Questions on: Rhubarb

Ron Smith, Horticulturist, NDSU Extension Service


Q: I bought a couple of Canada red rhubarb plants from a reliable source a few years ago. I deliberately chose Canada red rhubarb because I thought I would get rhubarb with red stalks. However, the stalks are green, not red. In the spring of 2006, I bought another Canada red rhubarb plant. I planted it in a raised bed and used a lot of organic material. The bed has good drainage and is in a location that gets morning sun and late afternoon shade. This plant also prospered and produced green stalks. I didn't remove any stalks last year, but I am cutting and using some stalks this year. I asked a plant specialist why I am getting green stalks, but he has no answer. (e-mail reference)

A: All I can guess is that the Canada red rhubarb is a clone that developed from a sport or chimera. When the grower divided the crowns for propagation and sale, the grower was unable to perpetuate the sport (the red stalks), so you end up with healthy, but green-stalked plants. Your best bet is to find someone who is growing red rhubarb and ask for a division. That way you are certain of getting the color you want.


Q: We have a hedge of dogwoods that are overgrown, so we need to prune them to the ground. Can we do it this fall or should we wait until spring? Also, I need to move some rhubarb. Can I do that this fall or is it advisable to wait until spring? What kind of soil amendments should we use? I have a morden sunset rose that had a bad case of black spot this summer and now has very few leaves. Can I cut all the canes down to about 6 inches and clean up all the mulch and leaves or is it a lost cause? (Cooperstown, N.D.)

A: You can cut the hedge back in late fall or early spring, but before new growth begins. Fall usually is preferred because the working conditions are better. The same holds true for rhubarb. Always add sphagnum peat moss because it will never hurt and always helps. For your rose, do the cleanup and next year use a systemic fungicide to control black spot.


Q: We moved to a home that has rhubarb in the garden area. I noticed that some of the leaves look different. We have determined that horseradish is growing near and in the rhubarb. Although I like horseradish, I don't want it growing in my rhubarb patch or yard. How do I move or eliminate it without ruining the rhubarb? (e-mail reference)

A: Horseradish and rhubarb don't mix well, but is difficult to separate. There is no way I can tell you how to separate the two without sacrificing some rhubarb. I only can encourage you to get this done as soon as possible before too much growth takes place. This will minimize the damage to the rhubarb.


Q: We have sold our house in central Minnesota and will be moving around December 1. Can I dig up our rhubarb, store it for the winter and then transplant it in the spring at our new house? If so, what is the best way to do this? (e-mail reference)

A: Yes, you can. Dig up the rhubarb before the soil freezes in your area. Immediately wrap the roots/crown in damp, unmilled sphagnum peat moss. Temporarily set the crown in the soil at the new home and moisten. It is OK if the planting mass freezes. Replant in its permanent location as soon as possible next spring. Make sure the area gets full sun and has well-drained soil.


Q: When is the best time to transplant rhubarb plants? Also, do you have any books out about gardening? (Carrington, N.D.)

A: Spring is the best time for transplanting, before new growth. I don’t have any books out, but I do have plenty of publications. A book is likely sometime in mid-2006. Go to www.ext.nodak.edu/extnews/hortiscope/contents.htm on the Web and work your way around the horticultural subjects of interest to you.


Q: I saw one question about where to get ornamental rhubarb. There is a list at www.plantea.com/rhubarb.htm. (e-mail reference)

A: Thank you for the listing. Our readers will appreciate having this source of information.


Q: I would like to know if you’re the one who I would talk to about planting asparagus and rhubarb together. I would like to know because I grow a lot of both, but I’m thinking about condensing my garden. (e-mail reference)

A: I certainly would account for space needs, especially with the rhubarb. One plant can spread and grow to 4 feet by 4 feet in just a few years. In our garden, we have 4-foot by 4-foot spots for both the rhubarb and asparagus. I find that the rhubarb leaves constantly encroach over the asparagus patch, requiring that the rhubarb be the first to be harvested.


Q: I have two large rhubarb plants in my vegetable garden. The leaves are huge and the stalks get long and thick, but they remain mostly green. Is this a different variety than the common red kind or are my plants not getting enough sun? Last spring I kept waiting for them to turn red, but they got woody instead. (e-mail reference)

A: Sounds like you have wild or common rhubarb instead of the valentine red.


