6 Kilograms of Maincrop from a Charlotte Potato Row Grown in a Dalefoot Bag

Three seed tubers went into one 40-litre Dalefoot wool compost bag in the third week of March. The variety was Charlotte, a second early often pushed toward maincrop weight if left in longer. Lifting happened in mid-July, roughly 16 weeks after planting. The bag held 6.1 kg across the three plants, which works out to just over 2 kg per tuber. For comparison, a metre of open-ground Charlotte row at standard spacing tends to return 4 to 5 kg under average conditions, so the container came out ahead on a like-for-like footprint.

The compost is worth naming because it changes the watering maths. Dalefoot’s peat-free wool-and-bracken mix holds moisture longer than a standard multipurpose, and the wool releases nitrogen slowly as it breaks down. No additional feed went in beyond the two liquid tomato-food doses applied once flowering started. That is a leaner regime than most container potato guides recommend, and the yield did not appear to suffer for it.

The chitting weeks that set the calendar

Chitting began in early February, six weeks before planting. The tubers sat in a cool, frost-free porch at around 8 to 10 degrees C, laid in a used egg tray with the rose end (the end with the most eyes) facing up. Light matters more than warmth here. Kept too warm and dark, tubers throw long white etiolated shoots that snap off during handling; kept cool and bright, they produce short green-purple sprouts of 1 to 2 cm that survive transplanting.

By planting time each tuber carried three or four stubby sprouts. A common instruction is to rub off all but two or three of the strongest, on the logic that fewer stems means larger individual potatoes. That rub-off step was skipped here. All viable sprouts were left on, which favours a higher count of medium tubers over a handful of bakers, and for a salad variety like Charlotte the medium grade is the point. The 6.1 kg broke down to 41 tubers, none above 90 g, most in the 40 to 70 g band that sells as a premium salad potato.

Earthing up in a bag is simpler than in a trench. The bag was rolled down to half height at planting, tubers set on 12 cm of compost, then topped with a further 8 cm. As the haulm grew, the bag was unrolled and more compost added twice, keeping developing tubers covered against greening. The final fill reached about 35 cm depth.

Why the carrots stayed under mesh the whole time

Carrot root fly does not fly high. The adult female, Psila rosae, cruises low over the soil surface searching for the scent of carrot foliage, and most of the population operates within about 45 cm of ground level. A physical barrier that height, or an enclosure over the crop, defeats a large share of egg-laying attempts.

The carrots on the same bench sat under Enviromesh from sowing in April. Enviromesh has a mesh aperture around 1.35 mm, fine enough to exclude the root fly while passing light and rain. The netting was laid over hoops and buried at the edges with soil, leaving no gap at the base where a female could crawl under. It stayed on until lifting. No thinning was done in the open air; the mesh was lifted briefly, thinnings pulled, and it was replaced within minutes, because the bruised foliage from thinning is exactly the scent plume that draws the fly.

Crop rotation on the onion bed

The onion sets went into a bed that had carried legumes the previous season, following a three-year rotation of alliums, then roots, then legumes and brassicas. The point of moving onions off the same ground is white rot, Sclerotium cepivorum, whose resting sclerotia survive in soil for 15 years or more and build up under continuous allium cropping. Rotation does not eliminate an established infection, but on clean ground it delays the point at which the fungus reaches damaging density.

The drip line that made the watering repeatable

Hand-watering a container potato bag is unreliable because the surface wets while the core stays dry, or the reverse. A single 4 litre-per-hour dripper was pushed into the compost about 8 cm from a stem and run off the same low-pressure line feeding the raised beds. The line ran on a battery timer set to 12 minutes at 6 am, delivering roughly 0.8 litres to the bag per cycle, adjusted to two cycles daily once July temperatures climbed past 25 degrees C.

The raised beds on the same circuit used 4 litre-per-hour drippers spaced at 30 cm along a 13 mm supply tube. Pressure-compensating drippers matter on any run longer than about 4 metres or with any height change, because otherwise the emitters nearest the tap deliver more than those at the far end. On a level 5 metre bed the difference between compensated and non-compensated emitters showed up as visibly larger lettuces at the near end within a fortnight.

The wool compost changed the schedule. Because the Dalefoot mix retained water so well, the bag was checked by pushing a finger to the second knuckle before trusting the timer; on cool overcast stretches the 6 am cycle was skipped entirely to avoid waterlogging, which in potatoes invites the soft rots that turn a stored tuber to liquid. Waterlogging also drives up the risk of common scab being masked while a worse rot develops underneath. The finger test, unglamorous as it is, overrode the timer perhaps one week in four.

Cucumbers trained up the same greenhouse the potatoes started in

The potato bag spent its first three weeks on the greenhouse bench before moving outside once frost risk passed in late April. That freed the bench for two cucumber plants of the variety Carmen, an all-female F1 that sets fruit without pollination and so does not turn bitter from accidental fertilisation.

Training was vertical up a single string clipped to a wire at 2 metres. The growing tip was wound clockwise around the string every few days, and side shoots were pinched to two leaves beyond the first fruit. Tendrils were removed on sight, because a tendril that grabs the main stem or a leaf wastes the plant’s energy and creates a tangle that hides developing cucumbers. The lower 50 cm of stem was kept clear of fruit and side shoots to keep air moving and reduce the botrytis that starts on damp lower leaves.

Feeding ran heavier than the potatoes: a high-potassium tomato feed twice weekly once the first fruit set, because a cucumber plant carrying six fruit at once is a genuine drain. Water went in at the base only. Wet foliage in a closed greenhouse at 28 degrees C is how powdery mildew establishes, and Carmen, while vigorous, is not immune. Two plants delivered a cucumber every second or third day from late June through September, which for a household of four was slightly more than could be eaten.

The contrast between the two crops on that bench is the useful part. The potatoes wanted a lean feed and cautious water and rewarded neglect; the cucumbers wanted heavy feed and constant attention and punished any lapse with bitterness or mildew.

What the single-bag figure does not tell you

6.1 kg from one bag is a strong return, but it came from one season, one compost, and one weather pattern. The open question is durability: Dalefoot wool compost is sold as reusable for a second year with topping up, and whether a bag that gave 6.1 kg of Charlotte will give anything close after the wool nitrogen has largely gone, without a full refresh, is the number worth chasing next.