Successional Sowing Outdoors
With the soil warm enough, a huge range of vegetables can be sown directly into your prepared beds. Start sowing the following on a successional basis – i.e. small quantities every 2 to 4 weeks to give a steady supply and avoid gluts.
- Summer cauliflower
- Summer cabbage
- Summer sprouting broccoli
- Winter brussels sprout
- Spring onion
- Pea and mange tout
- Broad bean
- Kohl rabi
- Various herbs
Maincrop Vegetables Outdoors
With these you sow/plant all that you’ll need for the year in one go. Again, sow/plant only when the soil is ready.
- Onion sets (as soon as possible)
- Onion seed (as soon as possible)
- Leek (as soon as possible)
- Salsify and scorzonera
- Swiss chard
- Autumn cauliflower
- Autumn/Winter cabbage
- Red cabbage
- Winter/Spring sprouting broccoli
- Jerusalem artichoke
- Potato (See below for details)
Note that swede, belgian chicory and pak choi are not sown until next month. This is because they have a tendency to bolt (run to seed) if sown too early.
When the soil is ready for seed sowing it is also ready for potato planting, both early and maincrop varieties. Plant in rows 2ft apart, 1st early varieties spaced 12” apart, 2nd early and maincrop varieties spaced 18” apart. Planting depth is around 6”. Potatoes like a moisture retentive soil, so plant in a bed prepared with a good amount of organic matter.
To Be Started Off Indoors
Florence fennel, celeriac and celery, although hardy plants, need a warmer soil to germinate. Hence, they are sown indoors, at a temperature of around 10-15ºC, and planted out next month.
The following need to be sown indoors because they are half-hardy and so cannot survive frost. They are planted out next month, after the last anticipated frost.
- Basil 
- Squash and pumpkin 
- Outdoor tomato, cucumber and aubergine 
- Sweetcorn (choosing a variety suitable for a northern climate) 
- French beans
- Runner beans
 Basil: two new varieties I want to try this year are ‘British’, developed specially for our climate, and ‘Summer Surprise’, a purple variety with good vigour and response to cropping.
 If you’re thinking of trying butternut squash, try ‘Harrier’ or ‘Hunter’. Both these varieties do well in our climate.
 Cucumbers: there are a number of new, often small sized, varieties that are a great improvement on the old outdoor varieties. Eg ‘Rocky F1’ ‘Beth Alpha’ and ‘La Diva’ (all smooth with good taste and texture).
 Personally, i’ve found ‘Swift F1’ and ‘Sundance F1’ to do well in a typical Edinburh summer. If you have the greenhouse space then you could go for one of the supersweet varieties such as ‘Lark F1’ and ‘Prelude F1’
Hardy Annuals Sown Directly
Once the soil becomes warm enough (see above), sow hardy annual flower seeds outdoors. In most cases, a fairly impoverished soil will give best results; indeed, too much organic matter or fertilizer is often counter-productive. Weed the area in which the seeds are to be sown and rake the soil to produce a fine tilth. Then hold off sowing for a couple of weeks and allow all the weed seeds to germinate. Removing these, with minimal soil disturbance, will give you a ‘sterile’ bed on which to sow your flowers.
Some suggestions for easy-to-grow hardy annuals:
- night-scented stock
- Californian poppy
- corn marigold
Half-Hardy Annuals Sown Indoors
There is still time to sow half-hardy annuals (marigold, brachyscome, bidens, morning glory, antirrhinum, lobelia, impatiens, cosmos and petunias, for example). By April, however, you’re leaving it a little late so get these sown – in a heated greenhouse or a cool conservatory, or a bright windowsill in a cool room – as soon as possible And bear in mind however that the more common of these plants, such as lobelia, petunia and impatiens, can be bought in the shops or mail-order at very reasonable prices in the form of plug-plants.
Many perennials grown from seed can still be sown. Treat these as you would half-hardy annuals until they are planted out.