By: Mary H. Dyer, Credentialed Garden Writer
Tuber rot diseases are a major cause of crop loss, particularly affecting potatoes, but also carrots and other tuberous vegetables. Tuber rot in plants also poses a serious threat to hyacinths, bearded iris, cyclamen, dahlias, and other tuberous plants. Read on for common types of tuber rot and what you can do.
Tuber soft rot problems may be bacterial but are most often caused by various fungi. Tuber rot in plants is difficult to control because the rot can live on contaminated equipment and can lie “in wait” in the soil throughout the winter. Tubers damaged by disease, stress, insects, or frost are most susceptible.
Start with good quality, certified tubers. Inspect tubers carefully before planting. Dispose of soft, mushy, discolored, or rotting tubers. Always work with clean equipment and storage facilities. Sanitize all cutting tools. Use sharp blades to make a clean, even cut that will heal quickly.
Never plant tubers too closely and don’t allow them to become overcrowded. Don’t overfeed tuberous plants, as too much fertilizer makes them weak and more susceptible to rot. Be especially careful of high-nitrogen fertilizers. Avoid overwatering, as rot needs moisture to spread. Store tubers in a dry, cool, and well-ventilated area.
Consider planting in raised beds if soil drainage is poor. Dispose of contaminated plants and rotting tubers to prevent spread. Never put contaminated plant material in your compost bin. Rotate crops regularly. Never plant susceptible plants in infected soil. Control slugs and other pests, since damaged areas often allow rot to enter tubers. Avoid harvesting tuberous vegetables when the soil is wet.
Fungicides may help control some types of rot, although control is usually limited. Read the product label carefully, as it will tell you which fungus the product is effective against and which plants can be treated. It’s a good idea to check with your local cooperative extension office before using fungicides.
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Dahlias are brightly colored flowers native to Central America. These plants, which come in a variety of shapes and sizes, are treated as perennials in zones 7 through 11. For cooler climate zones, the tuberous roots (known as tubers) must be dug up in fall and stored over the winter. If dahlias are stored in a damp location, mold can grow on the tuberous roots. If the tubers haven’t become soft with rot, you can save them by treating the mold and storing them properly.
Rinse mold away carefully under running water.
Inspect dahlia tuber for soft areas that indicate rot. Slice off any soft areas with a sharp knife, leaving the eye of the bulb.
Discard any tubers that have rotted in the eye section. These will not grow.
Mix a solution of 10 percent bleach and 90 percent water in a bowl.
Dip tubers in bleach to kill any remaining mold spores.
Lay down newspaper in a dry, dark place. Put tubers on newspaper to dry.
Fill a brown paper bag with sawdust. When tubers are dry, place them in the paper bag and fold the mouth of the bag closed. Tubers should be completely buried in sawdust and should not touch one another.
Place bags of tubers in an empty milk crate so that there is plenty of air circulating through the crate and bags. Place milk carton in a dry, dark place with good air circulation to store until time to plant them.
Check your tubers every two weeks to ensure that mold has not returned.
You should always wear rubber gloves when handling chemicals such as bleach.
Ok. I will try keep this short and simple. I am trying to figure out what to do with this whiskey barrel I had planted Dahlia tubers in.
Last year I grew a Mystery Day Dahlia in the container. It grew well all year. By fall I was overwatering the container because the summer heat had faded and the water was starting to build up. I didn't notice immediately until the container had become quite mushy with water. I hoped if I didnt water it it would dry out. It slowly did but then one day my Dahlia had almost completely flopped over. I knew this was a huge problem so I pulled the plant out immediately. The tubers were all mush. I was annoyed but learned a lesson about whiskey barrels and being more aware of the watering.
That takes us to this spring. I planted an akita in the same pot. Same dirt. I wasn't too concerened about it because until now it hadn't occured to me I might have some type of pathogen in the soil.
Well the plant started growing and was 4 inches tall until it flopped over. I immediately thought oh no and pulled it out and to my horror the tubers were mush. I did not water the container and the dirt although fairly moist was not soggy. It had been raining for weeks though so it might never have dried out at any point.
So my question is this. Is this happening most likely due to enviromental conditions or could this be a pathogen in the soil? I don't want to plant another tuber just to have the samething happen if it is actually in the soil and the moisture now. Any opinions are welcome. I am not sure if such pathogens exist that would cause this but I thought I would ask.
I should also mention I have three of the same containers in different positions and all have had dahlias in them the past two years and this is the only one to have this problem. It is also the only one though that is not under an overhang and gets plenty of water from rain and gets morning and evening sun but not the hottest afternoon sun. The other two do not get rain water and do receive less morning sun but do get all afternoon sun.
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The one in the ground was rotted with a single stalk trying to grow but it literally pulled right out from the center of the bulb leaving a hole. The rest of the bulb was rotten and mushy in the middle.
The one in the pot was all roots and no bulbs! Last year it was a huge, healthy bulb.
The one in the pot had poor drainage so perhaps that could of caused it. But in the ground was good drainage so it makes no sense.
Last year both plants were big and had multiple blooms. I did fertilize very often all year, perhaps I over fertilized and the plants were absorbing the bulb for leaf nutrients and the winter did them in with little or no scales left?
When in the season do you fertilize Lilys and stop?
I would have say your bulbs rotted from issues dealing with excess moisture, on some level. I live in Seattle where it rains 9 months a year and we rarely have rotting bulb problems, so im a little stumpted here. perhaps there was something else going on as well. we have lilys in pots that we leave outside all year long in regular potting soil, as well as having bulbs in the ground, and rarely do we not have one come back. the lily's in the pic below have been in that cedar box for several years in a row, without so much as even touching them- no rotting problems what so ever. at the time this pic was taken they had been in there for probably three years in a row. we finally dug them up this year to divide them. they were in perfect condition. sorry I wasn't much help. I just don't have much experience with rotting issue because we don't get it too bad here. perhaps someone else can lend you a little insight.
