Some years ago I went on a course with Jim Cronin over at his smallholding in Co Clare, and he outlined this method, which creates very deep beds and gives you an abundant crop.
Cultivate the soil in the bed in the tunnel where you are going to sow spuds and make it loose. Take the soil from the bed (down to the subsoil) and put it out on to the path. Put your seed potatoes on to the subsoil at 10 inch spacing. On top of each potato put a little bit of soil. Put 15 inches of farmyard manure on top of the spuds. The little bit of soil stops the manure from burning the seed potatoes. The manure can be fresh or composted. Then put the soil from the path back on top of the manure. It is the depth of manure and soil on top of the seed that encourages a long stalk and therefore lots and lots of lovely spuds.
Put some fleece on top to protect from cold weather. Take fleece off when potato plants appear but put back on at nighttime where frost is a risk. Hoe occasionally to prevent weeds from taking hold, until the plants produce a canopy of leaves, which will prevent weeds. Do not water until some of the plants start to flower – probably April. There is enough moisture in the air in the tunnel in Feb and March and if you water too early you will get tall, leafy plants but few spuds. Start to look for spuds from early May. Cut stems down to 2 inches in July (if you still have any spuds left by then), which will allow you to leave them in the ground for longer.
The Basics – Jobs for the Month Ahead
If you have not already done so order/buy your seeds, spuds and onion sets. “Chit” or sprout seed potatoes – put them in a container (e.g. used egg carton or empty seed tray) and leave them in a bright warm place. Check the pH of your soil – you can buy a soil pH testing kit in any garden centre. Lime your soil now if required (to reduce acidity in very acid soils), particularly important in your brassica bed.
Later this month we can, finally, sow some seeds. On a sunny windowsill indoors, in a heated greenhouse or on a heating mat: sow celery, globe artichokes, celeriac, leeks, onions, lettuce, tomatoes, peas, aubergines, peppers/chilli-peppers. For polytunnel or greenhouse: beetroot, carrots, leeks, lettuce, radish. Outside: Weather permitting you can try planting out broadbeans and early pea varieties.
You could still be harvesting carrots, leeks, celeriac, Winter cabbage and cauliflowers, Brussels sprouts, spinach and kale.