One of the highlights of the Master Gardener plant sale every spring is the throng of people that parade in early on Saturday morning to get the first pick of fresh pulled rhubarb and rhubarb plants. Betty Kizer of the Seneca County Master Gardeners is definitely the queen of rhubarb in that area, masterfully handling the peoples questions on growing rhubarb and how to harvest the rhubarb, which she discourages for the first three years to allow the plants to generate enough strength in the root system to sustain repeated harvesting with restraint. Many people attending the sale learn that overharvesting and under feeding are the two main culprits to rhubarb plant failure. I can hear Betty talking, telling one after another that you need to feed rhubarb, “it’s a heavy feeder”. But why is rhubarb different than most plants, I kept the question in the back of my head until I ran across the answer in wonderful book, Roots Demystified by Robert Kourick.
This book showed a section of the roots of a rhubarb plant in figure #30 on page 60 which I have included to you, it explains that rhubarb plants can generate a massive root system, as much as eight feet wide and eight feet deep in loamy soil. As many of you know we suffer from heavy clay soil, which impedes the growth of such massive root systems, but none the less there are a few things we can do to help generate larger roots and healthier plants.
As with many plants, the older roots at the base of the stem are less important in absorption of nutrients as the young roots in other areas of the plant. As many plants do not reach the size of the behemoth shown in the illustration above, it does become critical to feed the roots in the area outside the foliage as that is where the majority of the nutrient absorption is taking place. You can create an optimum condition for root growth by feeding the ends of the roots system, helping them to explore new areas of growth, while keeping in mind that as the root system grows in size so does the nutrient requirements. So feed according, increasing the nitrogen rich fertilizer and manure compost as the total root size increases. A general rule of thumb, start from the root growth area and fertilize outward half again as large as foliage of the plant. As winter approaches, deeply mulch over the whole root system especially over the crown of the plant, this will help to protect the plant from freezing while also insulating the ground to give the root system a quicker start in the spring when the mulch is pulled away.
With personal and professional regards - Vince