How to Grow Potatoes in Grow Bags, Step by Step

Pick the Bag, the Mix and the Spot

To grow potatoes in a grow bag, put 6 to 8 inches of potting mix in the bottom, set seed pieces about a foot apart, and cover them with 6 inches of mix. Add more mix as the stems lengthen until the bag is full, keep it moist, and tip the whole bag onto a tarp once the tops have yellowed and died. The rest of this guide fills in the sizes, timing and amounts.

University of New Hampshire Extension describes the ideal potato container as 2 to 3 feet tall with a capacity of 10 to 15 gallons, and Penn State Extension gives the same 10 to 15 gallon range. Going taller does not help. New Hampshire warns that the top of a very tall container dries out long before the bottom, which can stay soggy and rot the crop. The Royal Horticultural Society sets the floor at 12 inches wide and 12 inches deep.

Any container needs to be opaque and to drain. Fabric bags do both, and the handles make the harvest easier. The guide to grow bag sizes for vegetables lists the dimensions that go with each gallon size.

Garden soil is a poor fill for a bag. It compacts, drains badly in a container, and can carry weed seeds and disease. New Hampshire recommends a half and half blend of soilless potting mix and good compost, and the page on choosing a potting mix for containers explains what to look for in the bagged half. In open ground, University of Maryland Extension lists a soil pH of 6.0 to 6.5 as best for potatoes and 4.8 to 5.8 where potato scab keeps coming back, so there is no reason to add lime to the bag.

Set the bags where they get at least 6 to 8 hours of direct sun a day.

Choose and Prepare Seed Potatoes

Buy seed potatoes from a garden center or seed catalog in spring. Supermarket potatoes are often treated with sprout inhibitors, and both New Hampshire and Penn State advise against planting them. Penn State also advises against replanting tubers saved from last year’s garden.

Variety choice is different in a container. New Hampshire notes that container potatoes usually stay smaller than those grown in the ground, so small “new” potato types tend to do better than big russets. The same source prefers midseason and late varieties over early ones for containers, because they keep forming tubers over a longer period.

Small seed potatoes, 1 to 1 1/2 inches across, can be planted whole. Cut larger ones. Maryland’s guideline is a piece of 1 1/2 to 2 ounces, about a 1 1/2 inch cube, carrying 1 to 3 eyes. Let the cut pieces air dry for a day or two before planting, which New Hampshire says lowers the chance of rotting. Penn State suggests a single layer at 60 to 70°F for this step.

Pre-sprouting, also called chitting, is optional. The Royal Horticultural Society’s method is to stand the tubers in an egg carton with the eyes facing up, in a bright, frost-free place, until the sprouts are about 2 inches long.

Plant in the Bottom of the Bag

Plant in spring once the mix has warmed to 45°F, the minimum soil temperature given by both Maryland and Penn State. Then follow these steps.

1. Roll the sides of the bag down so the planting surface is easy to reach.
2. Add 6 to 8 inches of moist mix to the bottom.
3. Set the seed pieces on the mix with the eyes or sprouts up, about 1 foot apart.
4. Cover with about 6 inches of mix and water well.

How many pieces fit depends on the bag. New Hampshire’s rule is five gallons of soil volume per plant, which works out as follows.

Bag size	Seed pieces
5 gallons	1
10 gallons	2
15 gallons	3

The Royal Horticultural Society states the same idea by width: one seed potato for every 12 inches of pot diameter. Crowding in extra pieces is tempting, but each plant then shares the same limited volume of mix and water.

Sources differ a little on the cover layer. University of Illinois Extension suggests 4 to 6 inches over the seed potatoes, against New Hampshire’s 6 inches. Either leaves most of the bag empty at the start, which is the point.

Hill Up in Stages as the Plants Grow

Potato tubers are swollen stems, and Maryland describes them as developing at the ends of underground stems called stolons. Adding mix around the growing plant keeps those tubers covered and in the dark. Tubers that see sunlight turn green and should not be eaten.

As the stems grow, unroll the bag and add mix around them. New Hampshire’s rule is to leave about 6 inches of foliage showing each time. Illinois describes the same routine as adding soil until only the tops of the leaves show. Keep going until the bag is full.

For comparison, Penn State starts hilling garden rows when the stems are 8 to 12 inches tall. In a bag the timing is looser, because you are topping up loose mix instead of pulling soil from between rows. Check once a week and add mix whenever there is clearly more than 6 inches of stem above the surface.

Water and Feed on a Schedule

A bag dries faster than a garden bed. The target is mix that stays moist and never soggy. Push a finger in, and water when the top 1 to 2 inches feel dry. Apply enough that some runs out of the bottom, which shows the whole depth has been wetted. Penn State notes that garden potatoes get by on about 1 inch of rain a week, but a container cannot draw on surrounding soil, so the finger test is the better guide. The guide to watering container plants in summer covers how the routine changes in a heat wave.

Potatoes need a steady supply of nutrients through the season to make new growth and good tubers. New Hampshire recommends starting once the shoots are up, with a balanced soluble fertilizer every couple of weeks. It suggests a product whose middle number, phosphorus, is higher than its first number, nitrogen, such as a 5-10-10. Follow the label rate for containers.

Know When to Tip the Bag Out

Small, thin-skinned new potatoes come first. Maryland dates them at 6 to 8 weeks after planting, and the Royal Horticultural Society’s cue for early varieties is open flowers, with tubers about the size of a hen’s egg. Feel down the inside of the bag, take a few, and leave the rest.

For full-size potatoes, wait until the tops have yellowed and died back. Maryland recommends leaving the tubers where they are for 2 weeks after the plants die, which gives the skins time to toughen. Then spread a tarp, tip the bag over, and sort through the mix by hand. Handle the tubers gently, since they bruise. Brush off dry soil and hold off on washing until you are ready to cook them, because washing can damage the skin and lead to rot.

Potatoes meant for storage are cured first. Maryland’s figures are 10 to 14 days at 50 to 60°F and high humidity. Keep them out of the light the whole time to avoid greening. Penn State then stores them at 40 to 46°F and warns against going below 38°F, where sugars build up in the tuber. Green patches are associated with solanine, a bitter and toxic compound. Maryland says to cut green portions out and discard them, and the Royal Horticultural Society discards green potatoes altogether.

Penn State advises against planting potatoes where any nightshade crop grew in the previous 2 to 3 years. For a bag, that means spent potato mix should not go straight back under potatoes, tomatoes, peppers or eggplant. The steps for reusing old potting soil cover what to do with it instead.