Handling a Poorly Rooted Division
Bill Meyer, Woodbury, CT
   Sometimes when dividing a hosta a piece comes away with some rhizome but little or no roots. Other times pieces are rescued from a plant that is rotting off or chewed by voles. Still other times we may receive a piece of a plant from a friend or from an auction that is deficient in its underground parts. These are viable divisions which can be grown back into nice healthy hostas, as anyone will tell you. They will grow just fine and again become a full thriving clump. That much is true, because hostas are tough plants. Even with the worst handling, these poorly rooted pieces will probably survive.
   In this article, we'll look at two issues with dividing - when they are divided and how best to handle them afterwards. The best way to handle them can have dramatic results compared to poor handling. The first question to be answered is the time of division. 
   There are many views on the best time to divide which I feel are mainly the result of care after the dividing. Depending on how they are handled afterward there are different "best" times for division.
    If the intention is to divide a hosta and replace it back in the ground in a garden bed with no further effort, then they are best divided either before they leaf out or late in the season when they are nearly into dormancy. At either of these times, the hosta is in a state where it can adjust easily to the damage done to it with the knife. At this point in the growth cycle the roots are the important factor in how much the hosta will grow.
   Divided at these times, the plant will adjust by making itself smaller - producing less leaf material - because its damaged root system cannot provide as much water to the the leaves as an intact set of roots could. In turn the lesser amount of leaf tissue will lead to less root development as root development is tied to the amount of leaf tissue that must be supplied with water. The end result one year after dividing is a smaller plant that is balanced above and below ground.

   To get the best growth of divided pieces, the best time to divide is in the second half of spring just after the leaves have fully flushed out. This time gives the maximum potential, but it is only potential if they are not handled properly. At this point the hosta has finished making its first flush of leaves and is just going into the second part of its growth cycle. It is starting to make the roots that it will have next year. How much root material it will make will be determined by how much leaf material it has to supply water to. At this point in the hosta's growth cycle the leaves are the important factor in how much it will grow.
   If the leaves stay on the plant, it will develop roots to match before the season is over, leading to a fully rooted division that will increase in size from that point. It will go into dormancy with more root mass and emerge the following year with all the leaf material those roots can support. The end result is the biggest possible hosta one year later.

CHART SHOWING DIVIDING RESULTS

  TIME OF DIVISION AMT. OF ROOTS AFTER CARE RESULTS
In this chart the results of various dividing times with a lot of roots and only a few combined with care after dividing are displayed. 

EARLY SPRING means before the shoots appear to the time when they are starting to leaf out.

LATE SPRING refers to the time when the plants are fully leafed out. 

LATE SEASON refers to late August through fall into dormancy. 

AFTER CARE refers primarily to whether the plants receive too much sun and too little water 

1 LATE SPRING LOTS GOOD BEST
2 LATE SEASON LOTS ANY BETTER
3 EARLY SPRING LOTS GOOD BETTER
4 EARLY SPRING LOTS POOR AVG.
5 LATE SPRING FEW GOOD AVG.
6 EARLY SPRING LOTS POOR AVG.
7 LATE SPRING LOTS POOR POOR
8 LATE SEASON FEW ANY POOR
9 EARLY SPRING FEW POOR BAD
10 LATE SPRING FEW POOR WORST

   To accomplish the sort of root development on a poorly rooted division that is seen in the photograph, far and away the most important factor is keeping all the leaves intact through the entire growing season. If at any time before fall the division loses any leaves, or even large portions of leaves, the plant will stop trying to make roots to feed what was lost.
   The opposite is true for plants divided before the leaves are fully expanded. Damage to the roots at that time will cause the plant to stop leaf development almost immediately. Partially expanded leaves will stop developing as the plant responds to the damage by not building more leaf tissue than it can supply with water. If it continued to make more leaf material it would lose the energy it spent doing that when those leaves wilted and died.

   Keeping the leaves intact on a late-spring divided hosta is simply a function of preventing more water loss from the leaves than can be replaced by the damaged roots and rhizome. Water is drawn from the leaf surface through transpiration, which is similar to evaporation. If you think of wet laundry hanging out on a clothesline, you get the idea. The hosta leaves are full of water that is drawn from them continually and replaced by the root system. If the roots cannot supply water because they were too damaged, the leaves will quickly dry out like sheets on a clothesline. If the "plumbing system" can't keep up with demand the plant is in trouble.
   Dry air and most importantly direct sunlight pull water from the ground through the roots to the leaves and out of the plant. If it is pulled out faster than the roots can replace it you will see leaves wilting.
   Wilting is the first step in the plant's survival strategy. By wilting it reduces the amount of leaf surface facing the sun, which reduces the amount of water the sun is drawing from the plant. Hostas are not very good at wilting, so what little wilting they can manage doesn't help them much. They evolved in humid and rainy climates where wilting wasn't an important survival strategy.
   If wilting is not enough to prevent too much water loss endangering the whole plant, the second stage of hosta survival strategy will kick in - shedding. The plant will cut the flow of water to one or more leaves, allowing them to die so that the rest may live with the water it can supply. If a plant can't stay big, it will make itself smaller to survive.

Transpiration

Water is pulled up through the roots of a plant to the leaves where it escapes as water vapor into the air. As the water passes through the plant minerals and chemicals that we think of as fertilizer are left in the plant, which utilizes them to build tissue

   A poorly rooted division cannot handle much transpiration at all because its damaged roots are not close to being up to the job. The key to avoiding a survival response of shedding leaves is to reduce transpiration since we cannot increase the water the roots can take up. This can simply be done by potting the hosta and placing it where direct sunlight cannot touch the leaves. Total darkness won't work because the plant still needs to photosynthesize to make roots, so it should be potted and the pot placed under a tree or in some other spot where it will get only indirect light for the rest of the season. It should be kept watered but the key is to reduce how much water it loses.

   The picture accompanying this article was taken in September. The plant shown was a large single division cut in May on which the entire mass of roots had rotted away leaving only four stubs of the original roots. The rhizome was healthy except for a little rot around the cut. The roots that remained in May are marked with red x's in the photo. Given the size of the leaves, there is no way these few damaged roots could even come close to supporting the top if direct sunlight was drawing water from those leaves. Much sun at all would have probably reduced it to only one leaf if any before the new roots could grow. It might even have stressed it enough to kill the division. This situation is aggravated even more if those leaves were formed in a shady spot and they are then exposed to too much sun.
   What I did with this plant in May was to remove all rotted roots and clean the cut then treat the cut areas with a mild fungicide. I then potted it in ordinary potting soil with a little time-release fertilizer and put the pot under a tree and kept it watered. Because the sunlight never hit it directly it was able to keep all its leaves and build root mass over the season to match those leaves. After four months in shade it now has a root mass to match those leaves and will go into domancy that way. Next year it will put forth as much leaf material as those roots will support and grow on from there.   

The Bottom Line - Getting the Best Results 

Things to do:

 

Things not to do:

  • Wash all dirt off the division
  • Remove any rotted old roots
  • Scrape away any rotted rhizome
  • Allow cuts to dry in sun for at least an hour with leaves covered
  • Dust cut surfaces with mild fungicide
  • Pot the division and place where it will receive only indirect light
  • Fertilize with slow-release or repeated feedings
  • Plant in the ground late September on
 
  • Do not remove any leaves that still appear functional
  • Do not trim any healthy leaf tissue or roots away
  • Do not let direct sunlight touch the leaves
  • Do not let pot become overly dry
  • Do not overwinter in the pot

 

Reading Room
Library Homepage