Brussels sprouts can be a little tricky to grow. Problems most likely to be encountered include;
Wilting young plants: Plants may wilt after planting due to lack of water. Adequate water at planting and subsequently is required. A ‘starter fertiliser’ can help (high phosphorus liquid fertiliser used at half strength). If plants are readily pulled up (i.e. not firmly anchored) and there are few roots and damaged lower stems the likely cause is cabbage root fly.
Lack of growth: Brussels sprouts need very fertile soil indeed to perform well. As much as 300g per sq m (10oz per sq yd) of Growmore applied one third before and two thirds after planting are required for best results. Equivalent quantities of other fertilisers can be used instead. Adding plenty (two bucketfuls per sq m) of organic matter can replace half the fertiliser. Brussels sprouts are much more tolerant of drought than cauliflowers but require moist soil in summer if they are to grow well. Plants should also be allowed at least 60cm (2ft) between plants and rows, and allowing 90cm (3ft) between rows eases access for gathering sprouts. Brussels sprouts require watering every 14 days in dry spells.
Few sprouts: The number of sprouts is dependant on the number of leaves. For plenty of leaves early sowing (late winter or early spring) is essential and careful planting into very fertile soil and subsequent careful watering.
Loose-leaved sprouts: Sprouts, like all brassicas, require to be firmly planted. A leaf should tear if tugged before the plant can be dislodged form the soil. However, loose planting is not a direct cause of fluffy sprouts. The usual cause is poor soil, lack of growth and especially the use of non-hybrid cultivars. Only hybrid cultivars can be relied on to produce firm sprouts. Excessive nitrogen fertiliser is not implicated in loose sprout formation.
Tasteless sprouts: Sprouts tend to be bland until mid-autumn when with the advent of cold weather they become sweeter and more palatable. Certain early cultivars have been bred to be tasty as early as late summer, but even these cannot match the sweetness of later cultivars.
Bitter sprouts: Most modern sprout cultivars are free of the bitterness once found in sprouts. Those with the RHS AGM have been tasted by RHS experts and found to be free of excessive bitterness.
Tunnels in the sprouts: Cabbage root fly also occasionally tunnel the sprouts as well as affecting roots. There is no remedy but to grow crops under insect-proof mesh in gardens where this damage recurs.
Disfigured sprouts and leaves: In wet winters and regions leaf spot and ringspot fungal diseases cause concentric circular marks to form on leaves and sprouts. Some cultivars are less affected and are listed in seed catalogues. Yield is not seriously affected as sprouts marked in this way can be peeled.
Plants fall over: In exposed gardens plants can fall over (lodge) in high winds. To avoid the chore of staking plants choose shorter cultivars (listed in seed catalogues) and draw soil 15cm (6ins) up stalks in late summer using a draw hoe. Crowded plants are more vulnerable to lodging.