It's tough to talk about this tool as a “pruning” tool because hedge shears are not used for the type of work that we typically think of as pruning. In the right very few circumstances, hedge shears are a must-have or a convenience. But when used in the wrong situations and the wrong hands, the things are a tool of evil, especially the motorized gas- and electric-powered varieties.
What Are Hedge Shears?
Hand-operated hedge shears, more than any other gardening tool, look like giant scissors. They have long, straight blades typically somewhat under a foot long, sometimes wavy-edged to hold stems in place as they cut (but which are harder to sharpen.)
With such long blades, hedge shears are designed to cut a much larger area with each stroke than any other pruning tool (unless you consider a machete a pruning tool). For this reason, and since they are straight, they create long, straight edges on your plant as they cut. As you can imagine, this is not the natural shape of any plant, and not right for most plant care in your garden.
The fact is, you can probably get by without owning hedge shears. You only need them if you have a formal hedge to maintain, and they’ll be very handy for fall and spring cutting-back if you have a lot of perennials and ornamental grasses. For other jobs where you change the shape of the plant by managing its woody framework, pruners, loppers, and saws are the right tools.
The Only Times to Use Hedge Shears
There are just three situations in which you need to use hedge shears. Note that in all of these cases, hedge shears are used to cut through the soft, non-woody stems of plants. Hedge shears absolutely cannot cleanly or efficiently cut through wood, even thin wood. Using shears to do this not only causes unhealthy cuts to the plant but damage to the blades of the shears.
- Maintaining a Formal Hedge. This is really what these things were designed for, which is unsurprising given the name “hedge shears.” Shears are designed to quickly let you impose a geometric edge on the soft new growth of a plant (most classically, boxwood), cutting a lot at once in a straight line. The only time you want to do this to a plant is in formal hedging and topiary, where stylized, artificial looks are desired. But this only works for a few species that can be treated like this. For the vast majority of shrubs, where the goal of pruning is to develop a managed naturalistic appearance, the straight lines made by hedge shears are completely inappropriate.
- Cutting Back Perennials. Depending on your plants and your aesthetic style, you’ll need to cut perennials back to their crowns in fall or early spring. Since these cuts can be made imprecisely and just require cutting a bunch of soft, dead stem tissue at a time, shears are great for this. They work well with plants that are completely soft such as catmint, hostas, lilyturf, and most other perennials and ornamental grasses.
Shears do not work well with cane plants that need thinning, such as raspberries—for these use a woodsman’s pal or another machete-type tool. Shears can also have problems with semi-woody perennials that develop hard tissue at their stem bases if you try to cut too low. Some mints fall into this category.
- Yearly Taming or Deadheading of extremely prolific, soft plants, that produce so much growth that hand-pruning would take too long. Some mature non-woody clematis and vines are this way, and will grow fast enough to hide the unnatural cuts; some say miniature roses fall in the same category. Some prolifically small-flowering plants, such as santolina, tickseed, and lavender can be deadheaded well with well-aimed shears.
General Use of Shears
Being large scissors, shears are used just as you naturally want to: snip away! How accurate you need to be will depend on which of the above tasks you are doing. One major difference between shears and other pruning tools is that you do not need to aim to cut above the nodes of the plant, but rather you snip to create lines: near the ground for perennial cutback, and in special patterns in hedging and topiary.