Updated/Fact-Chacked on June 14, 2023 by Gareth James
I have recently created a new border in my front garden, removing a patch of grass to create a new mini bed. As the bed sits directly under my front window, I want to be able to see flower heads this summer from a seated couch position – this means they have to be at least 70cm tall.
I have spent hours pouring over my RHS plant encyclopedia (highly recommended book) to find tall flowering plants I like; this article was written from my shortlist. Some of these plants will also be used in the back of my main border if they fit my ‘long flowering season‘ criteria.
When choosing tall border plants, you are generally limited to perennials – plants that will give you flowers every year for at least two years and often longer. However, you can find a few annuals that add vertical interest, like Cosmos bipinnatus ‘Versailles Dark Rose’ at 1.5 metres high and sunflowers.
In this article, I have focused on tall flowering plants for the back of borders and have excluded all shrubs. I am writing a new article around tall evergreen border plants as most of the plants below will not give you winter interest.
Things to consider when growing tall perennials
1) Is the plant a herbaceous perennial? This means the plant will die back in winter, leaving bare patches in your border. If you want some winter interest, consider plants that leave seed heads like rudbeckia or echinacea or choose from the small variety of evergreen perennials. Seed heads will also provide food for small birds in the winter months.
2) Consider a mix of plants with varying flowering times, so you have colour from May to the first frost in October/November.
3) Plant in groups that require similar growing conditions (Soil PH, position) to get the best results.
4) When thinking about a tall plant’s height, don’t overlook the width it will spread. Some plants will spread widely and block out light for other plants.
5) Consider the plant’s foliage as well as flower colour to create a mixture of textures and shapes.
6) Some of these tall flowering plants may require staking, depending on their location. Even though I staked my sunflowers last year, the North East winds killed them off.
7) Try to choose bee-friendly and native plants as much as possible.
Sunflowers are easy to grow from seed, simply plant in pots in March-April and plant out when the risk of frost is minimal. Sunflowers are great for kids to grow as they can give impressive height if you have the right variety. You can also get varieties with multiple flower heads.
One of the tallest sunflowers is Helianthus annuus ‘Russian Giant’, which can reach 2.5M. If you are looking for a tall perennial sunflower, then Helianthus ‘Lemon Queen’ is your flower.
Thalictrum (meadow rues)
Height: 1 -2 M depending on the variety
Flowers: July to September
Some thalictrum can grow to over 2 m tall, perfect for a perennial border. You can get small thalictrum, so make sure you buy a tall variety like thalictrum flavum, thalictrum splendide or thalictrum aquilegiifolium.
Thalictrum is relatively easy to grow in moist soil and does well in sunny or partial-shade conditions.
Flowers: June – September
Delphinium is generally hardy-tall perennial that do well at the back of a sunny border. They need well-drained soil and protection from slugs and snails during the spring.
With a height of 2m, you may need to stake your delphinium if not in a secluded area. I’m currently growing them from seed and planning how to protect them from the North East winds, all my tall grasses have been destroyed from the recent storms.
Note that plants like delphinium tend not to reach their maximum height in the first year – my white delphinium above was only half the size last year. The purple variety in my front border has only reached 60cm this year, probably due to poorer soil conditions.
Delphinium comes in hundreds of varieties, so choose one to compliment your border colour scheme. Here are a few worth considering:
Magic Fountains – White
Elatum Blueberry Pie – Blue
Elatum Bollero – Lilac
Elatum Cha Cha – Cream
New Millenium Pink Punch – pink
Elatum Sungleam – yellow
Flowers: June to October
Agapanthus has amazing-looking large flowering heads that will tower over all your middle-of-border plants. They a relatively easy to grow in a sunny, well-drained location and like to be fed a high potash feed during their flowering season.
Over winter, make sure they are heavily mulched with wood chippings to protect them from hard frosts.
Agapanthus mainly come in blues and lilac varieties, but you can buy them in white (‘Albus’, ‘Snowy white’, ‘Ever White’ and ‘White Heaven’).
My agapanthus did not flower in its first season last summer, so crossing my fingers for this summer.
Flowers: May – October (until the first frost)
Verbascum is going to be my next addition to my border, due to its ability to reach 2m high and long flowering season (June-October) – they are also loved by pollinators. If a plant can give me colour for 4 months and is loved by bees, it goes down on my ‘potential list’ for more research!
Verbascum like well-drained soil and full sun, but will be OK in partial shade. A lot of verbascum varieties are biannuals; they will grow foliage in the first season and flower in the second, then die off.
Like delphinium, verbascum come in a large variety of colours to suit any colour scheme in the back of a sunny border. I particularly like the award-winning ‘Verbascum Gainsborough’, a perennial plant with semi-evergreen leaves.
