When to plant out annual flowering plants for vibrant, colourful garden borders – and give them the best start, according to experts

Wondering when to plant out annual flowering plants for the best results? You’re not alone. These colourful, fast-growing favourites are perfect for giving your flower bed ideas an instant lift – but only if you stick to their schedules.

Yes, whether you're interested in bedding plants for shade or full sun, the good thing about these vibrant little blooms is that there is one to fit almost any garden, whatever its size or aspect.

Still, once you’ve chosen the blooms that will grace your garden borders, it’s time to get to know these Goldilocks-style plants. Plant them too early, and a cold snap could undo your hard work; too late, and you risk missing that wow-factor window. Timing really is everything – you need to get this just right…

'Bedding plants are an easy and beautiful way to brighten up a garden, patio or balcony with lots of colour and interest,' says Morris Hankinson, director of Hopes Grove Nurseries.

Morris Hankinson

Morris Hankinson is the founder and managing director of Hopes Grove Nurseries Ltd, the UK’s only specialist grower-retailer of hedging plants. He established the thriving business in 1992, shortly after graduating with a Commercial Horticulture Degree from Writtle College, Essex.

'Being annuals, they will not tolerate really cold conditions,' he continues of these cottage garden staples.

'With that in mind, it’s important to know when to plant out bedding plants by keeping an eye on frost dates for your area and cold weather spells.'

Of course, the advice will shift ever so slightly depending on which variety of annual flowering plants you've chosen, because these are so much more than just filler plants for sparse flower beds.

When to plant out annual flowering plants in summer

If you're not sure when to plant out annual flowering plants, don't be too embarrassed; it's likely because the advice is different depending on which ones you're working with.

'In the UK, the general guideline for planting out summer annual flowering plants is after the last frost, which typically means late May to early June, depending on your location,' explains landscaper and gardening expert Steven Bell.

'Plants such as petunia, calibrachoa, lobelia and surfinias will not survive frosty conditions. However, they can be planted in pots, containers and hanging baskets during late April and kept undercover until temperatures warmed up. A greenhouse, for example, is ideal,' explains Morris Hankinson of Hopes Grove Nurseries.

'Some plants need a little longer to grow, so this is an ideal way to bring trailing begonias and pretty geraniums along. Anything planted undercover first will need to be hardened off before being planted in their final growing place,' he adds.

Steven Bell

Steven Bell is an experienced landscaper, with years of experience owning paving and gardening companies. Combining hands-on expertise with a deep appreciation for sustainable landscaping practices, Steven enjoys sharing his insights with readers to inspire their own green-thumb adventures.

'Areas further south may be safe from mid-May, whereas northern or more exposed areas might be better waiting until early June,' he continues. 'The key is to ensure that the risk of frost has fully passed, as most bedding plants are tender and won’t tolerate cold temperatures.'

There are a few things you can do to help prevent transplant shock, Steven says, offering up the following top tips:

• Always check the weather forecast before planting.
• Choose a mild, overcast day for planting to reduce transplant shock.
• Prepare the soil well with compost and water in thoroughly.

When to plant out autumn and winter annual flowering plants

Knowing when to plant out annual flowering plants is every bit as important if you're working with autumn and winter varieties, such as pansies, violas, and wallflowers.

'For these, you would typically plant them out in September to October so they can establish before the coldest months set in,' advises Steven.

When to plant out annual flowering plant plugs

If you're growing your annual flowering plants from seed or plugs indoors or in a greenhouse, the advice changes ever so slightly again.

'You can start them earlier in spring and harden them off for a week or two before planting them out. This involves gradually acclimatising them to outdoor conditions –start by placing them outside during the day and bringing them in at night for about 7–10 days,' explains Steven.

It's well worth the effort, especially if you choose to work with some of the bedding plants that slugs hate most.

What temperature is too cold for annual flowering plants?

It can be too cold for annual flowering plants, particularly if you have frosts or temperatures are sitting at below or just above freezing point. Thankfully, there is hope for those who have planted theirs out too early.

'If the temptation to plant out bedding has been too hard to resist, keep a close look at the weather and either bring them undercover or cover with horticultural fleece in cold weather, especially during a frosty period,' advises Morris Hankinson of Hopes Grove Nurseries.

Shop annual flowering plants

Now that you know when to plant out annual flowering plants, it's time to figure out which ones you'll be filling your garden with.

Personally, though, we'll be racing you to the checkouts for the last few geraniums. May the speediest gardener win...