Compost and potatoes have a complicated relationship.
If you want to compost potatoes, it will be somewhat risky and require a more active composting strategy. However, if you want to grow potatoes in compost, you’re on track for growing stellar spuds.
If you’re wanting to grow potatoes, you will probably end up composting them. So, we’re going to cover both topics in this article.
Can You Compost Potatoes?
Potatoes are a finicky crop. They are prolific, easy to grow, and store well. However, they are susceptible to many diseases; specifically potato blight.
Potato blight is a fungus-like, spore-borne disease that infects the foliage and stems of plants in the Solanaceae family: potatoes, tomatoes, and peppers, although potatoes are the most vulnerable. Depending on how long a crop has been exposed, it can also affect the tubers.
Spores reproduce on wet foliage and quickly produce swarmers, which infect the leaf tissue. During humid or wet conditions, spores will become airborne and settle on other damp foliage. As blight progresses, dark brown lesions are visible on leaves, and brown rot develops on stems.
Spores grow on the underside of lesions and are identified as a white, downy growth. Water can wash these spores down onto lower leaves and into the soil, where they infect the tubers.
Blight can quickly defoliate an entire crop. Once the spores are in the soil, you should wait at least four years before planting potatoes, tomatoes, or peppers in that same soil. Because the spores are able to survive many different weather and temperature conditions, this can make composting potatoes risky business.
Composting store-bought potatoes should be safe if you use an active composting process and do not put infected potatoes in the compost pile. Blight is easy to recognize in a tuber; if it has sprouted, or if you cut it open and see brown spots or any rot or mold, throw it away. Do NOT add it to your compost pile.
Since you probably won’t compost perfectly edible potatoes, the only remaining potato pieces you might add to the pile are potato peels. To reduce the risk of spreading blight, store potatoes in a cool, dry area, and wash them thoroughly before peeling. Do not add peels from potatoes with brown spots or rot.
If you are confident that you have a pile of perfectly healthy potato peels, you can add them to an active compost pile.
Composting home-grown potatoes is slightly different. The same rules apply for potato peels, not composting brown or rotted potatoes, and storing them in a cool, dry storage area.
However, if you are growing potatoes, you may also want to compost the potato foliage. This can be risky since blight is much more likely to be on foliage than on tubers. Blight cannot survive on dead plant tissue, but spores can remain active in soil.
If your compost pile does not reach adequate temperatures, spores can survive the decomposition process and spread to the rest of your garden as you incorporate your compost into the soil.
Foliage should only be used in compost if it is completely free from disease.
Active composting is the best way to successfully compost potato remains, or the remains of any other plants in the Solanaceae family. Active composting is the process of building a compost pile that is actively decomposing at all times.
Many gardeners throw pruning waste, weeds, leaves, grass clippings, and spent plants in a pile and wait for it to compost itself. This is perfectly fine, and will work eventually, but this is not a viable solution for composting potato waste.
Active composting is an intentional structuring of a compost pile that facilitates decomposition. It accounts for all five factors of successful composting:
- Green & brown balance. Successful compost piles have a mixture of two parts green to one part brown organic material. Green material is high in nitrogen, while brown material is high in carbon. Both are necessary to break down material quickly.
- Small particle size. Microbes live on the surface of organic material, and smaller particles provide more surface area, which gives microbes more opportunities to break things down. Shred or chip material before adding, but make sure it is still large enough to allow air and water to penetrate.
- Moisture. Without proper moisture, microbes cannot work their magic. To keep a compost pile actively decomposing, you may need to water it to maintain moisture. However, too much water can create anaerobic conditions where oxygen is no longer available and rot begins to form.
- Aerobic activity. Aerobic microbial activity requires oxygen and feeds a healthy decomposition of organic material. The opposite would be anaerobic, where no oxygen is available and harmful bacteria grows rot and mold within the compost pile. Add oxygen into the pile by inserting pipes, adding some bulky material (like wood chips), or turning the pile with a pitchfork.
- Temperature. If the first four conditions are met properly, it will result in the correct temperature for healthy decomposition. You can monitor compost temperature by buying a thermometer. Temperatures should be above 140° for proper composting.
While properly-heated compost should destroy spores, it is not guaranteed, and you may spread blight to your entire garden if the spores survive the composting process.
