The gladiolus (correct plural gladioli in Britain, gladiolus in North America and elsewhere), is named from the bud-tip that breaks through the foliage and resembles the short broad blade of the Roman soldier’s and gladiator’s sword.
What is planted is not a bulb, but a corm, in which all parts of the eventual plant are present in embryo. Choose, therefore, large high-crowned corms feeling heavy for their width and with a small basal plate (root scar) underneath, indicating that they are young and vigorous. Ensure that these get a good start and are well fed from the beginning, since the number of buds to a spike is determined quite early. Grown mainly as cut flowers and for garden decoration, they vary from little over 1 in. to about 7 in. across the bloom.
Soils and Situations
Gladioli will grow on most soils, but prefer a medium to light well-drained loam with plenty of humus and some rich, moisture-retaining material from 1 ½ -2 ft. beneath the surface.
Preferably, they should be sited where there will be full sun for most of the day and not close to trees or hedges.
Where and How to Grow
In the herbaceous border they make good tall plants, not merely for the back, but to vary the centre. Here the foliage-fans create useful green verticals, even when the plant is not in flower. Attractive patterns may be made by placing one central corm with a circle of from five to nine around it on a 6-9-in. Radius. Diamonds of from three to five corms a side are effective; a small diamond inside a larger is even better.
For continuous planting, avoid the straight line in favour of a zigzag of three to five corms to each ‘tack’. Where there is sufficient room, three zigzags consisting of tall large-flowered at the back, medium-flowered ‘Butterflies’ and ruffled in the middle, and the dainty primulinus hybrids and ‘Face-ups’ in front would give more continuity of colour.
Tubs or small beds may be planted with circles and diamonds, but tubs should be at least 15 in. deep. Underplanting with the usual range of low summer-flowering bedding plants works well, as they feed at a different level. Never let the tubs dry out, but ensure there is ample drainage.
For cutting
For cut flowers, gladioli are best grown in rows in the vegetable garden. Early saladings can be sown between corms (radishes, globe beets, cos lettuce, spring onions, short carrots). These are harvested before the gladioli need all the space between them.
Preparing the site
Dig in the autumn, working plenty of water-holding material into the second spit or immediately below it. Rotted farmyard manure is best; but mature compost, leaf-mould, sedge-peat, or anything organic and moisture-retentive will do. Gladioli like good drainage about the corms, but plenty of moisture at the roots. For the smaller types, heavy feeding is not required.
Gladioli grow best in neutral or slightly acid soil, so do not over-lime. In March make holes about 3 ft. apart throughout the patch, sprinkle a little naphthalene in, and cover immediately. The fumes will drive out wire-worms.
Avoid planting where potato ellworm is known to be present, as these attack the corms and their roots. Douse the whole area with a weak solution of disinfectant, to which a liquid slug-killer may be added. Then sprinkle dry slug-bait around the pot.
Planting
Grow your gladioli in blocks of three or four rows each, with a 2-ft. Path between for ease of access. The spacing between rows should be sufficient for easy hoeing, not less than 7 in. Larger-flowered kinds should be set about 9 in. apart, medium-flowered 6 in., small-flowered, primulinus, and nanus hybrids, 4 in. Plant throughout April and May. For the closely placed ones, dig a narrow trench about 6 in. deep.
For the widely spaced ones it is quicker to trowel out holes; never use a pointed dibber that will create an air-pocket beneath the corm, as well as compacting the soil. On medium soils there should be 44-5 in. of soil above each full-sized corm, on light soils 5-5 in., on heavy soils 4 in.
Have a bucket of sharp fine sand to hand, into which has been thoroughly mixed a fungicide and an insecticidal dust. Dust trenches or holes with bonemeal or steamed boneflour to promote root development. Then place a handful of the sand mixture where each corm is to sit, press the corm firmly into this, and pour a second handful over it. This ensures good drainage around the corm, easy, dry lifting, and a protective barrier against below-soil pests and fungus growths. Fill the hole with crumbled, stone-free soil.
Before planting each corm, strip any remaining leaf-husks and examine the top. If you want the maximum number of spikes with a multiplication of corms harvested, leave all the little growing ‘eyes’ intact and be careful not to damage them when pressing the corm into the sand. If you want one straight spike, especially for exhibition purposes, rub out all but the most central ‘eye’. NEVER plant corms that are stone-hard, or squashy, or with large patches of brown, or with concentric circles of black where the old leaves joined. These will infect other stock with disease.
After-care
Hand weed close to the plants in moist conditions; hoe between the rows in dry weather. Mulching will reduce this labour, help the soil to retain heat and moisture, and suppress weeds. Mulch after the plants are showing and the larger-flowered kinds have been given a side-dressing of an organically-based fertilizer. Uproot entirely and destroy any gladioli showing yellow leaves with still-green veins. These are harbouring Fusarium oxysporum, which is incurable.
Watch for budtips to appear and see these grow clear of the foliage without getting crooked. Stake with bamboo canes in wind-swept areas and always for the larger-flowered varieties, as soon as the direction of facing can be determined by the forward bend of the flowerhead. Tie in with soft material.
Cutting
Cut in the early morning when the first bloom is partly or fully open, using a sharp knife down inside the foliage and then slanting it through the stem, to leave at least four leaves intact. Treat the plant as a growing entity, so that about six weeks later you may lift the new corm plump and healthy.
Lifting
Trim off all roots and foliage immediately and dry the corms thoroughly and quickly. A fortnight later the old corms will pull cleanly away from the new ones, which should be cleaned, further dried, dusted with an insecticide and fungicide mixture, and stored cool (but above freezing-point) where there is air circulation (dry) and preferably in the dark.
