Herbaceous perennials are those gorgeous plants you fall in love with in garden magazines. They are versatile with fabulous flowers and beautiful form. Many fear their beauty must be too complicated to try, but in reality they are easy and don’t require a lot of maintenance. Here is our advice on how to look after them like a pro!
The official classification for a herbaceous perennial is a plant that lives for more than two years, this is then broken into two groups; woody perennials and herbaceous perennials.
Woody perennials are those that are above ground year round, with ‘woody growth’, or firm stems. Examples are hydrangeas and roses. Woody perennials may be evergreen, which are in foliage all year, or semi evergreen, which should be selectively pruned, usually in autumn or winter to promote healthy growth.
Herbaceous perennials are soft stemmed, or non-woody. They die back to ground level each year for a dormancy, or rest period. Examples include hostas and aquilegias.
They are brilliant plants because they can stay in the ground and get better and better year after year. Once established, the root system needs minimal maintenance (water, fertiliser and occasional pruning). They add excitement, colour and variety to the garden as well as mark the changes in seasons. Oh, I shouldn’t forget to mention they are excellent value for money. You can time your show so you have a cacophony of colour and form, or draw it out over a long season, or with careful planning both!
There is a wide range of herbaceous perennials that grow in all sorts of different garden situations, from full sun to full shade, boggy to dry soils and everything in between, so pick the plant that is right for you.
HOW DO I GROW HERBACEOUS PERENNIALS?
These simple techniques apply to a huge range of plants. Once you have learned and applied them to one, you can expand your collection and will look like a gardening professional!
Before planting, soak the pot in a bucket, and, if you have it handy, add a seaweed nutrient for a bit of extra oomph. You will know the root ball is saturated once the bubbles stop rising to the top.
If your plant has come through mail order, or sat in the hot car on the way home from a nursery, think of how you feel after a long haul flight, you need a good cup of tea and
a biscuit before you are ready to face the world again, well it is the same for plants!
To prepare your soil you should first remove any weeds or grass that may be growing there. Once this is done, dig into your soil to around the depth of a spade. As you dig through the soil, add a well rotted manure or compost to help to enrich the nutrient content and improve drainage. This should be done at the rate of about a handful for each square metre. Once this is done water it in gently, then you are ready for planting.
You should allow your plants their full space requirement from the start. This will leave you with an initial bare spot that will be filled relatively quickly depending on the variety you have planted. Once spring starts you will be surprised at how quickly they establish. If the bare spot nags at you, put some annuals in to fill the gap, they are cheap and cheerful, and by the time they begin to fade the herbaceous perennials will be up and growing.
To work out the amount of space a plant requires to grow, check the plant details for the width. For example if a plant grows 1m wide, space it so the neighbouring plant is 90cm away, this allows for a slight overlap which will fill the space and reduce weed growth. An easy way to do this is to lay your pots where you intend to plant them and use a measuring tape to determine their location.
See our article on how to plant out and establish new pots here for all you need to know. ADD HYPERLINK I CAN’T AS THE SITE DOESN’T EXIST YET. In short, dig the hole wider than it needs to be, wet it, then place your plant so it sits where the roots meet the stem at soil level, refill the hole and firm the soil.
When planting bare rooted perennials you follow similar guidelines; dig a hole deep enough to cover the roots, and allow the growing tip to sit at the soil surface. Once you have done this firm the surrounding soil and water in well.
The best thing you can do for your perennials is to keep them well watered during their establishment, even if they are listed as dry tolerant. The soil should be moist but not boggy. When you water it is best applied to the soil rather than the foliage, this minimises water loss through evaporation and reduces the threat of fungal disease on the foliage. The best watering methods are drip irrigation or hose. Once established plants will require less water and the amount depends on your chosen plants.
Herbaceous perennials grow very rapidly from spring onwards. In many cases they go from nothing to a full flowering plant in a matter of weeks. To facilitate this growth they require lots of food.
As a general rule, anything is better than nothing, so if you see an all purpose fertiliser on special grab it! Grow Better All Purpose Plant Food is a nice all rounder as is Osmocote. For best results, add the fertiliser as the plants begin to grow in spring, then again when they are flowering in summer. Read the label on the packet for the correct dosage.
Adding a layer of organic mulch in summer will protect the plants root system from overheating and also help to maintain moisture in the soil, so you need to water less. As the mulch decomposes it will add extra humus to the soil improving drainage and adding nutrients.
Mulching in winter helps the plant better cope with fluctuating soil temperatures and helps to protect the crown from frost.
If you have a choice, it is always easiest to avoid staking by growing your plants in a protected area.
Plants with big flowers such as dahlias or tall growth such as delphiniums may require staking. It is best to stake your plants at the time of planting, or in early spring before any major growth could be damaged. Make sure your stake is secured well into the ground so it will not topple over. As they grow up, loosely tie your plant (allow some movement) using a figure eight between the stem and the support. Match your choice of support to the plant, some are heavier than others. It is best to use the shortest stake possible so the plant will grow up and hide it.
