Gladiolus are, in many ways, like the summer tulip and are no more difficult to grow. They make wonderful cut flowers and growing gladioli is easy. Like all good garden bulbs, if you get them growing in the ground they will flower.
Soil and Site
On rich but well-drained soils, you can plant them straight out in the garden. On my heavy clay – particularly in a wet spring – I tend to plant my glads in pots and put them out in a clump already growing.
Plant the corms 10cm (4in) apart and 10-15cm (4-6in) deep. Secured deep in the ground, you are less likely to need a stake.
In the garden
Gladioli need plenty of water to flower well, so if you can, dig a trench and pile in well-rotted manure at the base before planting. This will help feed the bulbs and will also retain water to ensure a more regular supply. If you have bought quite a few, don’t plant them all at once. Plant fifteen corms every couple of weeks from early May to July to give a succession of flowers through the summer and autumn.
Plant five corms in a 15cm (6in) pot at 20cm (8in) deep, so a bit more closely packed than recommended above. Put them somewhere bright and cold, but frost-free, and water. Wait for them to shoot and plant them out in the garden from May onwards, by which time you’ll have well established plants. They will need staking. To avoid piercing the corms, canes are safest poked in before you plant the bulbs.
On well-drained, poorer soil, extra watering will be required. Apply a high potash feed, like comfrey pellets or tomato fertiliser every two weeks as soon as the flower spikes are 15cm (6in) high and until at least three weeks after flowering. This is essential on poor soils as flowering can diminish in successive seasons. Gladioli will flower three months after planting.
It's always said you need to lift your gladioli - that, like dahlias, they'll be frosted if left in the ground. It's my fourth year of growing them at Perch Hill and I've never lifted them. I mulch them deeply with 6-7cm (2.5in) of mushroom compost to give them an insulating duvet over their heads in late autumn. You should be safe with this in the south of England and the western fringes of the British Isles, but in colder counties, grow them in a sheltered spot and lift them for the winter when the leaves turn yellow-brown. Lift them and snap the corms from the stems. Dust with sulphur and dry them out for a couple of weeks. Then snap the new corms from the old, discarding the old. The new must be kept dry and cold (but frost-free) until they are replanted.
You can dig and divide the clumps every few years to select the best corms for replanting. Without this, the new cormlets forming will invade the space of the original corm and the nutrients will have to be shared. The danger of this is the creation of lots of foliage and no flower spikes.
Remove the bottom leaves, I prefer to leave the spike tip as this is part of the plants appeal but removing it will encourage more flowers below.