By: Teo Spengler
That bushy plant in your garden bearing yellow flowers summer through fall, the one known as St. John’s wort (Hypericum “Hidcote”) may be considered low-maintenance, but it flowers more prolifically if you give it an annual haircut. Read on for information about St. John’s wort pruning, including how and when to cut back St. John’s wort.
St. John’s wort is an undemanding shrub that grows in U.S. Department of Agriculture plant hardiness zones 5 through 9. If your shrub has fewer and fewer flowers every year, you may want to start pruning St. John’s wort.
These are delightful plants to have in your garden, bright and colorful and easy-care. However, an annual pruning is necessary to keep the St. John’s wort nicely shaped and full of summer flowers. It also helps keep the plant in check overall, as it can be prone to getting out of control in some places.
St. John’s wort flowers on new growth. This means that all the blossoms you see in summer bud and bloom on the new wood the plant grows in spring. You must take this timing into account as you decide when to cut back St. John’s wort. You don’t want to reduce summer flowers by cutting off the new growth that will produce them.
In fact, early spring is the time to do St. John’s wort pruning. Cutting back St. John’s wort shrub just before the new growth begins is ideal.
Before you start cutting back St. John’s wort, be sure your shears are clean and sharp. Sterilize them if necessary in a mixture of bleach and water.
If you are wondering how to prune a St. John’s wort shrub, here are some tips:
Cutting back St. John’s wort increases flowering because every place you make a cut will branch into two stems. Each of those stem tips will develop a separate blossom cluster.
Even if your shrub hasn’t flowered for a long time or appears beyond repair, give it a chance. You can prune St. John’s wort very severely – almost all the way to the ground – to rejuvenate it.
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Read more about St. John's Wort
Prepared by Gary L. Wade and James T. Midcap, Extension horticulturists (retired)
Reviewed by Bodie Pennisi
Ornamental plants in the home landscape are pruned for many reasons. Some plants are pruned routinely to maintain a desired size or shape. Others are pruned to promote healthy vigorous growth, flowering or fruiting. Sometimes it is necessary to prune shrubs that overgrow their sites, crowd other plants or limit the view from windows. Plants damaged by insects, diseases or freezing injury may require corrective pruning.
Each plant in the landscape has its own growth habit and a different requirement for pruning. Some shrubs have dwarf growth habits and may never require pruning, while vigorous large-growing shrubs may require frequent pruning.
Anyone can prune, but not everyone prunes properly. Improper pruning, or pruning at the wrong time of the year, can result in mis-shapened plants, reduced flowering or plants that are more likely to be damaged by insects, diseases or winter cold.
This publication provides guidelines for proper pruning that may help assure healthy vigorous plants and lasting landscape beauty. First, we’ll discuss the three basic Ts for successful pruning: tools, technique and timing. Then we’ll examine the pruning requirements of specific ornamental plants in the home landscape.
The perfect choice for brightening lifeless shaded areas. Bright yellow, cup-shaped flowers are an added bonus. Worth growing for beautiful foliage alone. A reliable garden favorite.
A reliable groundcover for any location. Beautiful in shady borders and woodland gardens. Great for erosion control on steep banks and rough slopes.
Slow release feed in spring.
Best in fertile, well-drained soil kept evenly moist. Place in an area protected from cold, drying winds. Prune back early each spring for best display.
Perennials can be planted anytime from spring through fall.
Prepare the garden by breaking up the existing soil (use a hoe, spade, or power tiller) to a depth of 12-16” (30-40cm). Add organic matter such as manure, peat moss or garden compost until the soil is loose and easy to work. Organic ingredients improve drainage, add nutrients, and encourage earthworms and other organisms that help keep soil healthy. Give plants an extra boost by adding a granulated starter fertilizer or all-purpose feed that encourages blooming (for example fertilizers labeled 5-10-5).
Check the plant label for suggested spacing and the mature height of the plant. Position plants so that taller plants are in the center or background of the landscape design and shorter plants in the foreground. To remove the plant from the container, gently brace the base of the plant, tip it sideways and tap the outside of the pot to loosen. Rotate the container and continue to tap, loosening the soil until the plant pulls smoothly from the pot.
