Earthing-up Potatoes and Compost Sieving

"It is a mistake to think you can solve any major problems just with potatoes" - Douglas Adams 

"What I say is that, if a person really likes potatoes, they must be a pretty decent sort of person" - A. A. Milne (amended)

This year's seed potatoes were planted outside on 31st March after a six-week chitting period. At, or around, the 23rd of April the first green shoots appeared above ground.

Photo 1: First Foliage (23/4/23)

Since frost was predicted over the next few days, these early shoots were covered with a layer of compost. Early on the 25th April, we did indeed experience subzero temperatures, between -1 ℃ and 0 ℃, so frost damage would have been minimal anyway.

By 11th May, there was plenty of visible growth (Photo 2) and it was time to earth-up the soil around the potato shoots. The benefits of earthing-up are (i) frost protection, (ii) increased yield (more space for tubers to develop), and (iii) reduced light exposure to the near-surface tubers to prevent them from turning green. Typically, this would be done by drawing soil from the valleys to the ridges using a hoe or rake.

Photo 2: More green shoots (11th May)

However, because I grow my potato rows close together in a raised bed, I prefer to build up the ridges using homemade garden compost (Photo 3) which has the added benefits of nutrient feeding and mulching:

Photo 3: Ridge building with compost

More compost will be added to the ridges during the growing season. A similar process is used for the two potato grow bags, except the addition of coir*/compost is more often and more regular - every time new shoots appear above the surface, they are covered up with 1:1 coir*/compost until the bag is full (Photo 4).

*recovered from last year's Quadgrows and Salad/Veg Planters.

Photo 4: Full potato grow bags

This sudden burst of activity was brought on by the need to clear one of my four compost maturation bins (Photo 5). My composting process comprises an initial 'hot composting' period, to kill pathogens and weeds, followed by a slower maturation period of 6 months or more to allow the worms and other micro-organisms to do their 'business' - literally, in the case of the worms!

Photo 5: Compost Maturation Bins

I had compost from Stage 1 (hot composting) ready to move onto Stage 2 (maturation) so that I could make space in the hot composters for the recent influx of garden waste. It was the turn of MATBIN3 (third from the left or second from the right, Photo 5) to be emptied after approximately one year's maturation.

Photo 6: MATBIN3 part-emptied

The finished compost in MATBIN3 (Photo 6) was both sticky (i.e. lots of woody bits) and sticky (i.e. lots of moist black humus). This material can be used as seen to add nutrients, carbon and beneficial micro-organisms to the soil - either dug in or as a mulch. However, I also needed some sieved compost for potting-on new plants, filling up the potato grow bags, top-dressing existing pots, and surface-dressing ornamental beds (where the sticks are a little unsightly). So I decided on a sieve-lite approach whereby I filtered out about 40% of the rich humus ...

Photo 7: Sieved humus-rich compost

 ... and used the remainder ...

Photo 8: Residue after sieve-lite operation

... to earth-up the potatoes. [Note: a typical compost sieving procedure would produce between 70-90% of sieved humus-rich material with the residue returned to a maturation bin for additional processing].

In a month or so, I'll be back to earth-up the potatoes again with more compost. Time for a cup of tea, now.