A remarkable plant that offers much more than fruit: the luffa is the sponge that grows in the garden.
About the variety. Indeterminate in growth and climbing in habit, it produces cylindrical fruits that reach medium-large size. Flowering is photosensitive — it only begins when daylight drops to 12 hours, in September. Left to dry on the plant, the fibrous flesh transforms into a long-lasting natural sponge. It prefers rich soils and frequent watering.
Itinerário técnico
Como cultivar luffa?
Um guia de cultivo passo a passo, da sementeira à colheita.
pH ideal 6.0 to 7.0Temperatura ideal 22 to 32 °CCompasso 50 cm in the row, 100 cm between rows
Sementeira
Sow in individual pots four to six weeks before planting out, two centimetres deep, at 25 °C to 30 °C. Soak the seed for twenty four hours in warm water, because the coat is hard and germination slow. It has one of the longest cycles in the garden and without an early indoor sowing it will not produce mature sponges outside the south of the Peninsula. The first flowers are all male and set no fruit; if later the small fruits shrivel, pollination is failing: hand pollinate early in the morning with a brush. It climbs vigorously and needs a solid support, which keeps the sponges straight and clean.
Solo
It wants deep, loose soil, very rich in organic matter and free draining, with a pH between 6.0 and 7.0. The classic approach is to open a wide hole, fill it with mature compost and plant on that spot, which gives the plant the reserve it needs. Rotate on a four year cycle with crops from other families.
Clima
It needs strong steady heat, between 22 °C and 32 °C, full sun and four to five months without cold. Outside southern Iberia it is only worth growing under glass. This is a long cycle variety. Sow indoors in March and plant out only with the soil above 18 °C; a greenhouse or a south facing wall makes up the weeks that the Atlantic coast and northern Europe lack. In the dry heat of inland Iberia water well and give some shade in weeks above 35 °C, when the plant stops setting fruit. At the end of September, a fleece cover on cold nights extends the season enough to finish drying the last sponges.
Fertilização
Work two to three kilos of well rotted compost into each square metre before planting and add a handful of wood ash to top up potassium. Once growth is away, feed with a liquid organic fertiliser every two or three weeks, moving from a balanced formula to a higher potassium one as cropping begins. Avoid excess nitrogen, which gives lush leaves, a poor crop and a lot of aphids.
Rega
Water generously and regularly through the whole growth phase, because the plant makes a great deal of growth in a short time. Reduce watering once the fruits destined to become sponges begin to yellow and dry on the plant.
Controlo de Infestantes
The critical period is the first month, before the foliage covers the ground. Hand weed in that phase and, once the vines start to run, stop disturbing the soil: from then on the plant smothers weeds itself. A straw mulch under the foliage keeps the fruit clean and dry and greatly reduces losses to rot where fruit touches the soil.
Controlo de Pragas
The main pests are aphids, red spider mite, thrips and whitefly, and on young plants slugs and snails, which can cut down a newly emerged seedling in one night. Protect the seedlings with a cut bottle or an ash barrier for the first weeks. Against aphids and whitefly use potassium soap in the late afternoon; against red spider mite, which appears in dry heat, wet the leaves in the morning and use neem oil.
Doenças
Powdery mildew is practically unavoidable and shows as white dust on the upper leaf surface, above all from midsummer on. It is checked with potassium bicarbonate or sulphur applied at the first signs, together with removal of old leaves and good airflow. Cucurbit downy mildew gives angular yellow patches bounded by the veins and thrives in coastal humidity. Anthracnose and collar rot appear in waterlogged soil. Use a four year rotation and clear all crop debris at the end of the season, because that is where the fungi overwinter.
Colheita
For eating, pick the fruit under fifteen centimetres, still tender and free of fibre. For sponge, leave it on the plant until it is brown, light and rattling; then peel it, shake out the seed, wash it well and dry it in the sun. Picking too early for sponge gives a soft fibre that falls apart. Allow about 120 to 130 days from transplanting to the first harvest of this variety. The reference colour is green (brown when dry), and that is what tells you it is ready.
