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Divide Your Hostas in August or Early September
By Bob Solberg (president, Green Hill [hosta] Farm, Chapel Hill NC)
One of the most frequently asked questions is: "When do I divide my hostas?" Traditionally the answer has been: "In the spring, just as they are coming out of the ground."
Spring may be the easiest time to divide hostas with all their foliage out of the way. And spring is the time of the year that we are all in the mood to clean up the garden and envision the way we want it to look in the summer. It is only natural to want to dig those hosta clumps and spread them out allover the garden, especially when we see how many more divisions there will be in each clump this year than last.
Honestly, spring is not a bad time to divide most hostas, especially those that multiply the fastest and are in the greatest need of being divided. But there are dangers.
So what is the best time? To answer this, let's look at how a hosta grows and see when it might like to be divided.
Hostas sleep all winter and are dormant. They do not make new roots like other perennials do then. In the spring their buds swell and the leaves emerge first. These new leaves emerge, expand and harden off in about three or so weeks. Cool spring soil temperatures may slow or delay this even longer.
As the first leaves harden off and the second flush of leaves begins to appear, the hosta is making new roots from the base of the new shoots. What's important to keep in mind is hostas do not make new roots until the first foliage hardens off.
So what is the damage of dividing hostas in the spring? Namely, timing.
In the spring when the weather is cool and the soil is slow to warm, your newly divided hostas will have large mature leaves and no new roots for weeks. What we call beautiful spring days--those of bright sun, cool breezes and low humidity--are very stressful for new hosta leaves. On these days the desiccation rate is very high and the new divisions with their reduced and possibly damaged root systems dry out very rapidly. If the weather turns suddenly hot for even a day, the hosta leaves will burn. While this damage may not prove permanent, the clumps will certainly reduce in size.
So if you must divide your hostas in the spring, do not over-divide them. Split the clumps in half, or at the most in quarters. Divide only fast growing clumps in spring that can recover quickly. Avoid H. sieboldiana and 'Tokudama' types. Dig them with a fork, not a shovel so as to damage their long roots as little as possible.
Another thing to keep in mind is hosta roots only grow at their tips. If you cut the roots, they rarely branch and will not get any longer. New roots will have to come to take their place.
When then do I prefer to divide my hostas? I like to divide in August or early September, at least 30 days before the first frost date. The conditions then are more favorable for rapid root growth. The soil is warm and the air is more humid than in the spring.
While people prefer the cool, sunny days of spring, hostas grow well in 85-90 F days with high humidity. Also hostas usually put on a little growth spurt in August. Frequently they will throw up a small flush of leaves from the heat of July, especially if there has been rain [or abundant watering]. Many hostas at this time of the year begin to actively grow again after their summer heat dormancy.
Therefore, hostas divided in late summer will make new roots quickly. Many fast-growing hostas will make all new foliage before frost and hold it well into fall. Some may even bloom again.
The only damage in dividing hostas in August is excessive heat or extended drought. Keep newly divided hostas wet. Do not let them dry out for the first two weeks. Removing some of the older, larger leaves or cutting the foliage back at the time of dividing will reduce water loss. Any leaves that suffer burned edges will be taken by frost in a few weeks anyway.
Concerning aesthetics, I would rather have my hosta garden look "divided" as it goes into fall when the hostas are usually past their prime appeal anyway than to see it that way all season long.
Hostas divided in August will come up next spring in their homes with more divisions, better proportioned leaves and established root systems. They will look better too.
So save you heavy hosta dividing for those humid late summer days. It will be tougher on you, but your hostas will thank you in the spring.
Thanks for the inforrmation. You have been looking under the ground better than me! If we must do spring dividing, obviously treating the root tips well and keeping the new clump good and wet are crucial! An addition to your suggestions would be to pot up the fall divisions, and give them an early greenhouse start for spring planting. I have been delighted with how my young ones from last year have gotten a great start in the greenhouse this spring.
Right, Peter. I have a number of hostas in pots, and even outdoors they were the first to leaf out as the soil must have warmed up nicely for them. Maybe next year I'll move them into the cold porch for an extra early start.
BTW, all survived very well in 1 gallon pots right out in the cold and wet and snow, except 'Tattoo' which is no more. It was in a decline last fall, so I am not too surprised, but sad, as I really liked this one.
As of this date I have only 1 more of the many pots to show up but I still await on some 9 older hosta to show up that are in the ground. One is a sum & substance that was very large last year but was the last to show last year (must be a late sleeper). http://davesgarden.com/ej/showimage.php?eid=47586
Very timely as I --- inadvertantly --- weedwhacked down 2 big hosta that had been taken over by wild morning glories... oops, look what's under there. I intended moving them in the spring but I guess I'm going to move them now since the vines take this bed year after year anyway.
When I do... I'm considering planting them in 8"x12" round clay chimney flues for 2 reasons. First, because it might help slow down grubs if the plant is UP in the air. And second cuz I want to add a little height to the bed and see what happens.