This section is from the book "The Gardener V3", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
The earliest and most profitable crop of these will be obtained from an east border, the soil of which should be rich and firm. On the first favourable opportunity in March seed should be sown of the Early Munich, and more of the same variety, and also of a good selection of Snowball towards the end of March or early in April. It is a great mistake to crowd Turnips; and to induce early bulbing, the rows should at least be 15 inches apart, and the seedlings at the second thinning be left about 9 inches apart. An occasional dusting with soot and lime is necessary to preserve the young foliage from fleas.
These are still more important, in the cook's estimation at all events, and are often grown with difficulty during the hot summer months. For these reasons it is advisable to grow a crop on a north border. As before stated, we make our earliest sowings on an east border, commencing on the north border about the second week in June, giving the preference to a good strain of Snowball. Turnips often fail owing to insufficient pains being taken with the ground, and later on with the young plants. A tolerably rich firmly trod soil should be given them, and they should be encouraged to grow quickly, and never be crowded. If the ground be dry at sowing-time, after drawing the drills, water them well over-night or a few hours previous to sowing. This will be found more effective than watering after the seed is sown, and the ground levelled, as the enclosed moisture does not so quickly evaporate. Of course these remarks are equally applicable to the sowing of other kinds of seeds. At this time of year it is always advisable to sow small patches of Turnips at fortnightly intervals in preference to one large one.
Sow seed thinly, dust over the seedlings with soot and lime on the first appearance of fleas, and thin out early.