Mould and Rot in the Root Cellar

Alberta Agriculture publishes an instruction for a cellar with rot in it, and it is to take the affected produce out as soon as you see symptoms. That sentence is written about carrots in Home Vegetable Storage (Agdex 732-15), and it is the clearest published answer this site can point a Canadian root-cellar keeper at.

What they do not publish is whether a mouldy or rotted vegetable may be eaten. Nor does any other Canadian authority we can reach. There is one exception, it is about potatoes, and it is further down this page.

What Alberta describes, crop by crop

These are their descriptions, not ours. Matching what you are looking at to one of them is the point — several of these look alike and start in different places.

Carrots

	What Alberta writes
Cottony soft rot	”a white cottony-looking mass on the surface of the carrot. Often black raisin-like structures are seen in the white mass, and carrots become soft and watery.” Caused by a fungus “that can grow quickly even at low storage temperatures” and “found in garden soil and … present on the carrots when they are brought in from the garden.”
Grey mould	”Infected carrots at first appear light brown and water soaked, but later become spongy and leathery. The surface of the carrot is covered with a grey-brown mass of fungus.”
Soft rot	”Soft rot is caused by bacteria. Infected carrots become soft, watery, and are foul-smelling.”

Their control measures: avoid bruising and wounding during harvest; wash and disinfect storages and holding containers before use; avoid storing wet carrots; remove infected carrots from the storage as soon as symptoms are seen; avoid planting in the same spot two years in succession.

Cabbage

Grey mould “spreads rapidly through stored cabbage causing a brown soft rot. Usually a grey-brown, felt-like mass of fungus appears on affected parts.” It enters through bruises and wounds, and Alberta notes that the rot is restricted to the outer leaves. Dark leaf spot gives leaves “a dark brown or black discolouration and a dry leathery texture.” Soft rot is bacterial: “Cabbage heads become soft and mushy.”

Their control measures: do not store cabbages that have been wounded or bruised; trim diseased outer leaves before storing; clean and disinfect the storage before storing cabbage; remove infected plants when symptoms are observed.

Potatoes

Bacterial soft rot gives “a pock-marked appearance” — blisters collapse into sunken areas, and “when the blisters are broken and the tuber is squeezed, rotten tissue squirts out. The ooze is at first cream coloured but later becomes dark and foul-smelling.” Alberta adds that it “can occur on either frost-damaged or wet potatoes that are put into storage.”

Dry rot is the one that hides: “may first become evident as a clearly visible shrinking and darkening of part of the tuber, or it may progress toward the centre of the tuber, and serious decay may start before external symptoms become visible. A cavity covered with a white cottony mass may form inside the potato.”

Blackheart is not a disease at all. “A dark black spot is present in the center of tubers when they are cut open. This disorder is caused by lack of oxygen during storage.” If you are finding it, the pile needs air rather than treatment.

Their control measures: avoid damaging or bruising at harvest; do not dig when the soil is wet; dry wet potatoes before storing; store in the dark; cure before storage at 12 to 16 °C for seven to 10 days to promote wound healing; provide adequate ventilation.

Onions

Neck rot is invisible when you make the decision. Alberta: “Infected bulbs look sound and healthy going into storage but eight to 10 weeks later become brown and discoloured inside.” Soft rot is bacterial — “soft and have a water-soaked, yellow-grey appearance. When squeezed, a foul-smelling liquid is emitted” — and enters through wounds in the bulb and neck, including wounds made by the onion maggot.

Their control measures: grow early-maturing, tight-necked varieties and seed as early as possible; do not fertilize with nitrogen after July; lift and cure when two-thirds of the tops are down; control onion maggots; avoid injury during cultivation, harvesting and storage; cure onions at 26 to 30 °C for seven to 10 days.

Winter squash and pumpkin

Soft rot: “The rind at first appears water-soaked but soon breaks down into a watery, foul-smelling mass.” Cottony soft rot: “The rind develops water-soaked spots but is later covered by a cottony, white, fungal mass.” Frost damage looks like the start of both and is not an infection: “Frost damage causes the rind to develop water-soaked spots that become soft in storage.”

Their control measures: store mature winter squash only; avoid bruising or wounding the rind; pile no deeper than 60 cm. Alberta’s test for maturity is in their curing section — “the rind is hard and cannot be scored when pressed lightly with the edge of a fingernail.”

Damaged is not the same as diseased

Alberta draws this line itself, in two sentences a page apart, and it is the difference between eating something soon and not storing it at all.

“Damaged produce need not be discarded if it can be stored separately and consumed first.”

“Avoid storing produce that is diseased or has insect damage. This produce will not last long in storage, and disease will spread to healthy vegetables.”

Damaged means handled roughly — cut, bruised, skinned at harvest. Diseased means something is growing in it. The first is a sorting job at the door; the second does not go in, and if it is already in, the carrot instruction above applies to it.

The one thing Alberta does say about eating

It is about potatoes and it is about colour, not about rot:

“Potatoes not totally covered by soil in the garden or left in a room exposed to daylight or artificial room lights may develop a green colour. The potatoes should not be eaten if the tuber flesh is green as toxic chemicals are often found in association with green tubers.”

That is the whole of what Home Vegetable Storage publishes on whether a stored vegetable may be eaten. It does not extend to mould, to soft rot, or to a squash with a cottony patch on it, and we are not going to stretch it to cover them. Its own fix is storage in the dark, which Alberta says is “necessary to prevent greening of the tuber skin.”

What we are not going to tell you

Whether a mouldy or rotted vegetable is safe to eat. Alberta describes these diseases in detail and prescribes what to do with the produce in the cellar. They do not write a single sentence about the food on the plate, and nor does OMAFRA’s storage material or Québec’s food-safety pages, which cover canned and refrigerated food rather than a crate of carrots in a basement.

What you have instead is a published instruction — take it out as soon as you see it — and the reason behind it, which is that these organisms spread to the sound produce beside them. That is enough to act on. A verdict on eating it is not something we can source, so we are not inventing one.

Preventing the next batch

Alberta’s sanitation instruction is the only part of the booklet with a product in it:

“Storages should be cleaned as soon as the previous year’s vegetables have been removed. All plant material should be removed, and floors and walls swept clean. Shelving and bins should be scrubbed with soapy water and sanitized with a bleach and water solution (one part household bleach to 10 parts water). The storage should then be aired and repairs made.”

The rest of their prevention is about what goes in rather than what the room is like:

• Store mature produce free from cuts and bruises. Alberta: “Mature vegetables free from cuts and bruises store best.”
• Dry anything you washed. “Root crops can be washed, but they must be dried before being put into storage. If the product is wet, lay it out on a floor on newspaper or dry it with a fan.”
• Cure what needs curing. Potatoes, onions, pumpkin and winter squash, in the field or on arrival — “Curing allows the vegetable to heal wounds and set the skin.”
• Give the pile air. “Vegetable bins should be slatted and raised slightly off the floor so that air can move freely under and through the pile.” Blackheart in potatoes is the direct consequence of not doing this.
• Rotate the garden. Several of the fungi above come in from the soil, which is why Alberta’s carrot controls end with not planting in the same spot two years running.

If the produce is soft but not watery, and does not smell, this is probably not a disease at all — a cellar that is too dry does the same thing by drawing water out, and that is covered on root cellar too warm or too dry, which also carries Alberta’s full table of temperatures and humidities. For the room itself, see root cellaring in Canada. For mould inside a sealed jar rather than on a shelf, the answer is different and is published: see mould on home-canned food.

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