Dig the hole up to two times larger than the root ball and deep enough that the plant will be at the same level in the ground as the soil level in the container. Grasping the plant at the top of the root ball, use your finger to lightly rake the roots apart. This is especially important if the roots are dense and have filled up the container. Set the plant in the hole.
Push the soil gently around the roots filling in empty space around the root ball. Firm the soil down around the plant by hand, tamping with the flat side of a small trowel, or even by pressing down on the soil by foot. The soil covering the planting hole should be even with the surrounding soil, or up to one inch higher than the top of the root ball. New plantings should be watered daily for a couple of weeks to get them well established.
Plan ahead, for plants that get tall and require staking or support cages. It’s best to install cages early in the spring, or at planting time, before the foliage gets bushy. Vining plants require vertical space to grow, so provide a trellis, fence, wall or other structure that allows the plant to grow freely and spread.
Finish up with a 2” (5cm) layer of mulch such as shredded bark or compost to make the garden look tidy, reduce weeds, and retain soil moisture.
New plantings should be watered daily for a couple of weeks. After that, depending on the weather and soil type, watering may be adjusted to every two or three days. Clay soils hold moisture longer than sandy soils, so expect to water more frequently in sandy settings.
Different plants have different water needs. Some plants prefer staying on the dry side, others, like to be consistently moist. Refer to the plant label to check a plant’s specific requirements.
Ideally water should only be applied to the root zone - an area roughly 6-12” (15-30cm) from the base of the plant, not the entire plant. A soaker hose is a great investment for keeping plants healthy and reducing water lost through evaporation. Hand watering using a watering wand with a sprinkler head attached is also a good way to control watering. If the garden area is large, and a sprinkler is necessary, try to water in the morning so that plant foliage has time to dry through the day. Moist foliage encourages disease and mold that can weaken or damage plants.
Thoroughly soaking the ground up to 8” (20 cm) every few days is better than watering a little bit daily. Deep watering encourages roots to grow further into the ground resulting in a sturdier plant with more drought tolerance.
To check for soil moisture, use your finger or a small trowel to dig in and examine the soil. If the first 2-4” (5-10cm) of soil is dry, it is time to water.
Incorporate fertilizer into the soil when preparing beds for new plants. Established plants should be fed in early spring, then again halfway through the growing season. Avoid applying fertilizer late in the growing season. This stimulates new growth that can be easily damaged by early frosts.
Fertilizers are available in many forms: granulated, slow-release, liquid feeds, organic or synthetic. Determine which application method is best for the situation and select a product with a nutritional balance designed to encourage blooming (such as 5-10-5).
Reduce the need to fertilize in general by applying a 1-2” (3-5cm) layer of mulch or compost annually. As mulch breaks down it supplies nutrients to the plants and improves the overall soil condition at the same time.
Depending on the flowering habit, snip off faded blooms individually, or wait until the blooming period is over and remove entire flower stalk down to the base of the plant. Removing old flower stems keeps the plant’s energy focused on vigorous growth instead of seed production. Foliage can be pruned freely through the season to remove damaged or discolored leaves, or to maintain plant size.
Do not prune plants after September 1st. Pruning stimulates tender new growth that will damage easily when the first frosts arrive. Perennial plants need time to prepare for winter, or “harden off”. Once plants have died to the ground they are easy to clean up by simply cutting back to about 4” (10cm) above the ground.
The flowering plumes and foliage of ornamental grasses create a beautiful feature in the winter landscape. Leave the entire plant for the winter and cut it back to the ground in early spring, just before new growth starts.
Perennials should be dug up and divided every 3-4 years. This stimulates healthy new growth, encourages future blooming, and provides new plants to expand the garden or share with gardening friends.
