Seed heads, deadheading & post-bloom care

Val Bourne / 14 July 2015

Do you deadhead, allow to go to seed or cut down completely? Gardening expert Val Bourne recommends what you do with plants after flowering.



Tall perennial maintenance

Position tall perennial borders in good light so that the plants develop sturdy stems. This will negate the need to stake.

Leave most of the stems intact over winter to catch the frost and winter light. This will prevent your garden from having the bare-earth look in winter.

The border will sustain birds, such as finches, wrens and tits, because they will feed on the stems. It will also provide shelter for hibernating insects that might include ladybirds.

Leave the clumps of plants to mature, but be aware that some are stronger and may make wide clumps that might push others out.

If you decide to lift and divide, do so in spring just as the plants break into growth.

Most weeding will take place in early spring too, just after the border has been cut down, but before the plants are too tall.

Most seed heads can be left alone. However you may want to restrict aconitums and sanguisorbas from self-seeding, because they do so rather enthusiastically. Snip off the heads as the flowers fade.

Please be aware that aconitums are very toxic. Wear gloves and handle them carefully.

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Seed heads - a mixed blessing

Do I or don’t I?

One of the skills of gardening is knowing whether to cut off the seed heads or not.

It can depend on gardening style and position. In a large area devoid of choice plants you may be glad of lots of seedlings, however in a small garden they will soon overrun you, so those with smaller gardens often snip off their seed heads, perhaps leaving one or two at most.

Reduce over-enthusiastic plants

This is an excellent strategy with certain over-generous plants and these include aquilegias, foxgloves and Welsh poppies (Meconopsis cambric). Left to self-seed you will get far too many.

Not on the compost heap!

When you cut them off, dispose of them in the green waste bin for, if you add them to the compost heap, they will reappear as you spread the compost over, or dig it in.

Hybrids and choice plants

If a plant is a highly bred hybrid, such as a prized oriental hybrid or Helleborus x hybridus, the seedlings will often be completely different from the parent and almost certainly not as good in most cases.

Remove the seed heads of any plant that you really value - especially if it’s a hybrid with an x in the name. This will keep the vigour in your pride and joy. Producing lots of seeds is a drain on a plant - rather like a mother having lots of children.

Respecting the season

Seed heads can and do look wonderful in autumn and winter, but one of the best ways to keep a garden looking fresh in the second half of summer is to remove any touches of brown - whether it be teasel heads or some other fading plant.

This is another good reason for removing spent flowers before they fade from late summer onwards.

Deadheading

Snipping off fading flowers encourages more in many cases.

As phloxes, campanulas and other herbaceous plants fade it is worth cutting the spent flowers off. Repeat-flowering roses, all annuals and many perennial flowers, when denied the opportunity to set seed, just flower again.

Hardy annuals

Annuals can be snipped and snipped again to encourage flower, but in mid-August it’s a good idea to leave some of your plants alone so that they set seeds that you can collect later.

Collect seeds on a fine day, around midday, and then allow the seeds to dry on a tray. Clean up the seeds. Place them in an envelope with a neatly written label and put them in a biscuit tin in a dry, cool place.

Sow most of your seeds in the following spring - in early April. This applies to calendulas, nigella, African marigolds, cornflowers etc.

However some umbellifers (Orlaya grandiflora, Ammi majus and A. visnaga) are best sown in September because they develop into better plants when they have a winter outside. Ladybird poppies (Papaver commutatum) also do best autumn-sown - which is what happens to hardy annuals in the wild. Sweet pea seeds can be collected and sown in autumn too.

Perennials

Most perennials produce seeds in late-summer and most are best sown as soon as the seeds are ripe. Some may need a cold period (called vernalisation) before they germinate in the following spring - so be patient. Peony seeds, for instance, can take up to three years before they emerge from the seeds. Primrose seeds normally come up in the following spring.

Tricking Seeds

Putting the sown potfuls of seeds in the fridge for four weeks will promote precocious germination and help to shorten the process. They will usually germinate after their period of cold.

General advice about seed sowing

Use clean 9cm/3in round pots because the corners of square pots tend to hold water.

Fill the pots up with a seed sowing compost that’s low in nutrients, leaving a space at the top to allow for watering.

Before sowing, water your pots of compost using tap water that’s been allowed to stand so that any chlorine escapes.

Do not use water from a water butt. It is not suitable for seedlings because it may spread diseases.

Sow your seeds and label.

If the seed is fine lay it on the surface rather than trying to cover it.

Keep on the dry side.

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The opinions expressed are those of the author and are not held by Saga unless specifically stated.

The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.