General
Spinach, native to Central Asia and Persia, was once called “Prince of Vegetables” by the Arabs. It was introduced into France at the time of the Crusades. During the Renaissance, spinach was grown in royal gardens. It is said that Louis XIV reserved a privileged place for it at his table. It is said to have some therapeutic properties due to its high iron content and high vitamin A content.
Spinach belongs to the Chenopodiaceae family, along with beetroot and Swiss chard. It is an annual plant that is grown as such or more often as a biennial. The green, smooth or embossed leaves are arranged in a rosette shape. The flowers grow on a 60 to 80 cm high flower spike. In general, the plants are dioecious, the female and male flowers are on different legs. Cross-pollination is the rule, and pollen transfer is ensured by anemophily. There are about 100 seeds per gram. Their germination can be up to 5 or 7 years. Note that there are two types of seeds: smooth and prickly. The latter would make the plants less sensitive to seed emergence.
Classification and varieties
Spinach is normally a long-day plant, i.e. it flowers when the days get longer. (With the exception of some varieties, spinach is very sensitive to the photoperiod). It is not uncommon for sowings in April and May to start sowing too early. The normal spinach crop is therefore stopped in autumn and early spring. However, thanks to research, the gardener now has varieties that are adapted to the short days of autumn (normal cultivation) and the long days of summer. Short-day varieties, whose leaves are harvested from autumn to spring, include Giant Winter Spinach, Virkade, Viking and many F1 hybrids (Samos F1, Andros F1, …). Only certain varieties allow a satisfactory harvest in summer: Estivato, Caballero F1, Spencer, …
Cultural requirements
Spinach does not like a climate that is too warm and is therefore well adapted to our regions. In practice, it does better in cool weather and is more resistant to frost than many other vegetables. The cold resistance depends on the variety, temperatures of around -5° C do not have an unfavourable effect on this crop (-7° C for the Winter Giant). It fears drought which makes it go to seed. It is therefore an ideal vegetable to grow in your greenhouse. At soil level, spinach fears both drought and persistent humidity. Therefore, choose a lighter soil for winter crops and a heavier soil for summer crops. This plant fears acidic soils, the pH must be between 6.5 and 7.5 depending on the soil type.
From the point of view of fertilisation, spinach is a demanding plant. A supply of fertiliser of 800 to 1000 kg per hectare is sufficient. This stock should be built up well before sowing to prevent root rot. For chemical fertilizers, the basic formula for foliates can be used: 4 kg of ammonium sulphate, 6 kg of superphosphate and 4 kg of potassium sulphate per hectare. Later application of nitrates may be necessary if vegetation is difficult to start.
Culture
Two types of cultivation can be distinguished: summer cultivation and autumn cultivation. Spinach is often used as an intermediate crop, that is, before or after another so-called main crop. Spinach can be grown after early potatoes or before leeks.
In the case of autumn, sowing is successively from August to early October. The first two harvests take place in September and October, while sowing in September allows for a spring harvest. Winter protection using a frame makes it possible to harvest in winter. Germination is often erratic, watering is beneficial for it. We sow in rows with a spacing of 15 to 30 cm. The soil is then plumed and it is not useless to protect your seedlings from unwanted birds. For the May and June harvests, sow in March, early April. Usually some light hoeing is done. The ammonium nitrate is buried during this period.
Harvest
Harvesting begins when the plant has 6-7 leaves and continues until the flowering peak. Harvest leaf by leaf, starting with the most developed leaves. Harvesting should be done in dry weather to prevent the leaves from becoming brittle. If you have a large harvest, freezing your spinach will be very satisfying.
Crop protection
Yellowish spots on the canopy are due to powdery mildew. This disease occurs in soils that are too wet or in seedlings that are too dense. Spray with captan or maneb products. Finally, there are more and more varieties that are resistant to this fungal disease. Summer crops are often attacked by aphids that deform the canopy. In addition, these pests often carry incurable viral diseases that damage the leaves.