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FERTILIZING
A well-established perennial garden needs no additional fertilizing if it is mulched with compost (homemade) or manure. Keep in mind, you are feeding the soil as well as the plants. A soil with a loose texture and lots of organic matter will produce a better garden than heavy applica-tions of commercial fertilizers. The one exception to this rule: spring bulbs should be fed in early spring, when the narcissus bulbs are up about one and a half to two inches tall; this will help them produce a good bulb for the following year.
New plants can be fertilized at planting time. A small amount of a transplanter, an all-purpose plant food, or a similar organic plant food mixed in the planting hole will increase survivability and promote a good “take” that fi rst year.
General overall fertilizing of perennials should be with an all-purpose type of granular fertilizer, organic or not. You can also use vegetable fertilizer, which is usually a similar balance of N-P-K (nitrogen, phos-phorus, potassium) like 5-10-10 or 4-8-8. This should be done in early spring.
Slow-release fertilizers can be used, but the expensive encapsulated ones need to be incorporated into the soil to work best. If granular or encapsulated products are used on the surface, they can fl ush all at once in hot weather;
early, cooler-season applications are better.
WATERING
If you don’t want to stake your perennials, don’t overhead water. When fl owers get laden with water and weighed High tide in the garden with waves of summer color rolling down the slope. The top wave has Rudbeckia
lacin-iata ‘Herbstsonne’, Delphinium elatum, and Miscanthus sinensis ‘Zebrinus’. In the central billows are R. fulgida var. sullivantii ‘Goldsturm’, Patrinia scabiosifolia ‘Nagoya’, and Agapanthus ‘Prolifi c Blue’. In the foreground are Phygelius ×rectus ‘Salmon Leap’, Hypericum ×inodorum ‘Elstead’ in fruit and a variegated hypericum, and Berberis thunbergii f. atropurpurea ‘Golden Ring’.
Maintenance Guidelines
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26 Perennials: A Gardener’s Reference
down, plants fl op. Install a leaky pipe system like Aqua-pore or Netafi n, and keep water off the foliage and fl owers.
This will also reduce disease.
A good heavy application, once a week, of an inch of water is usually suffi cient, except for newly planted areas, where watering individual plants is still necessary until well established. Perennials do very well with a heavily water-retentive soil under the more prepared humus-rich soil in your planting beds.
If you can, you should always water in the morning, so your foliage can go through the night as dry as possible.
A loose mulch that acts as insulation will conserve water and keep your soil moist and reduce water loss by evapo-ration from the soil surface through capillary action.
THE DRY-GARDEN, DROUGHT-TOLERANT MYTH Some perennials can take less watering once established but will need to be watered or watched now and then (every seven to ten days). The bulk of good garden plants come from areas that receive summer rain—the United States east of the Mississippi, wetter areas of Europe, China, and New Zealand. Nothing looks worse than a perennial border in England in a severe drought year; they are very strict on watering, and most gardens have little supplemental water and rarely an irrigation system. Our climate is unusual in that we can have very dry (but not hot) summers and very wet falls, winters, and springs.
In a dry year, let your lawn fend for itself, and save your water for the perennials and shrubs. Lawns usually come back but a bone-dry delphinium is a dead delphinium.
Some plants that can be grown in drier soil once established are adenophora, allium, anaphalis, artemisia, camassia, centranthus, delosperma, dierama, euphorbia (most of them), ferula (but it will be shorter), glau-cium, kniphofi a (fl eshy roots and deep rooting), Papaver atlanticum, P. orientale (usually goes summer dormant), perovskia, romneya, salvia (some), sedum, tellima, tolmiea, tradescantia (fl eshy roots and a large root system), Viola adunca, V. labradorica, and vancouveria.
WET FEET
A few perennials can take wet feet most of the time, although the winter water level cannot rise above the level of the crown. These plants can be used at the edge of a stream, pond, or lake if planted above the high-water mark. If they wish to be closer, most will grow in that direction. Iris ensata, I. laevigata, and I. pseudacorus will grow in water. See the A-to-Z for specifi cs about these
plants (“planting” will tell how far above the high-water mark they should be): acorus, darmera, gunnera, hout-tuynia, Primula beesiana, P. ×bulleesiana, P. bulleyana, P. japonica, trollius.
PINCHING
This is the term for the practice of removing the tip growth on each stem of an herbaceous plant. The purpose is to keep the plant more compact so that staking will not be required and so that the plant will “fi t” its allotted space.
This practice is not a universal one—some plants respond well, others don’t, and it is important to know who likes what before pinching back or pinching out. Examples of a positive outcome would be chrysanthemum, aster, and boltonia; plants that do not respond well to this treatment are sedum, Campanula lactifl ora, and Phlox paniculata.
What is less than satisfactory is the effect on the fl ower heads themselves, which are usually much smaller than they would be if left alone. Pinching changes the character of the infl orescences. Often a short, cool summer does not give enough time for a good-sized fl ower head to form.
