Digging, Liming and Edging

Digging over the potato beds

I have written earlier about how much I hate digging. But some digging is necessary. You can’t get your potatoes out of the ground without digging. (This doesn’t actually feel like digging, it feels like harvesting, which is much more fun.)

I have found over the last few years that I miss too many spuds first time through. As a result, potatoes grow in the middle of the next crop the following year, as weeds.  Both annoying, and a waste. So nowadays I dig over the potato beds a second time looking for strays. This is quite easy to do, as the soil is already loose.

I put a couple of wheelbarrows at one end of the bed, dig out a trench a spade wide and one spit deep, putting the soil into the wheelbarrows, then move them to the other end of the bed. (That is the hardest bit.) Then I turn the next spade-widths of soil into the first trench, salvaging any stray spuds that surface, and so on until the whole bed has been turned, finishing by putting the soil from the wheelbarrows into the final trench.

Double-digging

This is optional, and admittedly does feel more like work and less like fun. And I only ever intend to do this once. But while digging over the potato beds, I loosen the soil at the bottom of each trench with a fork.  This is called “double-digging” and is a way of increasing the depth of soil available to plants.

Some books say that you should put compost or manure at the bottom of the trench before double digging. I am not sure about this. The crops that follow potatoes in my plan are alliums (the onion family) and legumes (the pea and bean family).  These are all fairly shallow-rooting crops and need nutrients nearer the surface rather than deep down. And there should already be sufficient nutrients in the soil after the previous year's manuring for the spuds.

After double-digging, roots can more easily penetrate deeply in search of nutrients and water. (I knowI have just said that the plants that will immediately follow have their roots near the surface. But other crops, especially root crops like carrots, parsnips and chicory, will benefit greatly from the increased depth available.)

I am also slowly increasing the depth of soil from above too, by regularly adding compost and manure to the beds. By increasing the soil available vertically in this way, it is possible to grow plants closer together, thereby increasing yields.

Of my 20 beds, I have 5 beds down to potatoes each year, and if I work on each of these beds I will have double-dug the whole thing in 4 years. Afterwards, by scrupulously avoiding treading on the soil, this increased depth should continue to be available to plant roots every year without any further double-digging.

Liming

Repeated heavy cropping and application of manure increases the acidity of soil. Most vegetables don’t like acid soil. The main exception is potatoes. To grow good spuds, the soil needs to be fairly acid. At the other end of the scale, the brassica family hate acid soil. To grow good cabbages, cauliflowers, etc the soil needs to be quite alkali.  Other vegetables lie somewhere between these 2 extremes, although most are closer to the brassicas on the acidity-alkalinity scale than potatoes.

To reduce the acidity of soil, it is necessary to add lime. Some allotmenteers don’t bother. Those that do lime tend to do this before planting out their brassicas. One advantage of doing it then is that lime does help combat the dreaded club-root disease.

I don’t have club-root on my allotment and prefer to lime after the potatoes. So once I have dug over the potato bed, recovering any stray spuds and loosening the soil, I rake it level and then apply lime.  Some books tell you to use a soil test kit to assess exactly how much lime to add, but I don’t bother. I just add the amount recommended on the packet as a general soil treatment for vegetables.

Edging

Now that my outgoing potato bed has been dug and limed, the soil is loose and ready for the next crop. It is at this stage that I find it easiest to edge the beds with scavenged planks or bought decking boards. I simply slide the boards into the loose soil and then bash in retaining posts (which can very easily penetrate more than 12 inches into the double-dug soil), securing them with screws.

Last year we edged the central path which runs the length of the allotment. This year I am edging 5 ex-potato beds, and over the next 3 years I will be edging the remaining beds after lifting potatoes, until the entire allotment has edged beds.