Considering that this plant is so invasive, consider growing St. John's wort in a container, where its spreading roots and abundant seeds can be kept in check. This plant is easily established in areas where soil is moist but well-drained and in full sun to part shade. With about 400 Hypericum species, exact cultivation will depend on the variety that you choose, as some species prefer sandy or gravelly soils in sunny areas. According to Missouri Botanical Garden, one species, Hypericum prolificum, commonly called shrubby St. John's wort, likes dry, rocky or sandy soil and is commonly grown as a ground cover. According to the Montana State University Extension, the taproot on a St. John's wort plant can reach 4 or 5 feet deep.
While the plant can produce prolific amounts of seedlings, it can take several years for them to reach reproductive maturity. Seedlings grow slowly and can be outpaced by competing vegetation. Stems die and turn red in the late summer or early fall when the soil dries up or when they experience a frost. Pruning St. John's wort after early spring prevents the plant from flowering that year.
If you are growing St. John's wort in an area where you till, know that small pieces of the roots that get tilled can spread the plant. Once established, it can be difficult to get rid of it without extensive pulling, digging up roots and possibly applying herbicide (for large-scale management). Mowing and burning only encourage these plants to sprout again. Avoid planting it along walkways or where it will get brushed to avoid releasing the unpleasant odor.
Surely spring is the busiest season of the year for the avid perennial gardener. Fortunately, most of us have been cooped up indoors all winter and are anxious to get outside anyhow, and the cool but pleasant spring weather beckons to our gardening spirit!
Is it time yet?
The dead tops of perennials that have been left to stand through the winter are truly not fussy about when you get around to cutting them back. However, heavy and wet clay soil is not a pleasant thing to slog through, and if you have clay soil it might be better to wait until it has a chance to dry out a bit. Treading on wet clay can easily lead to soil compaction — retarding soil drainage and reducing the tiny air spaces that plants require for strong and healthy root growth. Walking within the border too early can also damage the emerging or still-hidden tops of perennials and bulbs. It’s a better idea to wait a bit until your bulbs at least begin to awaken. Some gardeners put down pieces of plywood to walk on, which helps to spread the weight and reduce compaction in any one spot. Another idea is to take advantage of the frozen soil surface first thing in the morning, a sneaky way to get across even a boggy site without causing very much damage.
Which perennials to cut back, and how?
There are basically four types of perennial growth patterns to be aware of when it comes to cutting things back in spring:
1. Evergreen perennials, including many alpines will require no cutting back or only a minimal amount of tidying up. By March or April, if the plant looks green and healthy still, then leave it alone. If just a few leaves are tattered or brown it’s simple enough to trim them back or remove them using sharp scissors or hand pruners. Spring-flowering alpines, for example: Wall Cress (Arabis), Rock Cress (Aubrieta), Basket-of-Gold (Aurinia), Pinks (Dianthus), Candytuft (Iberis), Moss Phlox (Phlox subulata) may suffer a few brown tips over the winter, but no major pruning should be done until after they finish blooming. At that time plants may be trimmed back to half their height using a pair of hedge shears, to encourage a dense and bushy habit.
2. Semi-evergreen perennials sometimes stay completely evergreen in mild winter regions but for many of us they may look so beat up by spring that some of the more tattered leaves need to be removed. Among these are: Bergenia, Coral Bells (Heuchera), Foamy Bells (Heucherella), Foam Flower (Tiarella, Japanese Sedge (Carex), and various ferns.
3. The tall, upright flower stems of Shasta Daisies (Leucanthemum), Coreopsis and Rudbeckia die back in late fall, but these plants keep low ground-hugging rosettes of evergreen leaves that become especially obvious in early spring. Remove the dead upright tops first, then see what the bottom leaves look like. These too may be trimmed a little if they look untidy, removing dead tips with scissors or shears. It’s picky work, so if you just ignore them for a bit the new spring growth will quickly freshen up their appearance.
