Herbaceous lupins are hugely popular clump forming perennial plants much admired in early summer in herbaceous borders countrywide. Although they have been created over generations by intricate hybridisation work to create the colours we admire today native lupins were originally bred from shrubs or sub-shrubs in dry hilly areas of the Mediterranean, North Africa and the Americas.
Herbaceous lupins are fully hardy and fully deciduous. They are greedy clump forming plants which thrive in rich soils with the addition of well-rotted dung or leaf mould and benefit from a top dressing of mulch in spring or when they go dormant in the autumn. Lupins grow best in full sun in a light well drained soil. They hate moist boggy situations where they may get bacterial rot or mildew on the leaves.
The secret to keeping your lupins thriving, healthy and developing more new flower heads each year is really very simple. After the flowers have finished and lost their colour cut off the whole flowering stem down as close to ground level as you can reach. This is even more important if your plants are grown in pots. Removing the whole flower spike avoids the plant wasting energy on creating and setting seeds in the large pea like seed pods which form so quickly after flowering. The plant will then divert its energy and resources to creating fresh new shoots at the base of the plant from which more vigorous flower spikes will appear next year.
Certainly slugs are a major problem in late spring when your plants start to grow away. You must decide whether to use slug pellets then before and after wet spells, or if you prefer, to use more natural methods of containing these pests. It is usually the tiny slugs which live below ground level that do the real damage overnight and not the huge ones you see with a slime trail. Rabbits also enjoy the young lupin leaves and can be a problem in the nursery where we need to remember to erect the tunnel rabbit guards each night.
Lupins can readily be propagated from fresh growth basal cuttings taken in early spring. Lupins are some of the easiest seeds to grow when sown in semi trays also in spring. However, if you do collect seed from your own plants, do not expect it to come true if you have lots of different varieties in different colours in your garden.
Tree lupins or Lupinus arboreus are short lived plants originating from California which are more or less evergreen. They need no special treatment like the herbaceous ones and often grow best and most vigorously in poor soils on bare earth banks or the uncultivated edges of your garden. L. arboreus normally has pale yellow flowers but there are forms with white and blue flowers. All these plants quickly naturalise and you certainly do not need to remove the seed heads. In prime situations these tree lupins can grow up to 6ft with a similar spread before dying of exhaustion after only a few years or a very cold winter.