Q: Last year we planted three rhubarb plants in a sunny garden area of what may have been a cow pasture more than 10 years ago. When the plants came up, the opened leaves grew fine, but had yellow patches on them. The rhubarb has come up again and the opened leaves have thinned areas that are reddish brown. One stalk has withered completely at the point it was attached to a leaf. What do you suggest? (e-mail reference)

A: I don’t know. It could be caused by pesticide residue, salts or a combination of both.


Q: I recently was given some rhubarb plants. I planted them in a raised bed. Can I plant herbs in the same area? I’m not sure if the rhubarb would taste like the herbs. I also wanted to plant some leaf lettuce on the other side. (e-mail reference)

A: You can plant anything you want around the rhubarb plants this year. However, as the years pass, rhubarb has a tendency to take over the area and crowd everything out, so enjoy the space while you have it!


Q: A friend gave me a huge, well-established rhubarb root, but told me not to cut it this year. I planted it with steer manure and it seems to be doing well. Should I heed the advice? (e-mail reference)

A: You don’t need to. Harvest a third of the stalks and keep on harvesting it as it grows. Stop around July 4 and allow the plant to grow through the summer. Harvesting late in the season tends to weaken the plant and the stalks don’t have the tenderness of the earlier harvests.


Q: Some years ago, we lived in a cottage that had a large rhubarb patch. We happily harvested rhubarb for many years. We now live in town, but I would dearly love to grow rhubarb again. The problem is space restriction and cats. Is it possible to grow rhubarb in a container? (e-mail reference)

A: Rhubarb easily should grow in a container. The container needs to be big enough to accommodate plant expansion. I wouldn’t put it in anything smaller than a 12-inch diameter pot, if possible. In this case, the larger the better. Be sure to put the container in a full-sun area. The more sun, the better. Use sterilized or pasteurized potting soil. I have never known cats to be attracted to rhubarb. If you want to make sure, plant a container full of catnip at the same time. I guarantee you they will go right for the catnip!


Q: My grandparents bought the house I live in back in 1925. A patch of rhubarb was there when they bought it. My grandmother, mother and now I have made many pies and rhubarb soup from this wonderful plant. I will soon be moving and want to take the rhubarb with me, but I have never transplanted anything. I have to mention that I will be moving to a pond area where I can only use certain types of fertilizer so I don’t pollute the pond. Do you have any suggestions? (e-mail reference)

A: It would be best if you could wait until after there has been a killing frost. If you can’t wait that long, then cut it back hard, divide the crown with a sharp spade and move it to the new location as soon as possible. Water it in well and use compost as your source of nutrients that will become slowly available and not leach into the pond water.


Q: We have a patch of red rhubarb that has been in the same place for years. The last couple of years the leaves start turning brown at the top and then spreads downward and the stalk gets limp. This starts happening in late June and gets worse from then on. Is there something we can do? (Wimbledon, N.D.)

A: Dig and divide! Throw out any part of the crown that appears diseased and treat the rest with Bordeaux mixture. Apply the treatment in early spring.


Q: My rhubarb is next to a large crop of raspberries. It seems to be dying out. Is there a problem here? Also, I have a vine growing in my yard that started in the neighbor’s yard and I cannot get rid of it. It’s climbing on everything and suffocating my other plants and flowering shrubs and is even climbing up my delicious apple tree now. I see sprouts coming up out in the middle of the yard. I've tried cutting the roots, etc., but nothing seems to help. (e-mail reference)

A: It is suggested that rhubarb be divided at three to five year intervals. Get together with your neighbor to develop a plan of attack to get rid of this pest before it swallows up your property - sounds like kudzu!


Q: We bought a house last summer that came with a lot of land. In the middle of about eight acres of grass is a small patch of what appears to be rhubarb. I am assuming it was there last summer, but it would have been mowed down. I love rhubarb and would like to move it elsewhere. Does it do better in the shade or full sun? Does it need dry or wet soil? (e-mail reference)

A: It is probably rhubarb. Since it is thriving where it presently is, why not mow around it this year? Early next spring, as soon as the soil can be dug, move it to a spot with similar conditions. Rhubarb thrives in full-sun and moderately well-drained conditions. If you can't wait that long, carefully dig up about a third of the stalks, with rootballs, and move them to their new home. Enjoy!


