By Ruth Hayes
Trying to decide what to plant in September to ensure there's still plenty to enjoy in your plot over the coming months? We're here to help with our easy guide on what to plant over the coming weeks.
September can be a wistful time as we move from the heat and colors of summer to the cooler temperatures and russet hues of the fall. But this isn’t a time to give up on the garden, far from it. As summer annuals fade and are removed and we cut back perennials as they reach the end of their yearly display, we are left with gaps to fill.
So if your flowerbed ideas and borders are starting to look a little threadbare, now is the perfect time to get planting to rejuvenate them for the coming months.
What to plant in September: 10 picks to fill your garden with now
Whether you want some instant color with pretty bedding plants or want to sow seeds or plant bulbs ready for early spring displays, our suggestions for what to plant in September will ensure there is plenty to admire in your plot during the cooler weather ahead.
Whatever flowers you plant this month, don’t forget to keep them well watered while they get established, especially as September can often give us a warm, dry Indian summer.
Soil may also need enriching after a summer of growing, so dig in lots of well-rotted compost or manure, which will feed your new plants and also help the ground hold onto moisture.
Chrysanthemums, also known as ‘chrysanths’ and ‘mums’ were all the rage for a while, then fell out of favor and gained a reputation for being a bit boring and fuddy-duddy.
Now they are back in vogue and a top garden trend, so more people are enjoying the benefits of learning how to grow chrysanthemums. It's easy to see why too. Easy-going and with a wide range of colors, flower sizes and heights, they are the slightly less flashy cousin of the dahlia and just as beautiful.
Although most chrysanthemums are bought as rooted cuttings and small plants in spring, garden centers and online suppliers will have lots of fantastic, bright bedding varieties in stock now, making them an easy addition to your list of what to plant in September.
These are usually dwarf plants that form clumps of gem-shade flowers in pinks, reds, russets and oranges. They will flower long into the winter and again next spring.
Top tip: Deadheading flowers regularly will keep the blooms coming and the plants in a neat shape.
2. Biennial seedlings
If you sowed a selection of biennials in spring and summer, the seedlings should be ready to move to their final growing place.
Biennials are plants that are sowed year and flower the next, and they include foxgloves, sweet rocket, wallflowers and honesty.
Many of these plants will happily self-seed around the parent plant so if you are already growing them you may find seedlings springing up in unexpected (and unwanted) spots in your garden.
Carefully dig them up, keeping soil around the roots, and plant them where you wish, at the same depth as they were growing before. Keep them well watered.
Alternatively, pot them up in peat-free compost and overwinter them in a cold frame or unheated greenhouse. Next spring, when the soil warms up, you can plant them out where you want.
Top tip: If pink and white honesty has self-seeded, either leave it where it is or add it to the compost heap if you don't want it. These plants have long, thick tap roots and don’t transplant well.
3. Spring bulbs
It is the season of planting bulbs ready for next spring's displays, which is a delight because they are so easy to add to the garden and they are the promise of colorful times ahead, just on the other side of winter.
The range of bulbs available is mind-boggling, but for an interesting, colorful mix of plants that starts in early spring and lasts right through to summer, you could plant a mix of crocuses, muscari (grape hyacinths) and Iris reticulata, as well as daffodils and narcissus, tulips, ranunculus, anemones and alliums.
Want to get the best from your daffodil displays? Our guide on how to plant daffodil bulbs has lots of expert tips.
As well as being easy to plant, spring-flowering bulbs are versatile, happy in garden borders and pots, while dwarf varieties work well in baskets, rockeries and the lawn.
Plant them pointed end up at three times their own depth, roughly one bulb’s width apart in soil that is free-draining and has been enriched with well rotted compost or manure.
Anemone bulbs look like shrivelled raisins, making it hard to know which is 'the right way up' to plant them.
