Lupine Care: Why Feeding Makes Them Worse and What They Actually Need

The plant makes its own nitrogen, so stop feeding it

Lupines are legumes. Lift one carefully and you find pale nodules along the roots, each a colony of bacteria converting nitrogen from the air into a form the plant can use. A settled lupine is not competing for soil nitrogen in the way a delphinium or a phlox is; it is manufacturing its own supply and, incidentally, leaving some behind for its neighbors.

Feed it anyway and you get the classic result: enormous soft leaves, thick sappy stems that flop in the first storm, and spikes that are shorter and fewer than on the unfed plant beside it. Soft growth is also exactly what lupin aphid colonises first, so a well-fed lupine tends to be the one that gets covered while the lean one next to it stays clean.

So do not give lupines a general fertilizer, and keep manure and rich compost away from the root area. If the soil is genuinely exhausted, a light dressing of something low in nitrogen with potassium in it, applied once as the flower buds form, is the most that is ever useful. On any reasonable garden soil the correct amount of feed is none.

The same logic applies to the mulch. Use grit, leaf mold or bark rather than well-rotted manure, and pull it back an inch or two from the crown so the base of the stems stays dry.

A lupine that flops, produces huge leaves and short spikes is almost never underfed. It is overfed, or in too much shade, or both. Cutting the feeding is a faster fix than staking.

Drainage and soil first, everything else second

The taproot goes straight down and stays there for the life of the plant, which means the soil eighteen inches (45 cm) below the crown matters more than the surface. If that layer holds water through winter the root rots, and the plant that came through last year perfectly simply fails to appear in spring. Nothing you do at ground level compensates.

Aim for a light, sandy or gritty soil that never puddles, neutral to slightly acid. Lupines are genuinely unhappy on chalk and thin limey soils, where the leaves go yellow between the veins while the veins stay green, growth stalls and the plant lingers for a year or two before dying. If that is your ground, grow them in large deep containers with an acid or neutral mix instead of fighting the bed.

On heavy clay, plant on a raised ridge or a slight mound and work grit into a wide planting hole rather than a narrow one. A narrow hole backfilled with grit in clay becomes a sump. Widening the improved area, or accepting that the plant will be a three-year visitor rather than a long resident, are the two honest options.

Full sun is the default. Lupines tolerate a few hours of shade and often prefer light afternoon shade where summers are hot, but a plant in real shade leans, produces thin pale spikes and is far more prone to mildew.

Watering, mulching and staking without overdoing any of them

An established lupine reaches water most perennials cannot, and in an average summer it needs nothing from you. Water it in a genuine drought, when the lower leaves start to dull and hang, and then water properly: a long soak that wets the top eight to ten inches (20-25 cm), rather than a daily sprinkle that keeps the crown damp and the deep root dry.

The exception is the year of planting and the weeks either side of flowering. A young plant has not yet got its taproot down and will die of drought in a fortnight. A mature plant running dry while it is building spikes aborts the top half of the buds, giving you a short spike with a bare tip.

Two inches (5 cm) of grit or leaf mold over the root area, kept off the crown, does more than any watering routine. It keeps the deep soil evenly moist, keeps the surface dry enough to discourage slugs, and holds down annual weeds around a plant you should not be hoeing near.

Tall spikes catch wind, and a heavy one going over in a summer storm often snaps at the base rather than bending. Put supports in while the leaves are still low, so the stems grow up through them. Individual canes tied loosely just below the spike work for a few plants; a ring or a cage of twiggy sticks is quicker for a group. Staking after a plant has flattened never looks right and usually breaks something.

Watch weekly, cut hard, and plan the replacement

Once a week from the time the buds show, part the leaves and look at the top of each stem and the underside of the young leaves. Lupin aphid builds a colony from nothing to a spike encrusted gray in under a week, and the difference between a plant you rescue with a hose and a plant you lose is whether you looked on the Monday or the Sunday.

As each spike fades, cut it off at once, taking the stem down to a leaf or to the base. Left on, it sets a heavy crop of pods and pours the season's reserves into seed, which shortens the plant's life and prevents the second flush that deadheading usually brings.

After the last flowers, if the foliage is tired or mildewed, cut the whole plant down to two or three inches (5-8 cm). It regrows a clean rosette within a few weeks and goes into winter with fresh leaves rather than a mat of infected ones. In autumn cut everything back and clear the debris away from the crown rather than leaving it as a mulch.

Accept from the start that this is a short-lived perennial. Three good years, sometimes four or five on very well drained ground, and then a crown that comes up thin and flowers poorly. Rather than nurse it, take basal cuttings from your best plants each spring and sow a small batch of seed each year, so a replacement is always a season ahead. Write down when each plant was set out, how tall its spikes were and how many it carried each year, and the moment a plant is past its best is obvious rather than a guess.

Do not try to rejuvenate an old lupine by digging and dividing it like a clumping perennial. The taproot will not take it. Cuttings off the crown in spring, or fresh seed, are the only ways forward.