STAKING
This is the process of propping up plants that have a tendency to fall over, fl op, or splay. Plants should be staked in early spring as they emerge from dormancy for two reasons: you can get into the garden to do it; and it is much better to do it in advance—if you wait until the need is obvious, it is usually too late to do it well. Staking should be as unobtrusive as possible once the plants have grown up into the supports.
With many herbaceous plants, support is lent by what we call pea sticks. These are bits of brushy wood with sturdy, thin twigs—hazelnut, birch, or maple twigs, for example—with their single, broader stem end forced into the ground around the plants they’re meant to support.
Taller plants like delphinium will need straighter, taller supports and some tying-in. Paeonia and Helleborus argutifolius are examples of plants that can benefi t from those circular wire hoops (which you’ve put in early, for them to grow up through).
GROOMING
Herbaceous plants need grooming throughout the year.
Many have their fl ower stems completely removed after fl owering. In some cases, this will result in rebloom, depending on the type of plant. Some plants simply
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have the spent fl owers removed to the next leaf or pair of leaves, and this stimulates further fl ower production in response to this removal of any possible seed produc-tion. If you are interested in saving seed, you can select a couple of stems that look really good to leave for seed production. If you like the appearance of the seedheads, you can leave them until you want to remove them; the latest they should remain is into the following spring, when growth recommences.
Other grooming, carried out as needed, involves removing dying, damaged, or diseased foliage as it occurs.
Daylilies often need their bad leaves removed—in this case, it’s leaf by leaf. There are more serious kinds of grooming as well. For example, Alchemilla mollis is groomed (cut) to the ground after all the fl owers turn brown. All the leaves and fl ower stems are removed. The plant will releaf within a couple of weeks with a heavy watering; the result is a handsome plant for the rest of the season. This process
Scrim plants, the delicious Helianthus salicifolius (willow-leaved sunfl ower) and Verbena bonariensis, fronting a mass of Cortaderia selloana ‘Sunstripe’ backed by Sambucus nigra ‘Guincho Purple’ and a bit of Arundo donax (top right).
also reduces self-sowing. Be sure to water well any plant you subject to this extreme treatment.
Many plants have the occasional bad-looking leaf or two; just remove as needed. The plants will usually show you what to do.
DEADHEADING
Deadheading is a lot like grooming but specifi c to the fl ower heads. Again it is important to know whether and when to do this. For example, most peonies benefi t from having their spent fl owers removed—they look better, and it reduces the chance of disease forming on the old petals and jumping to the leaves. A few peonies, however, have beautiful seedheads, and some can be seed-grown.
You can either admire for a while, before deadheading, or leave any species to form seeds (hybrid peonies rarely form seed).
Maintenance Guidelines
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Delphiniums are often deadheaded to the leaves below the fl ower structure, but we now know that the plants will be more robust if you forgo the funny little second fl owers and just cut them to the ground after fl owering.
You may in fact get a great reboom in late summer or fall.
Do not do this to young plants.
Never deadhead by simply removing the fl owers and leaving the stems. This looks dreadful, and as the fl ower stems die back, the plant will either look even worse or may become diseased along the stem (pansies, for example, are prone to this).
CUTTING BACK
A specifi c form of grooming, this is the process of taking plants nearly to the ground. There are several occasions where this might be the appropriate course of action.
1) Many herbaceous plants are cut back during the fall and winter months. Usually this is based on both the appearance of the plants and the gardener’s need for access. Especially following the fi rst serious frost, a lot of plants begin to go into dormancy, and the upper growth deteriorates—sometimes overnight. Some plants will have a basal structure that is visible and green below the decaying stems. If so, cut only to this new growth, leaving an inch or two of old stem to mark the place where the plant is and to protect it from your big feet. Other plants will have nothing visible except their dead stems, and these should also be cut down to one to two inches, for the same reasons.
2) Many plants are dormant at times other than autumn.
Spring bloomers can go dormant by summer; some don’t leave a trace, and others need a bit of cutting back. It will be obvious.
3) Some perennials should not be cut back until spring.
Maybe they’re valuable for interest in the winter garden, or because they protect their crowns during the cold months. Another reason you might wait is to provide food and shelter to the other garden dwellers.
Plants to leave up might include helianthus, foenic-ulum, rudbeckia, and phytolacca.
SHEARING
Shearing is for lambs and lavender. This is not an appro-priate term for the care of most herbaceous plants since we do not use shears on them.
WINTER CARE
Put your garden to bed for the long dormancy of winter.
It is best to let your perennials go fully dormant before cutting them back for winter. Allow the iris to turn yellow and nut-brown, and let your peonies go through their nice reds, oranges, and golds. Cut lilies back after all leaves have turned; your cut should be at a sharp angle so some water will run off. Do not compost peonies and lily leaves—too much disease present.
Plants with a visible winter crown like sedums and asters can be cut close and do not get covered with mulch.
Hostas and daylilies can be cut quite close and covered with mulch. If you need to walk in your beds, leave a few stems up high enough so your plants show above the mulch. Try not to step on the crown of any plant.
Clean up your crowns, and check for slugs and weeds in the center of the clump or just at the edge, hiding under foliage. Don’t worry about accidentally removing some soil or mulch at this point, as this is the best time to put fresh mulch on. Plant your bulbs as you clean up so they can have a good mulch too. Put the waste in your compost, and layer with leaves, soil, and chopped green stems.