Q: I have rhubarb question for you. Is it possible to successfully plant the seed of rhubarb plants? (Dickinson, N.D.)

A: It should work, but I have never tried it. My references tell me the seeds should be planted a month before the last frost. Plant the seeds two inches apart, a half inch deep and hand firm the soil. Thin the seedlings so they are a foot apart. It takes 90-100 days for the plants to mature. The reference book says it is best if the seeded rhubarb is treated like an annual crop, as the plants that are allowed to go into their second year tend to bolt to seed stalks quickly. Plants that develop seed stalks directly, as the new leaves grow, should be culled out. I would suggest, for the sake of experimentation, the seed be placed in a refrigerator crisper for about 30 days. Then go through the planting schedule to see if the seeds germinate with that short a cold treatment. Leave some seed behind for another 30 days. Hope this helps!


Q: I just picked a large amount of rhubarb from a friend’s patch. Are the leaves toxic to animals? Our chickens love green clippings but I do not want to poison them. (e-mail reference)

A: Good thing you asked! Rhubarb is toxic to humans and I would think it would not be too good for chickens either. I would relegate the leaves to the compost pile if you have one.


Q: We had our rhubarb coming along quite well, but then we had at least two nights with temperatures down to the very low 20s. Can the frosted rhubarb be safely used or should it be discarded? (Cando, N.D.)

A: Don’t use it if the stems are mushy. Otherwise, there is no problem with frosted rhubarb. Ours in Fargo is just as vigorous as ever.


Q: I would like to know what to do with my rhubarb because it hasn't been doing too well. I don't want to transplant it, but I am wondering what kind of fertilizer I should use and when. (Roscoe, S.D.)

A: The fact that you are having a problem with your rhubarb is probably because it has been in one spot too long. When the leaf stalks don't attain the thickness you expect, that is usually the reason. The plants should be dug and divided every six to eight years to keep them vigorous.

You can try fertilizer; 10 10 10 using about a half cap per plant next spring, as new growth is just starting. That may be enough to pull them out of their funk.


Q: Would you please send me information on a mail order source for ornamental rhubarb and sorrel plants? (Lake Bronson, Minn.)

A: Much as I tried, I could not find any sources for you. Perhaps one of our readers will know of a source and pass it on to me. Sorry!


Q: My rhubarb was ruined by wind in late June. I pulled it out and now the new growth is young and tender but your last article said not to use anymore this year. I've heard before not to use rhubarb after July 15 but I'm wondering why? (Arthur, N.D.)

A: The leaves are needed for food production next year. Removing too much of the foliage beyond mid-July will reduce the carbohydrate energy the leaves can produce resulting in a weaker plant in future years. This would be especially true in your particular case because the plants were damaged early in the season. Be patient, you can enjoy it next season.


Q: My rhubarb plants got in the way of weed and mosquito spraying this spring. I pulled all the stalks and the new ones are coming out nicely. Will it be safe to use the new growth for freezing and canning this fall? (Litchville, N.D.)

A: I wouldn't. Give it a season to get over the trauma and do your harvesting next spring. I am sure you must have some neighbors or a local farmer's market that can provide you with enough stalks for your intended purposes.


Q: Can you pick and use rhubarb after it has gone to seed? (E-mail reference)

A: Yes, but you should stop picking it now. You should remove the seed head as it is developing. Seed production takes energy away from the vegetative production of the plant, which is what is wanted.


Q: My husband got spray happy, so in the process of spraying cocklebur he sprayed my rhubarb patch. He assures me you can't kill rhubarb. For his sake lets hope not! He used trimec. The rhubarb is curled but still green. We have had a great deal of rain. (Ellendale, N.D.)

A: Let me count the ways that husbands can place themselves on thin ice. This certainly has to rank right up there among the top 10! The rain will help. Your husband is wrong, rhubarb can be killed especially with a Trimec product. Tell him to not be so trigger happy next time.