Using composted potatoes is only risky if you plan on growing anything in the same family. Potatoes, tomatoes, peppers, nightshades, and some flowers could all be affected by blight. But, if you plan on using your compost in a landscape bed, then blight is not a concern.
As a general rule, only compost plant material you know to be disease-free, and burn or destroy plant material that has been infected. This will help keep your compost pile free from all diseases and will give you a high-quality compost you can use in any area of your lawn or garden.
Planting Potatoes In Compost
If you want to plant potatoes in your garden, there are two key factors to your success: rotation and nutrition.
Blight is capable of surviving in soil for long periods of time, so a rotation schedule can help prevent buildup and allow soil to repair itself after an infection. The same rule applies to all plants in the Solanaceae family, so you cannot plant tomatoes in last year’s potato plot.
Potatoes are also heavy feeders, meaning they require a lot of nutrition from the soil. This is another reason for consistent rotation, as planting potatoes in the same plot each year will quickly deprive the soil of vitamins and minerals.
Because they are heavy feeders, compost makes a great growing medium for potatoes. Compost is very high in nutrition, and is therefore generally used as a soil amendment, since most plants have average vitamin and mineral requirements.
Plants in the Solanaceae family, however, need much higher quantities. Planting in compost can supply the plants with adequate nutrition and a healthy soil structure that promotes proper drainage.
Planting potatoes in containers with compost can also help alleviate blight issues. If you are growing a small amount of potato plants, you can fill containers with compost and plant directly in the containers. When it is time to harvest, the potatoes will be much easier to access, and you can simply discard the compost at the end of the year.
This can help reduce blight infections in the soil. Also, healthy plants are much less likely to be vulnerable to blight. Growing in compost will provide the plants the best possible soil conditions for healthy growth, therefore lowering the possibility of an infection.
Make sure containers are at least 3’ deep and 3’ wide, and that they have adequate drainage to prevent rot.
The best compost to buy for growing potatoes will look like soil
If you find recognizable organic material, like wood chips or leaves, you should not use it in containers.
If you’re using composted manure, make sure it has aged at least one year before using it in containers. Manure that is not fully composted will continue to decompose in containers, and this can cause your tubers to rot.
Make sure the compost you purchase is free from blight. Some composting methods, like vermicomposting, do not reach the temperatures needed to destroy some diseases. The best compost for growing potatoes will be a mixture of organic materials.
Best Potato Planting Practices
Whether you decide to plant your potatoes in compost, containers, or directly into your garden bed, there are a few planting practices that will help prevent blight and give your potatoes the best chance at a healthy harvest.
Buy certified seed potatoes to ensure you do not introduce blight into your soil. Spores can survive on dormant spuds, so buying blight-free tubers will help prevent an infection. Store-bought potatoes can be used for seed, but the chance of blight is much higher, so it is not recommended.
When you buy your seed potatoes, look for varieties that are blight-resistant or at least less vulnerable. Almost all varieties provided by reputable seed suppliers will have some level of resistance, but do some research on the potatoes you want to plant before you introduce them to your garden.
Chit seed potatoes to help prevent blight and make sure your plants are healthy. Chitting is the process of sprouting your potatoes before you plant them. Check a planting calendar for your climate to determine when to start your potatoes.
Find a container that allows you to arrange your potatoes in an upright position with adequate space between them for air circulation. Egg cartons work well for this. Then, place each potato with the eyes upright.
Place the container in a dry, well-lit space that stays between 50° and 70° for four to six weeks. During this time, the potatoes should produce shoots. A few days before planting, you can cut the potatoes into smaller pieces, but make sure each piece has at least three shoots. Smaller seed potatoes may need to be planted whole.
Plant the potatoes carefully to avoid breaking off the shoots. The chitting process allows the seed to be planted at a later date and after sprouting, which helps prevent rot and therefore prevent blight.
Plan your vegetable garden to minimize blight. Different varieties will be vulnerable to different strains, so alternating rows of potato varieties, or alternating potatoes with plants from a different family, can help reduce the spread of infection if you do happen to get one.
Also, plant potatoes far from tomatoes and peppers, and try to find blight-resistant varieties of these as well.
Potatoes are a fun and rewarding crop to grow, and with the right management practices, you can help keep your garden disease-free and healthy.
For more information on how compost improves the health of your soil, click here.