Many perennials and grasses can be left for winter interest, but this can be a bit messy. You’ll need to decide what is best for your garden.
1) Perennials that have good fall color but no strong, upright stems (hostas and daylilies) should be cleaned up fi rst and checked for slugs, which can still do a lot of damage throughout the winter.
2) If protected, leave the plant up for the chance of hoar-frost and a stunningly beautiful, if fl eeting effect.
3) If windy, we recommend cutting grasses down just before they begin to fall apart.
4) Woody and semi-woody fl ower stems can be left until they break off easily (astilbe, eryngium, rudbeckia).
This is the time to put limestone chips (marble chips) on the crowns of your hellebores and peonies. These chips are normally used for terrazzo fl oors. They slough molecules constantly and will change the pH around and on the crown they cover, but not the overall pH of the soil. This slightly less acid “mulch” will interfere with the overwintering of the botrytis organisms, so the plants don’t pick up this disease when emerging in the spring.
This technique also makes the crowns easy to locate when mulching as both of these plants should not be mulched over.
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WINTER MULCH
In addition to normal mulching, some plants will benefi t from specifi c winter mulches. If you are planning to plant a new area in spring that is currently either in lawn or weeds, you can reduce your work by mowing or weeding the area (weedwhacker, blow torch, goats) and then covering it with thick piles of newspaper, overlapping for complete coverage. Then apply ten to twelve inches of straw, hay, manure, or leaves. If using leaves, top-dress with compost or something heavy enough to keep the leaves in place. By spring you should be able to turn in the mulch and plant without having to remove the lawn, as it will be dead and the paper will have rotted away.
Another winter mulch would be the application of fi r boughs or other coniferous blow-downs or pruning as an insulation over tender plants; newly planted and not-established plants; plants that might frost-heave in your garden; and plants you didn’t get planted (still in their containers). This blanket of covering keeps things under
In this single color scheme, Phlox paniculata ‘Bright Eyes’ is framed by a mass of centaureas in the foreground and backed by Viburnum carlesii and Macleaya cordata.
it from freezing. Do not use hemlock, as it will just drop its needles and you’ll have a mess to clean up. We even cut up our holiday trees (afterward) and use those boughs in the garden.
Some plants benefi t from a mulch of their own big leaves in winter for cold protection, for instance, Gunnera manicata and hedychium. Cut off leaves in fall and cover the plants for the winter; remove them in spring, as the buds swell and weather warms up.
Much of the mulching material for winter can be incorporated in the soil if suffi ciently decomposed, or it can be chopped up and added to the compost heap come spring. The exception would be the conifer branches, which should be disposed of in another manner.
CUT FLOWERS
We all know that the best time to cut fl owers for arranging is early in the morning. That said, do it when you can, and Maintenance Guidelines
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avoid the hottest part of the day. The further you can get from noon, in either direction, the better.
Flowers should immediately be placed in water as you cut them. This is not always practical but get them in water as soon as possible. The best fl orists condition cut fl owers overnight by immersing them up to their necks, with the fl owers above the tepid water; they arrange the stems the following day. If any cut stem spends time between being cut and being in water, recut the stems before conditioning.
Some plants have milky or liquid saps that run out the cut end. These (poppies, macleaya, euphorbia) and those plants with hairy stems should be singed with a match or other fl ame before going into water. If you do not do this, they won’t be able to draw water up and will go limp in the vase.
Hellebores are a special case. Cut them, then take a pin or the like and poke holes up and down the stems. Fill a sink or tub with water, and fl oat the hellebores in it overnight. Arrange the next day, and you’ll have two weeks of fl owers.
Plants with woody stems should be cut at an angle, split at the bottom with your pruners, and hammered (smashed) at the base before putting in water.
There are some good fl oral products to add to the water that will prolong the vase life of fl owers. Change the water every few days to help keep the fl owers as long as possible.
PROPAGATION
As gardeners most of us are involved in some method of plant propagation. If you are seriously interested in collecting seed or taking cuttings, we recommend that you do further reading on these subjects; there are good books that cover this in great detail. Division, however, is a tech-nique that benefi ts many plants, whether you are planning on having additional plants or simply dividing a congested one, so your plant will bloom better and look better. We have noted the best time to divide, if appropriate, for each individual plant throughout the A-to-Z. The standard rules are these: plants that bloom in spring and early summer are divided in autumn; plants that bloom in late summer and autumn are divided in the spring. But some plants, such as astrantia or plantago, can be divided in spring or autumn without any noticeable set back. Pulmonaria can be divided in early spring at fl owering time.
Some of the perennials that really benefi t from division also have features that make it a challenge. Iris sibirica
forms very large, dense clumps; a sharp axe may be the only way to split it up. Others are tap-rooted (aquilegia, eryngium), and another means of propagation may be the
forms very large, dense clumps; a sharp axe may be the only way to split it up. Others are tap-rooted (aquilegia, eryngium), and another means of propagation may be the