Q: Can you tell me how to determine if some rhubarb growing on the edge of my lawn is safe to eat? (E-mail reference)

A: If it looks normal in every way, where it is growing should not make any difference.


Q: I would like to divide up and transplant my rhubarb plants. They have not been moved or divided for years. Is this a good time to do so and do you have any tips for doing it successfully? Also, I have something digging holes in my lawn. What ever it is seems to do it at night, digging small round holes and laying the grass beside the hole. I have a nice lawn and I am afraid this is really going to hurt my grass. Any idea what it is or what I can do? (Rutland, N.D.)

A: Dig and divide the rhubarb in the early spring just before new growth starts. Divide the plants into pieces that have one or more vigorous buds. Replant in soil well-worked with compost or peat moss and enriched with about a cup of 5-10-10 or something similar. Plant the buds 4-6 inches deep. It sounds like skunks are digging up your lawn looking for grubs before they go deep for the winter. Try trapping them in a live trap using an opened can of fishy cat food as bait. Then the tricky part is to get a tarp over the cage and get it moved without getting a dose of their unique perfume. To discourage skunks, leave the lights on or have something that makes noise on a random basis. They are not as persistent as raccoons, so a little effort in spooking them may work. Of course, if they are unsuccessful at finding any food, they will move on!


Q: Eleven years ago we dug a very small rhubarb plant out of the prairie by an old homestead. This one small plant is now 15 rhubarb plants with one that grows stalks of rhubarb to 3 feet high. This one plant is by itself in the middle of the yard and we let it go to seed each year as a "show plant." The leaves are always 2+ feet wide and just as long. The seed stalks grow to over 5 feet high and are a creamy white. It is just beautiful. We don't know the variety, but all the plants have more green stalks then red. It makes wonderful rhubarb pie and sauce. Some of the stalks are always 6 to 8 inches around. This homestead belonged to my family, and we all know that the rhubarb had not been disturbed in decades. Apparently some of the old time varieties, or at least this one, didn't need to be dug up and moved every so often. (E-mail reference)

A: Thank you for the information and history of the rhubarb on your family's property! I recently saw some that would equal what you describe on a trip to Alaska--a huge plant, taller than I am.


Q: Inquiring minds need to know! Is it safe to eat wild rhubarb? ( Cando, N.D.)

A: Yes it is, assuming it IS wild rhubarb. Unless you are 100 percent certain, you should stay away from it. Actually, rhubarb is an immigrant, landing on both coasts in the mid-18th century by Europeans and Russian fur traders to Alaska. When I was in Alaska recently I came across a plant that was more than 6' tall and at least as wide! What you are seeing is really an "escape" from cultivation.


Q: I was looking for a recipe for insect spray made from rhubarb leaves when I ran across your response to someone who maintained that they knew of a rhubarb patch that was 70 years old. Your response was that it was impossible. You maintain that it should be moved every six to10 years. I have a patch on my property that is at least that old, never been moved, never been fertilized, never had manure added and it still produces two crops of rhubarb in a year. My only problem with this patch is keeping it from spreading into a surrounding flower bed. This is what is left of a 30-foot patch that has taken me years to reduce. The soil that it grows in is a good light loam. It produces sufficient stalks to supply my wife and her friends with enough for pies, muffins etc. as well as the 20 pounds of rhubarb stalks needed to make my yearly 23 liters of excellent rhubarb wine. (E-mail reference, Ontario, Canada)

A: Send me some of that wine! And, I'll never use the word "impossible" again when it comes to gardening wonders. I just came back from a cruise to Alaska and saw a rhubarb plant that was over 2 meters tall and at least as wide, growing in a little cut-out between sidewalk and wall, with no obvious fussing. Never second guess the powers of Mother nature!


Q: I have a rhubarb sample that has leaf spotting on it. Is that typical of rhubarb? One stem has what I'd call worm feeding, which appears to have penetrated the outer layer. Then that area has turned brown like an exposed apple. Surrounding the brown is purplish area. ( Ellendale, N.D.)

A: It sounds like a leaf-spot fungus. If you have only one or two leaves affected, then simple removal of those leaves will suffice. If it appears to be spreading, then a spray with Captan is recommended, but the crop cannot be eaten for the balance of the season after that. Generally this disease is mostly localized and not lethal to the plant.