Simply put them in the soil at the depth suggested on the packet and they will do the rest and grow well. These bulbs, along with and ranunculus ‘claws’, need soaking in water before planting to get the best results.
Top tip: Heavy clay soil is prone to waterlogging which will cause bulbs to rot, so if this is your soil, you may prefer to grow them in pots as part of your container gardening ideas. Plant them in containers of peat-free compost with added granular fertilizer.
With their jewel-colored flowers and interestingly patterned leaves, jaunty little cyclamen are an excellent choice for what to plant in September. They are the saviors of shady border areas and add color to even the drabbest autumn day.
Happy in shade, where they seem to glow out of the gloom, their corms will multiply over the years. They also boost their numbers by self-seeding.
The best outdoor varieties are Cyclamen coum, which have green leaves with white streaks and pretty little flowers in shades of pink, red and white, and Cyclamen hederifolium, with their pink and white flowers and leaves patterned like ivy.
Both varieties thrive in humus-rich soil and are lovely under trees and shrubs. You'll find more of the best shade-loving plants in our guide.
Tip tip: After flowering, cyclamen seedpods are held on curled stems that slowly unwind as they ripen, lowering the precious seeds down to the soil.
5. Ornamental brassicas
There's no need to laugh at this suggestion for what to plant in September! Ornamental brassicas are a far cry from soggy over-boiled cabbage and the smell of old washing.
Many of them produce brightly colored leaves in varying shades of greens with mauve, purple and steely tints to provide a cool foil to the burnished and bright colors of spring and autumn bedding, their color often deepening as the temperature falls.
Best of all, you plant them at a time when cabbage white butterflies are no longer on the wing, so there's no need to be on caterpillar watch for weeks on end!
Ornamental cabbages do well in borders and also look eye-catching in smaller planting schemes contained in pots, baskets and rockeries.
Top tip: These pretty plants are edible when they are young, though their taste is stronger than the brassicas we grow for cooking, and not as palatable.
If you'd prefer to learn how to grow winter brassicas to eat rather than purely for ornamental purposes, our guide has tips on growing everything from cabbage and cauliflower to kale, sprouts and sprouting.
If you're also considering what to sow in September and you have patience, this month is a good time to sow the seeds of Dierama pulcherrimum, or angel's fishing rods.
You need to be patient because the plants can take up to five years to reach flowering maturity, but the end result is delicate and beautiful plants with thin, straplike leaves and gracefully drooping skeins of bells – hence their name – in shades of deep pinks and mauves.
If you are already growing the plant, collect the seeds as soon as they are ripe (our guide on collecting seeds from flowers explains how to do this). When you sow, scatter seeds thinly on the surface of a tray of seed compost and don't cover with more compost or vermiculite as light is needed for germination.
Prick out the seedlings when large enough and grow on until they are reach a size that will cope with being planted out somewhere sunny with free-draining soil.
Although dierama look wonderful growing among ornamental grasses close to water, the corms that develop from their seeds as they mature are prone to rotting and need a dry site.
Top tip: Dierama will grow in containers, but are much happier in the soil. In winter, mulch corms with well-rotted compost or manure if very cold weather is forecast.
Violas are a spring bedding stalwart. Smaller and less blowsy than pansies, they are less likely to have their petals damaged by winter weather and will happily hunker down and sit out the worst of the weather before springing back to life when conditions improve.
There are many varieties to choose if you're thinking about what to sow in September, from the purple and yellow old-fashioned favorite ‘Johnny Jump Up’ to the multi-colored ‘Chicky Chicks’ and ‘Pink Halo', which have pink-mauve petals which darker inky rings and yellow centers that look like slightly squashed-up faces.
Sow the seeds in a tray of dampened seed compost, cover with a little more compost and germinate on a warm, light windowsill. Prick out seedlings when they are large enough to handle and pot them on in peat-free compost. There's tips on how to transplant seedlings in our guide.
Harden off plants in spring and plant them out when the weather warms.
