Val Bourne says it’s crucial to delay until night-time temperatures improve before you start sowing seeds

It’s so easy to buy a packet of vegetable seeds and, having noted that the packet says sow in February or early March, to take it seriously and do so. However, the garden has its own calendar and at this time of the year you have to wait for signs of spring.

Do not be seduced into sowing when the temperature climbs towards a sitting-room perfect 20C (70F) on crystal clear days, because the likelihood is that it will be plunging towards zero at night.

Wait for warmer nights, even if it means cooler days, before you expose your seeds to the soil for extremes of any kind are bad for most plants.

I have been trying to teach the Best Beloved this for years, because he plunges in too quickly and last year not a carrot came up from the seven packets he sowed.

I’ve learned to be wise and bide my time, having watched my ex-neighbour George in Hook Norton. His timing was spot-on and he inevitably sowed and planted later than I did, with much better results. George made sure the weeds and grass were growing and the birds singing, and he waited for dry soil too before he lifted a finger.

Mid-March, in an ideal year, is the perfect time to sow parsnips if spring is in the air.

These umbellifers, members of the cow parsley family, need temperatures of 12C and even then they take a full 30 days. Opt for F1 varieties and I am a fan of ‘Gladiator’, an AGM (Award of Garden Merit) variety that’s widely available.

Always sow parsnips in calm weather, because their papery light seeds will scatter on a windy day.

I believe in making a four-inch drill and watering well before sowing. Then I scatter seeds, trying to space them well, along the wide drill and then cover the ground with wire netting. Charles Dowding, a Somerset-based vegetable expert and author, sows his parsnips close to Cheltenham Gold Cup week — which is upon us now.

If the weather is good I will sow some carrots too. The early varieties (such as ‘Amsterdam Forcing’ and ‘Early Nantes) mature quickly so I should be pulling carrots by June. They also get sown into four-inch drills that have been well watered, because I don’t thin my root crops out.

In a couple of weeks I will also sow ‘Purple Haze’, a purple-skinned sweet carrot that my family love to eat. Beetroot can also be sown then and the old variety ‘Boltardy’ is still popular because it copes with dry, cold weather. The Blackthorn winter, a series of cold days that prompt blackthorn to flower, can make spinach and beetroot bolt and run to seed.

My chosen beetroot variety is an F1 called ‘Alto’ and this produces sausage-shaped beetroot that mature faster than the rounder varieties.

It stands well and last year’s crop stayed in the ground and was finished up at Christmas.

My root crops are sown in 8ft x 4ft beds because this allows you to sow and harvest without walking on the soil. A short builders’ plank is an ideal part of any gardener’s kit, because preserving soil structure is key.