in regions with mild winters, but it is riskier, as moisture and cold can damage young plants. If planting in autumn, make sure to protect your agapanthus with mulch and ensure the soil is well-drained.

How to plant them?

In the ground:

• Dig a planting hole at least 3 to 4 times wider and deeper than the plant’s root ball. This will allow the roots to spread easily and establish well.
• If your soil is heavy or clayey, replace the excavated soil with an equal mix of compost and sand to improve drainage. In well-drained soil, simply adding compost will suffice.
• Return this mixture to the hole, ensuring the roots are covered with at least 10 cm of good soil. The plant’s crown should sit slightly below the soil surface but not be buried too deeply.
• After planting, water generously to firm the soil around the roots. Then, water regularly during the growing period, about twice a week, especially in dry weather. Be careful not to let water stagnate, as agapanthus dislikes excess moisture.

In pots:

• Use a large pot at least 30 cm deep and wide, as agapanthus roots appreciate space.
• Place a layer of clay pebbles, gravel, or pottery shards at the bottom of the pot to ensure good drainage and prevent waterlogging.
• Fill the pot with a mix of 50% compost and 50% horticultural sand to ensure good root aeration.
• Plant your agapanthus, then fill in with a little more substrate.
• Water generously to firm the substrate around the roots.

How to care for them?

Watering agapanthus should be regular, especially during the growing season. For plants in the ground, water about twice a week, ensuring the soil remains moist but not waterlogged, as agapanthus dislike stagnant moisture. For potted plants, watering should be more frequent, particularly in summer, as soon as the compost begins to dry out. It’s important that water drains well, and you should always empty the saucer to prevent roots from sitting in water.

In spring, applying a potassium-rich fertiliser encourages abundant flowering. During the blooming period, a liquid feed every two weeks can support the plant’s efforts. After flowering, we recommend cutting back spent flower stalks at ground level to prevent the plant from wasting energy on seed production. In winter, if the leaves turn yellow, you may trim them for a tidier appearance, but leaving the foliage can also be beneficial as it helps protect the plant from cold.

In regions with cold winters, a thick mulch around the base of in-ground agapanthus is advisable to shield the roots from frost. Materials such as dead leaves or straw work well. From autumn onwards, reduce watering, as agapanthus are particularly sensitive to excess moisture in winter. For potted plants, it’s best to move them to a frost-free location, such as an unheated greenhouse or garage. If this isn’t possible, wrapping the pot with horticultural fleece or hessian can help protect the roots.

Every 3 to 4 years, dividing agapanthus clumps helps rejuvenate them and prevents overcrowding. This process stimulates flowering and also provides an opportunity to propagate new plants. Division is best carried out in spring or autumn.