Q: The leaves on my rhubarb have holes eaten through all over and then marks on the stems. Some of the plants are no longer growing new leaves. I've sprayed, which didn't help. I'm afraid this is going to kill my rhubarb. (E-mail reference)

A: It sounds like you have some slug activity. Bug spray will not help. Pick up a slug poison or place some stale beer around in shallow pans to collect them.


Q: What causes yellow spotting on the leaves of my rhubarb?

A: Phytophthora root rot is the most common disease of rhubarb, attacking the plant crown, causing the stalks to rot at their base. It is characteristic of poorly drained soil. If it is just a stalk or two, I suggest cutting it off, and using the stem in cooking. If it reappears throughout the season, then send in a leaf to my attention.


Q: I am looking for information about growing rhubarb from seed. Do you have any information or suggestions? (E-mail reference, Williston, N.D.)

A: No and yes. No, I don't have any written information, and yes, my suggestion is to either have a ton of patience to grow it from seed, or simply propagate it by division. The latter is what I seriously suggest, as today's rhubarb is highly hybridized and the seed would not come true. So, if it is a particular quality that is wanted, the vegetative means is the only way to go. Otherwise, the quality will be quite variable.


Q: Previously I wrote to you and you diagnosed my strawberries as having angular leaf spot. We tilled some of our plants under before we realized that it is carried over in the soil. What can I plant in this spot now that won't contract this disease? I've been thinking about asparagus, but I'm not sure. (New Salem, N.D.)

A: Asparagus and/or rhubarb sounds like a winner to me! These two are fairly tough and dependable. 


Q: My rhubarb leaves have holes in them from a grub. What is the best way to treat them and when is the best time? Would it poison the stalks? (McIntosh, Minn.)

A: The critters you see feeding on your rhubarb are likely slugs. A sprinkle of salt on them will take care of those you hit. For the unseen others, get a bait know as "Slug-getta" and that will bring the population down significantly.


Q: In past years my rhubarb has grown thick stalks, but this year it is producing primarily spindly, thin fruit. What is causing this? (Killdeer, N.D., e-mail)

A: Rhubarb doesn't like to be kept in the same place forever, so when it gets sick of the location it is in, it lets us know by producing undersized petioles and leaves. Simply dig it up and move it to a new location. This needs to be done every six to eight years.  


Q: Can you tell me what I should do with my rhubarb that is already going to seed? Can I pick winter onions now? How do you know when they are ready to pick? (Williston, N.D., e-mail)

A: Rhubarb should not be allowed to flower and set seed. Cut the stalk off. Winter onions should be harvested in spring—now—so enjoy!


Q: Will Poast work in a rhubarb bed to get rid of grass? Also, when rhubarb sets its seed pod along with the stock in the spring, what needs to be done? (Fosston, Minn.)

A: Poast is a selective herbicide with a broad spectrum of post-emergent activity, especially suited for grassy weed control. In checking the extensive label, I find that Poast can be applied up to 15 days of harvest.

When the rhubarb sets the seed head, cut it out immediately so that photosynthetic energy is not wasted. We want it to all go into growing new stalks!


Q: Would you please tell me how to get rid of rhubarb? The couple who had the house before us planted several in a flower bed, which we would like to use for flowers. I've tried mowing them off, but they keep coming back. (Hecla, S.D.)

A: I am always amazed at some of the questions I get! Most people would be happy to have persistent rhubarb! If digging doesn't eliminate it, spray the leaves with Roundup. That should do it!


Q: I read an article that stated it was not good to plant rhubarb next to flowering shrubs. Could you tell me why? I have eight rhubarb plants growing about 5 feet from lilac bushes. I have always had good rhubarb. (Keldron, S.D.)

A: I know of no reason why rhubarb cannot be grown near any other plants. Your testimony certainly bears witness to that fact. No references I checked alluded to this problem either. I can give no reason why the author of the article you referred to would make that statement.


Q. My daughter-in-law has two red rhubarb plants that come up in the spring and leaf out and the next thing you see them dying and drying up. She said she did not get weed spray on them. (Jamestown, N.D.)