4. Woody Perennials are better left alone until well into mid-spring before pruning them back. Generally about 6 inches of woody stem is left at the base for the new buds to appear from. Accidentally cutting them right back to the ground will sometimes cause these plants to die. Some examples of woody perennials: Artemisia ‘Huntingdon’ and ‘Powis Castle’, Butterfly Bush (Buddleia), Blue-beard (Caryopteris), Shrubby Wallflower, (Erysimum ‘Bowles’ Mauve’), Fuchsia, St. John’s-wort (Hypericum), Lavender (Lavandula), Tree Mallow (Lavatera), Russian Sage (Perovskia), Cape Fuchsia (Phygelius), Lavender Cotton (Santolina).
True herbaceous perennials are those that die completely back to the ground in winter. Fortunately, this includes the vast majority of common garden perennials. With these, it’s an easy decision — cut everything right back to ground level. A few examples: Peonies, Daylilies, Summer Phlox, Solomon’s Seal, Hosta.
Don’t wait TOO long!
Although cutting back too early can compact the soil badly, waiting until too late in the spring will leave you with a tangled mess of dead plant tops and fresh spring growth. This is very time-consuming to try and deal with, so waiting until late May for example is something to try and avoid also.
What to do with the dead junk?
Unless you suspect or recall a disease problem from the previous season, the dead tops of most perennials can be chopped into small pieces and added to your compost pile. Alternating the dead stuff in layers with green lawn clippings and other “green stuff”, along with the occasional shovel-full of garden soil will have your compost pile off to a great start.
Dispose of any dead tops from diseased plants. Also discard the seedheads of anything you want to discourage from spreading, including both weeds and flowers.
Once things are cut back and the dead tops raked away, overwintered weeds become fairly obvious. Get rid of these in the spring while they’re small and well ahead of when they flower and set seed. Annual weeds (chickweed, garlic mustard) are easy to pull out while the soil is moist. Perennial weeds, particularly deep-rooted ones, may require the help of a fork or dandelion digger to get the entire root system. Discard the roots of perennial weeds in the garbage, not the compost pile.
Some gardeners fertilize every spring, others not quite so often. Newly planted borders are usually good for a couple of years if the soil was prepared well initially. Older gardens often are re-invigorated by a spring feeding, and if you use a mulch of wood chips or bark it is a wise idea to fertilize your perennials every spring. When mulch begins to rot the bacteria responsible will rob the soil of available nitrogen.
There are boxes of fancy perennial food readily available in garden centers, and these are fine if your garden is relatively small. For larger borders it’s a much better deal to buy large bags of all-purpose vegetable garden fertilizer. Look for something with a high middle number (e.g. 5-10-5, 10-15-10) to promote strong stems and lots of flowers. Do NOT be tempted to use lawn fertilizer on your perennials — it is too high in the first number, nitrogen. Also, don’t ever use a “weed and feed” formulation on any part of your garden other than lawn grass.
Whatever product you choose, follow the manufacturer’s rate carefully. Sprinkle fertilizer AROUND your perennials, not directly on top of the clumps. This will help to avoid burning the foliage.
To Mulch, or not to mulch…
The benefits of an organic mulch are many. They add humus-forming organic matter to the soil, improving its structure and eventually supplying food to your perennials. They cover the soil and smother many seeds, reducing the amount of weeding required. The biggest benefit with mulching is that it helps to keep the soil cool and moist during the summer months, thereby reducing watering needs and avoiding drought stress. Mulch should be no thicker than 2—3 inches and should taper off to nothing as it approaches your perennial clumps. In other words, don’t heap mulch all over and smother your plants to death.
Choose a mulch that is good value. This varies from region to region, and includes such things as shredded bark, cocoa beans, rice hulls, commercially bagged or municipal compost, composted steer manure, pine needles and many, many other products. Plain sphagnum peat moss is not a good mulch because it has a tendency to repel water and can blow all over the place.
If you have terrible problems with slugs, consider removing all of your old mulch this spring, leaving the soil exposed to the sun for a few weeks, then replacing with fresh mulch. This will help to eliminate overwintered slugs, snails and their eggs.
Edge your beds
If you didn’t get around to it last fall, spring is a good time to freshen up those bed edges. When you do this, try to follow any invading grass roots and remove them entirely before they invade nearby clumps of perennials.