Top tip: Violas and pansies are prone to a fungal disease called leaf spot, which causes oily dark patches to appear on the leaves, and weakens the plants. Avoid it by planting homegrown plants in areas of the garden where violas and pansies have not grown before.
8. Poached egg plants
Easy to grow and with sunny faces, poached egg plants (Limnanthes douglasii) are the cheeky, cheerful chappies of the spring and summer garden.
Low-growing, with vibrant green leaves and white flowers with yellow centers, they self-seed with ease and are ideal for the front of borders, as ground cover and as path edging plants.
They like full sun and are hardy, so sow them now in soil that has been cleared of weeds and stones, raked until it is fine and crumbly and watered.
Scatter the seeds thinly, cover with a little more soil and label the site so you don’t accidentally disturb them. It’s also worth sprinkling some pepper dust over the top to keep off cats and pests.
The seeds will spend winter in the soil and start to germinate when the weather warms up next spring, and will flower all summer and into the fall.
Top tips: Poached egg plants are popular with pollinators as well as insects that prey on garden pests such as aphids, so use them as a companion planting aid and sow a few seeds around your fruit and veg patch.
9. California poppies
California poppies, also known as Eschscholzia californica, are cheery annuals that spread pops of color wherever they are sown.
Hailing from – you guessed it – California, where they are the State Flower, their orange variant is the most commonly seen, though they also come in shades of brilliant red, yellow and cool cream.
Glossy flowers ride high above soft ferny leaves, and their furled petals open as the sun passes over, following it on its daily course.
Sow now in well-prepared soil and look forward to long-lasting colour well into the fall. The great thing about these flowers is they don’t mind poor soil, as long as they get lots of sun, so they are perfect for dry areas of the garden.
Top tip: Orange is the dominant color form and self-seeded offspring of differently colored California poppies will probably come up orange the following year.
10. Malope Trifida 'Vulcan'
If you are looking for a floral show-stopper that is one of the best low-maintenance plants, you won't go far wrong with Malope trifida ‘Vulcan’.
A hardy annual despite its exotic appearance, this variety of stately mallow produces a profusion of glossy pink-purple flowers with lime-green centers, making it an interesting one to add to your list of what to plant in September.
Growing to 3ft (1m), it likes a sunny, well-drained spot and although it can also be sown in spring, seeds started now will have a head start on later sowings and will flower sooner.
As an added bonus, if you sow two or three batches over six weeks, you will get a prolonged flowering season.
Alternatively, sow them undercover in trays of sieved and dampened seed compost.
Tamp the compost flat so it provides a secure surface for germination and add a lid to the seed tray. Set it somewhere light, such as a greenhouse or cold frame, and the hardy annual seeds will germinate in a few weeks.
They can be pricked out and potted on into peat-free compost and overwintered in the greenhouse.
Top tip: ‘Vulcan’ flowers are lovely for indoor arrangements but don't start cutting them as soon as they start to appear on the plant as you’ll remove lots of buds as well. Wait a couple of weeks until the plant has really got established and is throwing out lots of blooms, and then start harvesting. There's lots more suggestions for the best cutting garden flowers in our dedicated guide.
Ruth is the gardening editor of Amateur Gardening magazine and spends her working days carrying out, writing about and photographing the tasks the readers should be carrying out each week, as well as testing many of the new products that arrive on the gardening market.
She is horticulturally trained, with a qualification from the Royal Horticultural Society, and her work varies with the seasons and includes everything from sowing and planting, to pruning, taking cuttings, dealing with pests and diseases and keeping houseplants healthy. She covers ornamental plants and edible crops and everything she writes about and photographs is in her own garden, a mature plot that has been a work in progress since her family moved to their current house in 2012.
Her main interests are gardening for wildlife and organic gardening, as she firmly believes you don’t need to ‘nuke’ pests and problems with toxic chemicals, nor use peat composts to produce the garden of your dreams.
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