Potato Bag Gardening: The When, Where and the How. . .

My Potato Bag

My Potato Bag

Potato bags are a boon to suburban gardeners like me. My property is in an older development with a not very large backyard. Most of the backyard is taken up by a swimming pool, so my planting options are more limited. What soil I do have, I want to keep healthy and arable.

One of the dilemmas facing a backyard gardener is where to grow your crops. It’s not always possible to dedicate large, contiguous portions of the yard to crop production. And, with the limited space, consideration must be given to how the planted crops will interact.

The potato is a crop that requires consideration. Planting potatoes brings the risk of verticillium wilt and late blight contaminating soil or crops. Once that soil is contaminated, it’s very difficult to clean up and that area is effectively off limits for future planting.

According to Laura Reynolds, writing for SF Gate/Demand Media:

Verticillium wilt and its ugly partner Fusarium wilt are fungal diseases that destroy home gardens as well as agricultural crops. They lurk in the soil, infecting selected vegetables and ornamental plants, causing leaves to wither and die. Although a simple soil laboratory test accurately diagnoses Verticillium, ridding your soil of the fungus takes careful management and lots of time.

Verticillium fungi target the roots of hundreds of species, many of them annual vegetables such as tomatoes (Lycopersicon esculentum), rhubarb (Rheum rhaponticum) or pumpkins (Curcubita pepo). The fungus enters feeder roots with other nutrients, then travels throughout the stems and foliage of the plant. It leaves withered, or necrotic, leaves behind, beginning from the plant’s bottom. As the plant dies, the fungus colonizes adjoining plants. Verticillium overwinters in decaying plant matter for up to 15 years, so one infected plant can re-infect an entire garden.

As a backyard gardener with limited planting options, I don’t want to risk infecting my soil and saying goodbye to backyard gardening. I enjoy it too much – both the activity of gardening, as well as the delicious results it brings.  So, I grow potatoes in potato bags instead of in a raised bed or in a corner somewhere in my yard. I want the potatoes, but I don’t want the potential problem of verticillium wilt destroying my soil.

Materials.  It’s very easy to grow potatoes in the bag. Here are the basics, courtesy of Gardener’s Supply, where I purchased my bags (FYI – this is not an intentional plug for Gardener’s Supply, but this is where I found the most helpful information):

  • Grow bag.
  • Seed potatoes. Buy organic seed potatoes. Cut the seed potatoes into five 2-ounce chunks — about the size of a lime. If your seed potatoes are small, you can plant them whole. A regular-sized bag holds three to five pieces.
  • Soil. The goal is a free-draining mixture; mix garden soil, topsoil and a little bit of compost. If you have heavy clay, then use a topsoil/compost/mulch mix. Put the soil in a wheelbarrow or tub that can hold it all at once. Moisten the soil and mix thoroughly. About one-third of the soil will get used on planting day. The rest will be used as the plants grow. Set it aside
  • Irrigation.  Hook up a drip irrigation line, if possible.

When/Where to Plant.  Plant potatoes when the danger of frost has passed. Select the sunniest site possible. All-day sun is best, but as little as 6 to 8 hours will suffice.

Planting the Bag.  Fold down the top edge of the bag to form a 4″ cuff. Fill the bag with the moistened soil mixture until it’s about 4″ deep. Place the seed potatoes on the soil surface, spaced evenly. Cover with another 3″ of soil.

Growing.  Once the plants have grown to about 8″, it’s time to add more soil. It’s OK if some of the foliage gets buried. Unfold the edge of the bag and add about 4″ of the soil mixture and water thoroughly.  Allow the plants to grow, adding soil after they’ve grown another 8″.  Repeat the process until all the soil mixture is used and the bag is full. This encourages the plants to make lots of potatoes, which form along the buried portions of stem.

The porous fabric allows the potato bag to breathe, which prevents overheating and overwatering. However, it’s important to monitor the moisture level in the bag because it can dry out quickly. The soil should feel moist, not soggy.

Colorado potato beetles are the most common pest. Inspect your plants regularly, looking under the leaves for the clusters of yellow eggs. If you see them, rub them off with your finger. Adult beetles are easy to identify — and control: Just pick them off with your hands and toss them into a bucket of soapy water.

Harvesting.  Potato plants usually look pretty shabby just before it’s time to harvest. The potato plant will flower and grow vigorously through the summer. Toward the end of the season, however, the leaves will start yellowing and the stems will wilt. At this point, stop watering and wait a week or two. After that, the potatoes are ready to harvest.  Now, dump the bag — plants, soil and all — into a wheelbarrow or onto a tarp. Dig through the soil and pull out the potatoes. You can expect to harvest about 7 lbs. of potatoes, although you could get as much as 13 lbs. in a good year. Clean out the bag and save it for next year.

Gardener’s Supply recommends reusing the soil next year or putting it into your garden. Given the concern over verticillium wilt or blight, I would modify this recommendation: before reusing the soil, make sure there are no signs of blight or fungal wilt.

Next up, treating/using infected soil. . .