For some perennials, removing dead or dying flowers you will encourage more blooms, this takes just a few minutes and is well worth the time. This is true for plants such as nepeta, Marguerite daisies, agastaches and dahlias. Some herbaceous perennials such as aquilegias will self seed, only deadhead these plants if you want to stop them producing offspring.
Flowers are produced to attract pollinators so that plants can reproduce through viable seed.If you leave the flower heads on, the plant has performed its function and will stop putting its energy into producing more growth and flowers. If you remove the flowers before the seed is formed, then, in most cases the plant will continue to flower.
Herbaceous perennials such as delphiniums and foxgloves can bloom twice in one season. Simply cut the flower stem back to the ground, allowing the foliage to persist, and add some fertiliser and they will rebloom in autumn.
Over time perennials may become overcrowded, when this happens it is a good idea to dig and divide them. You can share the spoils with family and friends, or replant them in your own garden. Digging and dividing perennials is easy to do, the method depends on the type of perennial you are growing, but basically involves lifting and splitting the plant then replanting every two to five years. Keep an eye out for our up coming article on the nitty gritty of the how to coming soon.
Healthy plants are unlikely to be affected by pests and diseases, so if you water well, have good air circulation, remove any weeds and keep up regular applications of fertiliser you are unlikely to have a problem.
SLUGS AND SNAILS
When establishing plants it is always a good idea to protect the young growth from slugs and snails. There are all sorts of ways to do this from squashing them with your garden boot to placing pots of beer out for them to fall into. While there are poisons out there it is always a good idea to explore other more natural options first.
Aphids are spread by wind and infested plant materials, they are most common in warm weather. Aphids multiply quickly so check plants regularly. Aphids suck the sap from plants, they congregate on stems, flower buds and the underside of leaves. Aphids excrete honeydew, transmit virus, cause galls and bud failure on plants.
To remove aphids first try squirting them off with a strong hose or use your hands to squash them. Natural predators include ladybirds and parasitic wasps. If the infestation is large, you could try a household soap solution remedy, or a relatively eco friendly insecticide such as neem oil.
MILDEW AND FUNGAL DISEASES
If ventilation is poor mildew or fungal diseases may occur. This shows as spots or powdery discolouration on leaves, it can also cause distorted buds and foliage. Affected leaves should be removed and discarded in the bin (not the compost). You can avoid the problem by ensuring there is a good amount of air flow around your plants (they are not too overcrowded) and by only watering on the roots rather than the leaves. If the problem persists you might like to use a fungicide, there are lots of organic recipes to try before you need to get out the chemicals.
Cutting your perennials right back once they have finished flowering will keep them happy, healthy and looking good, it is easy to do and doesn’t take much time. There are many perennials that can keep their senescent foliage for winter interest, such as ornamental grasses but, for some it is off with their heads!
Often times as herbaceous perennials go into dormancy their foliage can become unsightly or collapse. Removing these stems will improve your garden appearance, and it has the added benefit of keeping the growing crown healthy.
It can improve flower production by revitalising the plant. It improves air flow as they plant will not be congested by dead or dying branches. Pruning promotes compact, well branched growth as plants are shooting from healthy stock.
PRUNING HERBACEOUS PERENNIALS
Herbaceous perennials naturally die back to the level of the soil in winter and so can be cut back in autumn or early spring. The new growth usually shoots in spring. You don’t need any special skills to prune a perennial, just a good steady hand with a sharp cutting tool and it will all be done and dusted in no time.
In autumn or winter cut the dead or dying stems right back to the crown of the plant. Leave any new growth and cut off the old stuff off just above. Some perennials such as peonies grow from an underground crown so can be cut right back to soil level. Other perennials such as salvias and sedum will already have new growth from the crown above the soil so don’t need to be cut back as hard. The refuse can be tossed on the compost heap. Once you have finished pruning add a layer of mulch around the crown.
Spring pruning follows the same principals. If you allow some of your perennials such as grasses to persist through autumn and winter it will help to maintain structure in the garden. Be careful when you are cutting back to avoid any new growth that is emerging. In some cases, ornamental grasses for instance, you will simply be able to pull out the dead stems to avoid damaging the new growth. Add some fertiliser when you are done.
Brunnera leaves become unsightly in cool weather as they turn brown and black. Similar to many herbaceous perennials they canbe easily cut back to just above ground level with secateurs.
This is an optional extra mid season prune. Known as the Chelsea Chop (because in the northern hemisphere it is done in May, in Australia November is the ideal time) this method of pruning will reduce leggy growth so plants are unlikely to require staking. Use pruning shears or secateurs cut the foliage back by one third to a half in November. This will result in more side shoots, therefore more flowers and a later flowering time. Plants that benefit from this type of pruning include echinacea, rudbeckia and phlox.
PRUNING WOODY PERENNIALS
Prune woody perennials so the old stems are left to protect the growing crown. Woody perennials are divided into 12 different pruning group categories. It is important you know which category yours falls into otherwise you may prune off flowering buds. This type of pruning requires detailed explanation that can be found in our upcoming pruning blog.
So there it is, all you need to know and more on how to grow spectacular perennials, we hope this inspires you to have some fun with them!