Gadenin日本語Get the appThe pot is the single biggest decision you make
Almost every complaint about agapanthus refusing to flower traces back to the moment it was planted. The plant comes out of a small nursery pot looking cramped, the grower feels sorry for it, and it goes into something twice the width with a generous helping of rich compost. Two years later there is a magnificent arching mass of strap leaves and not one flower stem. That is not bad luck. It is the predictable result of giving the plant exactly what it does not want.
Agapanthus sets flower buds when its root system is under mild pressure and its food supply is modest. A congested root ball with roots circling the wall of the pot and pushing out of the drainage holes is the normal, healthy, flowering state for this plant. Loose roots running freely through fresh compost tell the plant it has room to expand, and it responds by expanding, which for a strap-leaved perennial means leaves.
So choose a pot only one size up from the one the plant arrives in, or none at all. A container two inches (5 cm) wider than the root ball is ample. Terracotta suits it better than plastic because the walls dry faster between waterings and the weight stops a tall head of flowers from tipping the whole thing over in wind.
| Decision | What to do | What happens if you overdo it |
|---|---|---|
| Pot width | No more than 2 inches (5 cm) wider than the root ball | Roots spread freely for years and flowering is postponed |
| Potting mix | Loam based compost with a third coarse grit added | Peat rich mixes stay wet and rot the fleshy roots in winter |
| Fertilizer at planting | None, or a light scatter of a high potash granular feed | Nitrogen rich compost or manure gives lush leaves and no stems |
| Depth of the crown | Crown just at the surface, roots covered, growing points visible | Buried crowns rot in wet winters and flower late or not at all |
| Ground spacing | 18 to 24 inches (45 to 60 cm) between clumps | Wide spacing delays the crowding that triggers flowering |
| Aspect | Full sun, at least six hours a day | Shade produces long floppy leaves and thin, few stems |
Ground planting: drainage first, fertility last
In open ground the same logic applies with one addition. Agapanthus has thick, fleshy, water-storing roots that tolerate summer drought remarkably well and rot readily in cold wet soil. Winter wet kills more plants than winter cold does. Before you plant, look at the ground after a heavy downpour. If water sits on the surface for more than an hour, either raise the bed or plant somewhere else.
Fork the top ten inches (25 cm) and work in coarse grit or sharp sand if the soil is heavy clay. Resist adding manure or rich compost. What you are aiming for is a soil that drains fast and holds only moderate fertility, which is close to a poor sandy loam. A gravel bed, the top of a low retaining wall, a south-facing slope or the strip along a warm path all suit it.
Set the crown level with the surrounding soil, spread the fleshy roots outward rather than coiling them, and firm gently. Water once to settle the soil around the roots, and after that treat the new planting as established. Agapanthus does not need coddling once its roots are in contact with soil.
- Check drainage before anything else Dig a hole a foot (30 cm) deep, fill it with water and let it drain, then fill it again. If the second filling has not gone within four hours the site is too wet for agapanthus in winter. Raise the planting six inches (15 cm) above the surrounding soil or move to a container.
- Loosen deeply, enrich lightly Fork the top ten inches (25 cm) and mix in grit if the soil is heavy. Add no manure. If the ground is genuinely impoverished a scatter of a balanced granular feed at half the packet rate is enough for the whole first season.
- Plant with the crown at the surface Make a hole wide enough to spread the roots out sideways and shallow enough that the crown, the point where roots meet leaves, sits exactly level with the soil. Draw soil back over the roots only, leaving the growing points visible.
- Space for crowding, not for comfort Set clumps 18 to 24 inches (45 to 60 cm) apart in a group of three or more. They will grow into each other within a few seasons, and that congestion is what brings a mass of stems rather than an occasional one.
- Water once, thoroughly, then leave it One long soaking settles the soil and removes air pockets. Afterwards water only in a prolonged dry spell during the first summer. Routine watering of an established planting is unnecessary and encourages soft growth.
- Mark the position of the crowns Deciduous kinds vanish completely in winter and are easy to fork through or plant over. Push in a short cane or a label at each end of the group and note the count so you can tell in spring whether every crown has come through.
Evergreen or deciduous decides where the plant lives
Before you commit a plant to open ground, work out which of the two broad groups you have, because it changes everything about siting. The evergreen kinds keep their broad strap leaves all year, are the more tender group by a wide margin, and are damaged or killed by hard frost. The deciduous kinds die back to nothing in autumn, hold narrower leaves in growth, and are considerably hardier, surviving in the ground in climates where an evergreen would not last a winter.
The practical rule is simple. If your plant still has leaves in the depths of winter, treat it as a container plant that comes under cover when frost threatens. If it retreats underground each autumn, it is a candidate for a permanent bed outdoors with a dry mulch over the crown. Planting an evergreen in a cold open border is the second most common way to lose agapanthus, after drowning it in winter wet.
The sap of agapanthus irritates skin and eyes, and the roots and leaves are toxic if eaten. Wear gloves when dividing or handling cut roots, wash your hands afterwards, and keep discarded pieces away from children and pets.
What the first two years should look like
A newly planted agapanthus, whether from a pot or a division, commonly skips flowering in its first season and sometimes its second. That is normal and is not a sign that anything is wrong. What you should see in year one is a steady increase in leaf number and a root ball that resists a gentle tug. Flowers arrive once the roots have filled the space available, which is precisely why the space should be small.
The mistake to avoid in this waiting period is intervention. A plant that has not flowered by its second summer does not need a bigger pot, richer compost or more water. Almost always it needs more time, more sun and less kindness. Give it a high potash feed in spring rather than a general purpose one, keep it where it gets sun for most of the day, and wait.
Write down what you planted and where
Record three things at planting and you will save yourself years of guessing. First, the date and the position of each crown, with a rough sketch or a count per group, so that a dormant deciduous clump is not accidentally dug up. Second, the pot size used, because when a plant finally flowers you want to know exactly how tight the roots were when it happened. Third, whether the plant was evergreen or deciduous, since that single fact determines every winter decision you make for the next decade.
In the seasons that follow, add the date the first flower stem appears and the number of stems per clump. Those two numbers, tracked over three or four years, tell you plainly whether the clump is still building up, is at its peak, or has finally become congested enough to need dividing.