Gadenin日本語Get the appThe one rule that governs everything
Agapanthus performs best when it is slightly crowded and slightly starved. Once you accept that, care becomes mostly a matter of what not to do. Do not pot it up when it looks tight. Do not feed it a general purpose fertilizer through the summer. Do not water it when it is dormant. Do not plant it into rich soil in the hope of a bigger display. Each of those well meant actions pushes the plant toward leaf growth and away from flowers.
The plant you are aiming for looks slightly uncomfortable. Roots visible at the surface of the pot, roots emerging from the drainage holes, a root ball so dense that when you knock the plant out of its container you see more root than compost. That is a plant about to flower well, not a plant in trouble. A pot that has been split by the pressure of its own roots is a familiar sight around a well flowered agapanthus and is nothing to be alarmed by.
Feeding: potash yes, nitrogen no
Feeding is the one place where active intervention genuinely helps, provided you feed the right thing. A high potash liquid feed, the kind sold for tomatoes, applied every two weeks from the point when new growth starts in spring until the flower buds show color, is the standard regime and it works. Potash supports flower and stem development. Nitrogen supports leaf development, which this plant already does far too enthusiastically.
A general purpose or lawn type feed, or a mulch of fresh manure, is actively counterproductive. It produces long, soft, dark green leaves that flop outward, hide any flowers that do appear, and go into winter full of water and vulnerable to frost damage. If you have been feeding a plant that way and it has stopped flowering, simply stopping and switching to potash often restores flowering within two seasons.
Stop feeding altogether once flowering finishes. The plant is heading toward its rest period, and late feeding pushes out soft growth at exactly the wrong time of year.
| Season | Water | Feed | Other work |
|---|---|---|---|
| Early spring, growth restarting | Start watering as new leaves appear, keeping the mix just moist | Begin a high potash liquid feed every two weeks | Pull back winter mulch, remove damaged leaves |
| Late spring to midsummer | Water freely in dry spells, allow the surface to dry between | Continue high potash feed every two weeks | Support tall stems in exposed positions |
| Flowering period | Keep water steady, do not let pots dry to wilting | Stop feeding once the buds show color | Remove stems as each head goes over |
| Late summer to autumn | Reduce watering gradually | None | Cut spent heads to the base unless saving seed heads |
| Winter, deciduous kinds | None once leaves have died back | None | Dry mulch over the crown, keep rain off pots |
| Winter, evergreen kinds | Just enough to stop the mix drying out completely | None | Move under cover before the first hard frost |
Watering by the season, not by the calendar
Agapanthus stores water in its thick fleshy roots, which makes it far more tolerant of drought than of waterlogging. In open ground an established clump rarely needs watering at all except in a long summer drought. In containers the picture is different, because a root bound plant in a small pot dries fast and a plant in flower is moving a lot of water up tall stems.
Through the growing season water a container plant thoroughly when the top inch (2.5 cm) of the mix is dry, then let it drain completely. Never leave the pot standing in a saucer of water. Wilting leaves in high summer mean genuine drought and should be corrected, but the plant recovers from that far more readily than from roots sitting in cold sodden compost.
From the end of flowering, taper off. A deciduous plant gets no water at all once the leaves have yellowed and collapsed, and its pot is best moved somewhere the rain cannot reach it. An evergreen plant needs only enough through winter to keep the root ball from drying to dust, which in a cool bright place under cover might mean watering once a month.
Leaves, stems and tidying
Routine tidying is light. On evergreen kinds pull away outer leaves as they yellow and brown, taking them off cleanly at the base rather than cutting halfway and leaving stubs. On deciduous kinds leave the dying foliage in place until it has fully yellowed, because the plant is drawing food back into the roots during that process, and then clear it away before winter so it does not sit wet over the crown.
Tall flower stems in windy or exposed positions can be supported with a discreet ring or a few canes and string set in place before the buds open, rather than after a stem has already keeled over. Stems that flop despite support are usually a symptom of too much nitrogen or too little sun rather than a lack of staking.
Handle the plant with gloves. Agapanthus sap contains irritant compounds that cause itching and, if transferred to the eyes, real discomfort. This matters most when tidying old leaves or cutting stems, when sap runs freely.
Keep a simple record and stop guessing
Because agapanthus responds slowly, over seasons rather than weeks, memory is a poor guide to what is actually working. Note the date you begin and end feeding, what type of feed you used, and the date the first flower stem appears each year. Note also the year each plant was last repotted or divided, and the pot size it went into.
Those few lines answer the questions that otherwise recur every summer. Is this clump flowering later than last year? How many years has it been in this pot? Did the switch to a potash feed actually change anything? A plant with four years of notes behind it is far easier to diagnose than one with none, and the notes cost you a minute a season.