Follow Jason's recommendations for feeding times it's a good one, although the fish emulsion can be substituted with a light application of 5-10-5, if you wish.
Be sure all your pots have good drain holes and don't forget to tip your pots sideways in winter for drainage because if left upright, those drain holes freeze shut resulting in a pot of freezing/thawing/freezing/thawing mud come the spring thaw. That will kill your bulbs, for sure!
The first thing you need to do is decide which potato varieties you may be interested in and how much room you have to grow them. We have a great climate in Alaska for growing spuds as they like a lot of direct sun and cooler temperatures. At the end of this writing, I will provide a list of some of the more popular determinate and indeterminate varieties we Alaskans seem to grow.
As I mentioned before, I grow all my potatoes in containers, mostly five and 10 gallon fabric bags as they are easy to move around and are really easy to harvest. I just turn each bag out into a wheel barrow and seek out the spuds. It’s a lot easier on the back and my harvest rates are consistent with in the ground growing, of which I have done also. Moose also don’t like potato plants and the bags can be placed anywhere outside my garden proper without fear of being continually topped by those pesky but majestic creatures.
As far as your soil is concerned, be it in ground or in containers, potatoes like an acidic soil so be sure you don’t add lime prior to planting as an alkaline soil can cause scab and other problems with tuber growth. Spuds like a soil with a pH in the 5.0 to 5.5 range. Our peaty soils make that easier for us but there are additives you can use to drop the pH if necessary, like garden sulfur. They also like a good loose growing medium and soil that compacts like concrete will produce smaller tubers and wear you out harvesting them. I use about 25% sand, 25% topsoil, 25% peat, and 25% compost. This mix allows for good drainage and a less resistive soil making it easier for the tubers to grow.
Potatoes like more phosphorous and potassium than nitrogen and too much nitrogen will give you a lot of leafy growth with poor tuber production. A good 5-10-10 should work well in your ground or containers for a successful spud production. I also throw in a little wood ash to the mix for a little extra potash.
Potatoes also hate to be soaked all the time, so be sure your soils are well draining and if growing in containers or bags, be sure excess water can drain off. If we start getting too much rain and my containers are getting soaked where I think my potatoes could rot, I will pull a big piece of plastic over all the plants to let some light in but keep the excess rain out. This has always worked for me.
Most potato growers know that when their plant vines start to yellow and wilt, the potatoes are getting close to harvest time. You can actually harvest your spuds at anytime but cutting the vines and letting the tubers sit underground for 10-14 days will help harden them off and they will store longer. If they are planted in the ground and it looks like a lot of rain is on the way, you can dig them up and store in a cool dry dark place for a few weeks and that will do the same as leaving them underground. Some people wash their spuds when they harvest, some don’t, and I have done both without noticing any difference in each crop. If it looks like rain and I’ve cut all the vines from my container plants, I will cover with a tarp or plastic to keep the soil from getting soaked and rotting my crop.
I really had no intention of mentioning how to actually grow potatoes from planting to harvest as the University of Alaska Fairbanks Cooperative Extension Service has a great publication for anyone wanting to grow potatoes, especially the novice grower. The only thing I don’t like about the publication is they don’t mention the different planting styles for determinate or indeterminate potatoes, but the publication is great for describing the general process of planting potatoes.
Field of flowering potato plants
One controversial topic between gardeners are the flowers on a potato plant. Their flowers are rather attractive and some gardeners swear that you need to pull the flowers to get larger spuds and others say no. I did both in 2020 and did not see any difference in productivity or size in the varieties I grew. I also did a little research and found several studies to determine if leaving or taking flowers off makes a difference. The study reports were fairly inconclusive and the results stated growth is more related to environmental conditions and variety grown. You decide though and if you want to remove them, do so, or leave the flowers on…it’s up to you. Imagine though trying to nip off the flowers in this field of potato plants. It may be easy for the home grower, but not feasible for commercial potato fields, and it doesn’t seem to affect their harvests.
I’d like to mention one issue before listing some common determinate and indeterminate varieties. Potato plants will develop small berries on them that look like tiny tomatoes. These are the potato true seeds and can in fact be grown into potato plants, but it is a lengthy process. The berry like fruit should be pulled off your plants and discarded if you have small children around who like to eat everything in the garden. These berries are very toxic and small hands sometimes can’t resist them, so please be careful if you have small children or grandchildren around.
Now a few popular potato varieties
(Short Season 70-90 days) (Long Season 105-140 days)
Yukon Gold Adirondack Red German Butterball Century Russet
Chieftain Adirondack Blue Russet Nugget Ranger Russet
Caribe Sierra Gold Strawberry Paw Russet Burbank
Norland Sierra Rose Alturas French Fingerling
Ratte Red Norland Green Mountain Magic Molly
Russet Norkota Canela Russet Red Pontiac
This list is by no means an exhaustive list of what you can grow in Alaska. Practically any variety can be grown here given the right growing conditions.
Have fun growing potatoes and try different varieties. Harvest at different time periods to learn how your plants grow. Competitive growers will pull their plants being careful not to break the tubers from the stolons, remove all the smaller spuds leaving the biggest tuber, and replant the entire plant with one good tuber in an effort to grow a giant competition worthy spud. The current world record potato was grown in the United Kingdom by Peter Glazebrook and it weighed in at a monstrous 11 pounds. He definitely can be categorized as a man with a passion for potatoes.
Photographs and drawings are in the public domain.