A. This sounds like it could be verticillium wilt, which is a very persistent soil fungus that can exist for many years in the soil as a saprophyte (a noninfectious form) before it finds an appropriate host to parasitize, such as the rhubarb.

Unfortunately, there is nothing to control it, except to get rid of the plants.


Q. We enjoy reading your column and get useful information from it.

I never thought you could kill rhubarb, but we lost one of our three long-producing plants two years ago. This spring we fertilized with barnyard fertilizer, but one hill was slow to come and was spindly and weak. Leaves turn red and dry up. I called Master Gardeners and county agents and they could give me no help. I was wondering if you could tell us why this is happening and what to do about it. I know of rhubarb hills well over 70 years old and still producing. Thank you. Frazee,  Minn.)

A. Rhubarb plays host to a number of diseases which can be fatal. In your case, the sample you sent had indications of Anthracnose and a virus, likely one known as turnip virus.

Anthracnose is spread in wet springs. The virus is transmitted via insect activity.

Thank you for the kind comments about the column. I have to take exception to your comment of 70-year production from one rhubarb plant. If this is so, it must have been moved several times. Generally, six to 10 years in one location is max.


Q. I have a question about my rhubarb plants. As soon as the plants get about 6 inches high they start sending up seed stalks, more than one in each plant. I keep breaking them off. Is there something I can do to eliminate them going to seed, especially so early. The plants are several years old, but have big long thick stalks.

I enjoy your page in the green sheet. (Pierre, S.D.)

A. There are several causes for heavy seed production. One is the gender, a high population of female plants. It may be that as the plantation ages, the female plants have increased. I assume you have maintained annual fertilizations so nutrient deficiency is not the problem.


Q. This note is to ask you to please send me information concerning the diseases of rhubarb and what to do about them. I know about the planting of the roots, but can't get it to over-winter because of root rot. I understand it is a cool-season crop but I still keep trying. I manage to get a pie or two.

Since my childhood was spent in North Dakota, I learned to love rhubarb pie. Thanks for your help. (Halifax, N.C.)

A. I have enclosed extension publication H-61, "Asparagas and Rhubarb." (Readers may obain a copy from any county office of the NDSU Extension Service.) If you wish to continue an attempt to grow it successfully in your state, you will have to "fool" it a little. Here is what I suggest:

1. Make sure the planting site is well-drained and rich in organic matter.

2. Plant it on the east side of your house where it gets only morning sun, or where it can get filtered shade during the heat of the day.

Even giving it the best of care in North Carolina, you will be lucky to get five years of productive growth.

Thanks for writing.


Q: Why would rhubarb plants set seedstalks first thing in the spring? (Towner, N.D., e-mail)

A: That simply proves they are sexually mature or established in their site. They should be cut off to preserve food for the stalks and new leaves.


Q: I have one bunch of rhubarb growing within a couple feet of the garden. In the garden I have a row of peonies on the outside. Near the rhubarb the peonies are
stunted and look unhealthy. Question: Does rhubarb do something to the soil that is possibly toxic? (Carrington, N.D., e-mail)

A: Yes, some plants do exude substances from their roots that are inhibiting or killing to certain other species of plants. This is called allelopathy;
turfgrass has a similar effect on young trees;

large trees like black walnut have an effect on plants in the nightshade family especially. Dig either the rhubarb or peony up in the fall and replant
somewhere else.


Q: When is the best time to transplant rhubarb? I have several red plants, but they only get pencil thin, It that the variety of rhubarb? Also, can I cut back the peonies now or do I wait until it freezes? Can I cut back lilies, iris, and painted daisies now? (Esmond, N.D.)

A: The pencil stalks usually indicate the plant needs to be moved. If you want to assure successful establishment, wait until either this fall or early next spring to transplant. Your peonies and bulb foliage should be kept on until a couple of frosts hit. Removing the foliage now would be like setting you down for a three-course meal, but making you stop after only one course! The plants will weaken and eventually die over the years if this practice is followed.


Q: I was wondering, what is the best time to move some rhubarb plants, strawberry plants and mums? (E-mail reference, Morris, M.N.)

A: The best time is: rhubarb, early spring; strawberry plants, spring; mums, in the fall.


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