Flowers: June – September
Hollyhocks are usually biannuals but well worth their short-lived life span. They produce 2m high stems that are packed with large, bee-loving, flowers. They also come in a good variety of colours; currently, we have ‘black knights’ growing which contrasts wonderfully with other colours.
Hollyhocks have been grown for centuries in classic English gardens, originally for Turkey and Kurdistan. Hollyhocks are easy to grow from seed; simply soak for 12 hours in water and plant in soil.
After growing some last year, I really didn’t like the look of them after flowering. The leaves also got hollyhock rust and the whole plant looked dreadful.
Red Hot Pokers (Knipohia)
Flowers: June – October
We recently covered Knipophia in a previous post as we planted kniphofia bulbs last month and are very excited about them flowering. They look spectacular when flowering but can look ugly in autumn.
Flowers: May – July
Most of the plants we have covered peak at around 1.5-2m in height. If you are looking for something slightly smaller with lots of colours, then consider lupins; most varieties reach a maximum height of 90cms.
Most lupin varieties will flower slightly earlier than most on this list, around May time through to July – they add colour after your spring flowers before the summer bloomers take the stage.
If you are specifically looking for a tall evergreen border plant, try the Lupinus arboreus, which can also be used for privacy as it can be bushy with 2m spread.
Lupins are also very easy to grow from seed, one of the few of my seedlings that have actually survived this month.
Heliopsis (False Sunflower)
Flowers: July – September
Heliopsis is another great tall perennial to grow, which can sit in the middle or the back of a border, depending on your plant arrangement. Heliopsis is great for extending your border colour into Autumn as it tends to flower from July to September and often well into October.
Heliopsis is easy to grow in a well-drained, sunny border and prefers heavy clay soil. Heliopsis is clump-forming, so you may need to divide the plant up when it outgrows its current location.
Digitalis Purpurea (Foxgloves)
Flowers: May – July
Foxgloves are native to the UK and come in many varieties, avoid dwarf foxgloves if you are planting them at the back of a border – I made this mistake last year.
Foxgloves tend to flower in early summer, from May to July and are great for attracting bees.
Tall foxglove varieties include Digitalis ‘Polkadot polly’, Digitalis ‘Sutton’s Apricot’, Digitalis ‘Pam’s Choice’ – all of which will grow to over 1M tall in the right conditions.
Cynara cardunculus (Cardoon)
Flowers: June until first frost
Cardoons are huge perennials that can tower above most herbaceous border plants, their thistle-like head reaching for the stars. They are related to the globe artichokes and can also be eaten.
Along with the above plants, you can add a trellis to your border wall or fence and plant clematis, which can climb to over 4 metres. You can also buy an
Tallest Border Perennials FAQ
What is the tallest flower in the world?
The tallest flower in the world is the sunflower with a Guinness world record of 30 ft and 1 inch.
The flower with the ‘tallest bloom’ in the world in the world is titan arum (Amophophallus titanum), the tallest reaching 10 feet 2.25 inches. Titan arum is found in the rain forests of Indonesia.
What is the tallest flower in the UK?
According to the BBC, it’s another Titan arum grown at the Eden Project in Cornwall at 9ft 3″, but there are taller sunflowers than this for sure if you include the stem. There are also Echium Pininana documented at over 14ft tall.
What is the tallest UK native flower?
The tallest UK native flower would be the common honeysuckle (lonicera periclymenum) which can reach 7 metres high, but is a climber and requires some kind of support to reach its height potential.
What is the tallest annual plant to add to a border?
Helianthus annuus ‘Russian Giant’ can grow to 3M tall and is one of the tallest annuals. Cosmos bipinnatus ‘Versailles Dark Rose’ can also grow to 2.5 M, but the average size is 1-1.5 metres.
How do I add vertical interest to my garden?
Any of the above-mentioned plants will add spectacular vertical interest, especially if matched with well thought out companion plants. You can also buy a garden obelisk and plant climbers.
Best tall plants for the back of a shady border?
You will be mainly restricted to shrubs, but you can find many that will add colour like Hydrangea. If you are looking for perennials, consider Geranium ‘Orion’ which can reach 80cm in height. If you have dappled shade, Anemone x hybrida ‘Honorine Jobert’ can reach 1.2 metres.
What are the best tall yellow flowers for borders?
If you are specifically looking for tall yellow perennials (around 100 cm+), consider these four plants:
- Peony ‘Bartzella’ – 80cm
- Verbascum ‘Cotswold Queen’ – 1M
- Rudbeckia – 1M- 3M
- Achillea filipendula ‘Cloth of Gold’ – 1.5 M
Gareth is the owner of Plantsman Media. Gareth lives in the North East of England and is obsessed with flowers. He has just started RHS level 2 certification.