This page outlines the basic information related to rhubarb and where/when/how to plant and harvest, a few growing techniques (including forcing indoors), and diseases and insects.

WHERE TO PLANT RHUBARB 

Rhubarb is a robust and prolific plant in the right climate and soil.  It is a cool-weather perennial.  Rule of thumb:  it will do well provided the mean summer temperature is below about 75^o and the mean winter temperatures is below 40^o.  The plant needs 2 months of frozen ground for a proper rest period during the winter.  Under those conditions it will normally have no diseases or pests...making it ideal for organic techniques.  It prefers well drained soils unusually rich in decomposed organic material...twice as rich as most other plants would want.  For best results the rich soil should be at least 12" deep, 36" in diameter and 30-50% organic material.  Earthworms help, too. Rhubarb prefers slightly acidic soils but is tolerant of a wide range of pH and soil conditions, provided it drains well.

 

Most rhubarb varieties first mature within 2 months of the start of the growing season.  The rhubarb season starts as soon as the ground is thawed and the days are consistently above freezing, which is March/April in Black Forest, CO.  It can easily endure freezes and snows during the growing season but cannot tolerate temperatures approaching 100^oF for very long at all.   In high temperatures it will wilt to protect the plant...to keep it cool.  Wilting does not damage the plant but no growth takes place while the plant is wilted.  In response to prolonged periods of heat, however, the plant will simply give up.  It grows best in the higher elevations of Colorado and in northerly states such as Michigan and Washington state...places where most homes require no air conditioner at all.  These are generally categorized as agricultural zones 4 or 5.   In warmer climates such as Oklahoma, Texas, or the South rhubarb frequently fails to survive even one summer.  Unfortunately, the plants need two years good growth to produce viable harvests.  Consider that together with their intolerance of warm weather and you can only conclude that rhubarb is altogether unsuitable to outdoor growth in warmer climates...they simply are not a viable annual.  However, the plants can be forced indoors with acceptable results.  Indeed, this was the preferred way of producing rhubarb during the heyday of its culinary popularity.  Forced plants were reputedly milder and better tasting.  (See below for more information about forcing rhubarb.)

 

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For the shortest time-to-harvest and the most likelihood of a plant true to the parent you should elect to plant freshly dug root stock from large, good tasting, healthy parents.  For best results transplant roots in the spring just as the new shoots are beginning to grow.  For the most reliable results ensure that each root has the bud of at least one growing stalk (though this is not absolutely necessary, it increases chances of success).  (See phases of growth, "one week after compost blanket removed" for an idea of what the plant should look like when dividing the roots.)  Seeds also work but do not often breed true to the parent...you might get better, might get worse.  Start seeds indoors two months before the planting season.  Start them as you would any large plant...begin in small trays, transplant to pots as they get their first real leaves, etc.  Transplant as soon as danger of snow has passed and the ground is thawed.  Plant 5 to 10 seeds or freshly started seeds within a circle several inches apart wherever you want one plant and thin any undesirable roots as their nature is revealed.  Hopefully, the stronger, larger plants will overwhelm any puny relations and dominate the new growth.

 

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WHEN TO HARVEST:  Harvesting any significant amount from one year old plants (two or three years old if started with seeds) is ill advised.  You'll weaken the plant and be very disappointed in future harvests.  For best results pamper the plants for two years of growth before harvesting.  In the third year of healthy growth the plant will be large enough to provide a substantial harvest and still continue growing to larger sizes in future years.  You can begin harvesting as soon as the stalks are suitable sizes.  Note that the victoria variety, mostly green on the outside, seldom turns completely red.  Use size and texture to indicate harvest-readiness rather than color.  The stalks should be firm and typical size for your variety (Size varies enormously by variety and there are well over 60 varieties!)

 

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Encircle your target stalk below the leaf with your hand.  Gently slide your hand down the stalk to get as close to the base as possible.  Tighten your grip, pull straight out and simultaneously twist and bend about 1/4 turn, 45^o, respectively.  This technique will reduce the risks of either pulling up the root or breaking off the stalk above the root connection.  You want the stalk to break off from where it attaches to the root.  This will make room for another stalk to replace it later this season.   Harvest no more than 50% of the biomass of each plant in each harvest.  Such maximum harvests can be made two, three or four times a year, depending on your goals and growing technology.  Such harvests should be 5-8 weeks apart.  If you simply can't wait two full years you can often harvest about 1/4 of the biomass during the second year without significant impact on future growth...but this will not be a very large harvest and you're best advised to be patient and wait another year.

 

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Rhubarb is ideally suited to organic growing provided the fields are properly prepared BEFORE planting.  See the details of our techniques for one suggestion.  Growing organically, however, does place smaller limits on the harvests than those of non-organic techniques.  We get at most two high quality harvests per year, about 6-8 weeks apart, taking 50% of the biomass each time with the second yarvest yielding about half the pounds per plant as the first harvest.  Going beyond that would stress the plant beyond the soil's ability to fuel a recovery with continued growth and equally large future harvests. 

 

We also have experience with non-organic approaches.  Fertilize the root area and surrounding soil once a month with a hand full of good vegetable fertilizer.  Water weekly.  You'll be able to harvest about every 4-6 weeks until the plants give up for the season or harvest smaller amounts continuously during the growing season.

 

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"Forcing" refers to any process designed to produce a harvest, or blossoms, in conditions ostensibly non-optimal.  For rhubarb it is the process of growing rhubarb indoors at temperatures and in soil similar to their ideal outdoor conditions but in considerably less light.  The roots are often selected from 2+ year old plants, often grown outdoors.  If outdoors, then the roots are often transplanted when the plant goes dormant for the winter.  In those conditions, however, the roots must be allowed to rest for at least 5 to 6 weeks before they can be stimulated to resume growth.   In colder climates suitable to rhubarb this normally involves digging, splitting and planting root stock in deep pots or raised boxes in late Fall or early Winter, after the plants have been dormant for weeks but before the ground freezes solid.  If outdoor conditions don't allow sufficient time for the plants to rest then they can be transplanted indoors earlier.  In that case, the room should be kept at or below freezing for 5-6 weeks, to allow the plants to rest indoors before resuming growth.

 

The roots can be buried under a few more inches of soil than is recommended during normal planting and, to resume growth, the room can be brought to and kept at 55^o to 60^oF.  Never allow the temperatures to approach 70^o or you risk exhausting the plant and reducing the quality and quantity of your crop.  Forcing is normally done in dark, cool cellars or by inverting empty, large pots over the top of a potted rhubarb if the room is otherwise lighted.  The resultant stalks will be lighter in color, more tender and milder in flavor than normally produced by the variety outdoors.  Indoor growth rates and yields, however, are considerably less than outdoor production.  Greenhouses can be used to force rhubarb.  However, the harvest will be similar to those produced outdoors.  Rhubarb forced in darker conditions is generally considered of superior quality to outdoor harvests so greenhouse production has always been uncommon.  If growing in a cellar or room with windows the windows should be virtually blacked out. Otherwise, the stalks will contort themselves toward the light and be quite unusually shaped and difficult to handle.

 

Keep the beds moist.  Production will fall off sharply in beds that become dry.  Harvest is generally within 2 or 3 months of the start of growth.  High humidity is also a plus.   Decreasing intensity of the stalk color is a sign the roots are becoming exhausted.

 

Forcing was common commercial practice during the peak of rhubarb culinary popularity. 

Forcing in the U.S. essentially ended with World War II but remains in commercial use in Britain.  Research into forcing was once conducted at Stockbridge House Experimental Horticultural Station at Cawood, Selby, North Yorkshire, England.  Details of their work have proven tough to come by.