Deadheading is the term used for the removal of flowers from plants when they are fading or dead. Blooming perennials add beauty to any landscape beds, borders, and containers, but once the blooms start to fade they lose their attractiveness spoiling the overall appearance of the plant. Because of this these fading flowers are best removed except in some cases where seed pods may be visually attractive or needed for reproduction. Along with removing the shabby appearance of fading blooms it is beneficial to many plants helping them direct energy into stronger growth and blooming instead of seed development. Removing faded blooms, especially those that are large containing many petals such as peonies, camellias and roses, will also help to keep gardens clean from scattered flower debri.
If you are unsure as to what plants will benefit from deadheading the list below hopefully will help. The plants are listed alphabetically by their Latin name. If you aren't sure of a plants Latin name, but know its common name, you can use the list of common names at the end of this article for cross referencing.

Flowering Perennials

ACHILLEA (Yarrow) - Rebloom? Yes
Cut back stems after flowering to encourage a late season bloom. Letting seed heads remain will encourage spreading. May be invasive!

ACONITUM (Monkshood) - Rebloom? Yes
Spent flowers may be deadheaded to encourage reblooming. All parts of the plant are poisonous. Wear gloves when handling.

ACTAEA (Bugbane) - Rebloom? No
After flowers fade, leave the seed pods for winter interest if you like the look, otherwise cut back stems to the foliage. This plant is slow to establish.

AEGOPODIUM (Snow on the Mountain) - Rebloom? No
Flowers are small and insignificant and not particularly attractive. They may be sheared off at any time. Spreads by rhizomes. Invasive.

AGASTACHE (Anise Hyssop) - Rebloom? Yes
Agastache will bloom from mid-summer to fall. Deadhead to keep the plant looking neat and blooming fully. Attracts hummingbirds and butterflies!

AJUGA (Bugleweed) - Rebloom? No
Ajuga flowers mid to late spring. After flowering, the plants may be deadheaded to improve appearance. Large areas may be mowed at high setting.

ALCEA (Hollyhocks) - Rebloom? Yes
Spent flowers should be pinched off stems. Leave a few spent flowers for reseeding these biennials. When flowers are gone cut stem to basal foliage.

ALCHEMILLA (Lady's Mantle) - Rebloom? Yes?
Remove stems of spent flowers to prevent self-seeding of this plant as it tends to be invasive. This may encourage a late season, sparse rebloom.

ALLIUM (Ornamental Onion) - Rebloom? No
Allium flowers from bulbs on tall, strong stems. When it begins flowering the foliage starts to die back. Remove stems of spent flowers.

AMSONIA (Blue Star) - Rebloom? No
Native wildflower flowers. Grown in full sun will remain upright & won’t require much cleaning. In shade you may want to cut stems back by 1/3.

ANEMONE (Windflower) - Rebloom? Yes
Spreads slowly by creeping rhizomes. Blooms are long lasting and may be cut back when flower is spent to maintain a neat appearance.

ANGELICA (Archangel) - Rebloom? No
A short-lived perennial. Allowing some seed heads to remain will encourage self-seeding. Cut off spent flowers & stems as desired.

AQUILEGIA (Columbine) - Rebloom? No
Deadheading will prolong the bloom time. May self-seed if allowed to go to seed, although varieties may cross-pollinate. When the foliage fails, cut back to the ground.

ARABIS (Rockcress) - Rebloom? No
Cutting back the flowers after flowering will encourage denser, neater foliage. Foliage may decline in the hottest part of summer.

ARMERIA (Sea Pink, Common Thrift) - Rebloom? Yes
Armeria will bloom in mid-spring. Cut back the stems of spent flowers to encourage reblooming, although it will no doubt be sporadic.

ARTEMISIA (Wormwood, Sagebrush) - Rebloom? No
Grown primarily for its foliage. If foliage starts looking shabby or leggy, feel free to shear the plant back to make it neater.

ARUNCUS (Goatsbeard) - Rebloom? No
Won’t spread by self-seeding, so leave the seed heads if you like the look they provide, or cut back the stems to the foliage.

ASARUM (Wild Ginger) - Rebloom? No
Purple-brown flowers are quite small but very interesting and usually hidden by the foliage. No deadheading needed. Spreads by rhizomes.

ASCLEPIAS (Butterfly Weed, Swamp Milkweed) - Rebloom? No
Flowers and foliage attractive to butterflies. Once flowers are spent, milkweed pods (up to 4” long) form. Harvest these to prevent reseeding. The seed pods also look great in spruce tip planters.

ASTER (Aster) - Rebloom? Yes
Pinching plants back in early summer keeps habit more compact & delays blooming. Deadhead to encourage consistent blooming.

ASTILBE (False Goatsbeard, False Spirea) - Rebloom? No
Astilbe will not rebloom, so you may leave the seed heads if you like the look, or cut back spent flower stems to foliage if you prefer.

ASTRANTIA (Masterwort) - Rebloom? No
Astrantia has a long bloom period that is helped by deadheading. Spreads by stolons and reseeding, but flowers may not be true if left to reseed.

AUBRIETA (False Rockcress) - Rebloom? Yes
If you shear back the plant after flowering, you may get a second, somewhat more sporadic bloom, and the plant looks much neater.

BAPTISIA (False Indigo) - Rebloom? Yes
After flowering, the plant becomes more open & cutting back will keep the plant neat, but you’ll lose the attractive seed pods. Deadheading is not needed if you like the pods.

BERGENIA (Pig Squeak) - Rebloom? No
After Bergenia’s flowers fade, cut the stems off down to the ground. These plants will only rarely reseed themselves. Evergreen foliage.

BRUNNERA (Bugloss, Perennial Forget-Me-Not) - Rebloom? No
After flowering, reseeding may be prevented by cutting stems down to 2-3”. This plant is not invasive and will not rebloom.

CALLIRHOE (Poppy Mallow, Wine Cups) - Rebloom? Yes
Callirhoe has an extended bloom period and benefits from deadheading spent flowers and their stems. Will self-seed if allowed. Not invasive.

CAMPANULA (Bellflower) - Rebloom? Yes
Depending on variety & flower size, deadheading may be tedious, but will encourage rebloom. May spread by allowing some seed to drop. Pinch off individual flowers when they fade. When stalks are done producing, cut them back to 6” from the ground.

CENTAUREA (Mountain Bluet, Bachelor's Button) - Rebloom? Yes
Cut the spent flowers down to a side shoot. After all flowers on stems are faded, cut stem back to 2-3”. Will self-seed prolifically if allowed.

CENTRANTHUS (Jupiter's Beard) - Rebloom? Yes
Cut back faded flowers to side shoots. Often reblooms if spent stems are cut back to 3”. These plants reseed quite prolifically if allowed to set seed.

CERASTIUM (Snow-in-Summer) - Rebloom? No
Foliage forms a low-growing mound. Flowers on slender stems above the foliage. Shear after flowering or mow on high setting. Spreads by runners.

CHELONE (Turtlehead) - Rebloom? No
Allow seed pods to remain. If you like the look, they’ll add winter interest. If you find them objectionable, cut back to the foliage.

CHRYSANTHEMUM (Mum) - Rebloom? Yes
Pinching plants back until July 4th keeps habit more compact & delays blooming. Deadhead to encourage consistent rebloom.

CIMICIFUGA (SEE ACTAEA)

CLEMATIS heracleifolia (Bush Clematis) - Rebloom? Yes
Bush Clematis blooms over an extended period. Deadheading will encourage good rebloom, but the fluffy seed heads are attractive, too.