Divide and conquer

04/29/2002
Divide and conquer

As most of us are currently or are about to suffer from a severe bout of planting frenzy, we're probably out in the garden scratching our heads, wondering about where on earth we're going to cram all the new plants we just bought. Or perhaps you are a much calmer and saner gardener who actually has kept one of those oft-recommended garden journals and is now referring to last year's notes to see which of your perennials you want to move or need dividing.

Did you know that a perennial should be divided whenever you move it? A plant that is hacked at least in half will put down new roots and grow much more vigorously than one that is moved intact. This is a key concept to understand: Division reinvigorates perennials. That's why a clump of iris or anything else that begins to die out in the middle, as in the main photo above, is a prime candidate for the "divide and conquer" maxim of perennial gardening.

Aggressive growers such as beebalms (Monarda spp.) also need frequent division to keep them in bounds. Old diehards like daylilies and hosta also profit from division every 3 years or so. Anytime a clump starts to look woody and bare in the middle, or otherwise seems to be diminishing in vigor, is your cue to perform rather crude surgery on your victim.

Dividing perennials is easy to do; the most difficult part of the whole process is usually deciding what to do with all the resulting divisions. You can't believe how many offspring a single clump can generate! Resist the temptation to replant them all, unless you really need them. This is the time to be generous to your gardening friends--or enemies--depending on the nature of the plant you're dividing.



The first step is to water your victim thoroughly. The reason is that you're about to traumatize the plant by causing it to lose a lot of roots. You want to have the plant as turgid and hydrated as possible before you proceed. Ideally, water the evening before you plan to divide.

If the top growth of the plant is already quite tall (more than 6 to 10 inches), cut it back by one-third to one-half. This may seem brutal, but the plant will recover much more quickly if you do it. And many perennials will put forth more flowers later on after this pruning. That said, you will notice in the photos that I did not cut back this iris. The reason is that it will bloom soon, and also, that I can get away with not cutting it back because I am gardening in the extremely cool, humid climate of Normandy. The hotter and drier your locale, the more important to cut back before dividing.






Next, dig up the perennial. A plant with bulbous roots such as this iris is easy to dig up in pieces. But most perennials are fibrous-rooted and will need to be dug up in a big clump. Really monstrous ones can actually be cut into pieces while still in the ground for easier handling. Just take a sharp space and cut the clump in to quarters before digging it out.



Separate the clump into pieces. How you do this will again depend on the nature of the root system. Extremely tough, fibrous clumps will need a solid tromp on a sharp space to cut them. This iris, on the other hand, separated easily in my hands. A heavy knife is a good tool to use for dividing most perennials.




Your divisions should have at least two to three "eyes" or growing points. Larger divisions are okay; it all depends on how many plants you want to end up with.
Try to cut between the eyes. If you can't see where they are, use a jet of water from the hose to wash away enough of the soil so you can see what you're doing. Make sure to discard all woody or dead portions of the plant. Take divisions only from vigorous parts. Water your newly separated divisions and keep them shaded and moist while you prepare their new home.



If I have one hard-and-fast gardening rule, it's never to plant anything without amending the soil. Or re-amending it. Take this opportunity to refresh the soil for your new divisions by working in plenty of compost. Here, I'm using an angled Provençal shovel, which is just perfect for scooping up and flinging compost and mulch, to load the area with composted horse manure. Bone meal is a good addition as well, as it will stimulate your new transplants to grow new roots quickly.



Now, mix all those rich amendments thoroughly into the surrounding soil. As always, the appropriate tools make the job much easier. In the photo below, I am using an essadonnet, a traditional Provençal tool that is shaped like a very long-bladed hoe. This is just the ticket to bite into clumps of soil and compost and chew them up into a fine and even mixture.



When you've done your job well, you'll have real "pay dirt"--rich, finely textured soil that is easy to plunge a garden fork--or even your hands--into. To dig the holes for new plants, I like to use a fork. It doesn't leave a slick-sided hole like a shovel can in wet or heavier soils.
When your soil is well-worked, planting your divisions takes just a matter of seconds. Space your plants adequately to allow them room to grow.



Water your new plants in thoroughly and you're good to go! If the weather is hot, you may provide some temporary shade for your new transplants for the first few days. Also, make sure to water them often until they get a toehold.

Spring is an excellent time to divide most of your perennials. The only exceptions are the early-flowering ones which are currently in bloom. Optimally, wait until early fall to divide those.

The other only exception is tap-rooted perennials such as gasplant (Dictamnus albus), butterflyweed (Asclepias spp.), and false indigos (Baptisia spp.). These plants are best left in place for the duration of their lives. If you must relocate them, handle them as if they are shrubs, digging a large rootball and wrapping it carefully to keep the soil from breaking off the coarse roots. Cut back the topgrowth by half, water often, and provide shade for the first few days to cushion the shock.

But in all other cases, the rule is divide and conquer!

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Products of Interest:
Provenandccedil;al garden fork
Provençal essadonet (garden cultivator)

'Paris' garden fork