Moving or dividing perennials in the spring
Spring is an ideal time to move or divide the vast majority of perennials, particularly if you live in a very cold region (Zones 1 to 4). Even the early spring-bloomers can be moved, so long as it gets done before they flower. This might sacrifice a few blooms for the current season, but next year’s display will be especially grand.
Gardeners often ask us when the best season is to move specific perennials, so we have a working “rule of thumb” for timing.
John’s Rule-of-Thumb for when to move or divide perennials
If the plant blooms between early spring and late June, then early fall division/moving is ideal. That being said, you can nearly always get away with doing this in spring, if necessary.
If the plant blooms after late June, then early spring division is ideal.
Exceptions to the rule are: Peonies (move/divide in fall only), Oriental Poppies (move/divide in August), Bearded Iris (move/divide in July through September ideally, or spring as a second choice) and true Lilies (move/divide in mid to late fall).
Of course, you can always break the rules and see what happens. Just remember that if you move or divide a perennial later in the season when it’s big and bushy bushy always cut back the foliage by at least half to prevent serious wilting. This helps to keep the leaf mass in proportion to the reduced number of roots!
A few other tips: fall-blooming ornamental grasses that were left for winter interest need to be cut back before any new growth appears from the base. Some of these, particularly Miscanthus selections, aren’t even going to think about growing until late spring. Gardeners sometimes take advantage of this and leave a few clumps to stand as a lovely contrast to spring-flowering bulbs.
The old leaves of Lenten Roses (Helleborus orientalis or Helleborus hybridus) should be cut right back to the ground in late winter. This allows the emerging new flowers to be seen at their best. Do not trim back most other Hellebores, including Christmas Rose (Helleborus niger).
The old leaves and stems of Barrenwort (Epimedium) should also be trimmed to the ground in late winter.
Hellebores and many other woodland plants may have dropped seed last season that will germinate during the cold days of early spring. Try to be gentle when raking around these, to avoid disturbing any tiny seedlings that might be starting to push through the ground. If you do notice seedlings, wait until early fall to move them to a new location, or even the following spring.
Bearded Iris of all types tend to carry some green leaves through the winter. Carefully pull off any dead leaves in spring and dispose of them, since they can harbour the dreaded Iris borer. If any clumps failed to flower the previous season, you might as well divide them in spring rather than waiting until the traditional summer-dividing time.
Don’t overlook your edible crops while you have pruners in hand. Cut back chive plants after flowering—you can cut these back to stubs and the plant will resprout. Keep an eye on basil. It shouldn’t set flowers this early, but sometimes it tries. Pinch off flower shoots as soon as you see them. Snip back thyme stems after bloom, cutting to just below the lowest flower. Timing on this herb may slide into July. With cilantro, plants start to bolt (flower) as warm weather arrives. You can harvest cilantro seed (the seed of the cilantro plant is called coriander), or let a few plants self-sow and drop seed. You’ll be rewarded with a semi-perennial patch of cilantro. On established tomato plants, remove all leaves and shoots below the first flower cluster. This helps with disease control later in summer.
Edibles to prune in early summer: Chives, cilantro, basil, thyme, tomato.
Too afraid to prune. If you’re just too busy, that's understandable, but if you never prune your clematis because you are afraid you’ll do wrong . . . well, don’t be. If you ignore any vine it will fast become a weed, and clematis are too special to be weeds. Neglected clematis grow tall and bear flowers too high to see, or scramble all around, shade themselves, and bear flowers sparsely. You can do better.
Pruning hard at the wrong time. If you prune a little, it’s okay to prune at the wrong time. If you prune at the right time, it’s okay to prune a lot (“hard”). But if you prune hard at the wrong time, especially if you are shearing off the whole outside of the plant (a bad technique), you won’t see any blooms this year.
If you can’t figure out when to prune because you don’t know when the plant flowers, prune hard just what you need to to keep the size reasonable and let the rest go for a year.