3 letters:
ede

4 letters:
bead, bede, cede, dede, deed, eade, fede, feed, he'd, heed, lead, leed, mead, nead, need, nied, peed, read, reed, reid, ried, seed, teed, we'd, weed, wied

5 letters:
-pede, abcde, abeed, aidid, alkyd, amiid, areed, baiid, beede, bleed, brede, breed, caede, canid, cpuid, cread, crede, creed, deede, dev.d, diede, dovid, dreed, erede, fleed, frede, freed, freid, fried, gaede, glead, glede, gleed, grede, greed, hadid, hafid, hamid, i.e.d, keyed, knead, kneed, leede, libid, m.b.d, madid, meade, o.e.d, omead, piede, plead, prede, preed, q.e.d, reede, rheed, riede, saeed, seeed, she'd, sheed, skeed, skied, smead, smeed, snead, sneed, spaed, spead, spede, speed, steed, swede, teiid, thede, theed, tiede, treed, tweed, vahid, veede, vrede, vreid, wahid, walid, weede, wrede

6 letters:
accede, adrede, agreed, amriid, anteed, asread, atrede, axseed, breede, decede, delead, deseed, emceed, exceed, expede, expeed, fareed, fleadh, friede, gilead, hameed, impede, incede, indeed, infeed, jameed, jereed, lipide, naveed, pitied, rashid, recede, remede, reread, reseed, sayiid, schede, screed, secede, shahid, sinead, spreed, streed, tawhid, thiede, unfeed, uplead, waheed, waleed

7 letters:
agamede, al-adid, allseed, aniseed, anobiid, arctiid, ashmead, ashweed, ausrede, bebleed, benweed, brighid, burweed, compeed, concede, cowweed, cudweed, decreed, degreed, despeed, diomede, discede, dispeed, dyeweed, emplead, epicede, fanweed, fitweed, ganymed, glochid, goateed, gumweed, hagseed, hayseed, hogweed, imbreed, implead, inbreed, inkneed, jamshid, jerreed, jetbead, kinrede, kynrede, laclede, letheed, limeade, linseed, lygaeid, matweed, mayweed, misdeed, misfeed, mislead, misread, mistide, monacid, mugweed, nasheed, neuwied, nitweed, oarweed, oilseed, oreweed, outrede, outweed, pigweed, pinweed, precede, preceed, procede, proceed, ragweed, rasheed, redweed, regrede, ruaridh, rurikid, schmead, schwede, seaweed, shaheed, succeed, sybreed, taeniid, tarweed, tupaiid, untread, upbreed

8 letters:
agueweed, airspeed, almsdeed, alwaleed, anisakid, antecede, aristede, aristide, birdfeed, blueweed, bullweed, bur-reed, bur reed, buzzfeed, capeweed, centiped, clotweed, cockweed, coleseed, copyread, daneweed, dasyatid, dilaudid, dillweed, downweed, duckweed, elfriede, enschede, filariid, fireweed, flambeed, flaxseed, flaxweed, flixweed, ganymede, gapeseed, goatweed, goutweed, gulfweed, hag-seed, handfeed, hawkweed, hurdleed, illbleed, imbureed, ironweed, itchweed, knapweed, knopweed, knotweed, lakeweed, lockheed, locoweed, markweed, mesaieed, milkweed, misplead, moonseed, mujtahid, neckweed, netspeed, newsfeed, nobody'd, oarsweed, octopede, one-seed, ophidiid, oribatid, outbreed, outspeed, overfeed, overlead, overread, pay heed, pineweed, pokeweed, pondweed, rapeseed, reduviid, refereed, richweed, rockweed, rosemead, s-cry-ed, silkweed, silpheed, snapweed, soapweed, stampede, strokeed, subbreed, suisuide, sylpheed, tatusiid, tee-heed, teelseed, tickseed, tickweed, tileseed, trusteed, unpitied, usamriid, vandread, wartweed, wee-weed, yaw-weed, zakspeed

9 letters:
al-tawhid, appleseed, benniseed, bergfried, blackseed, bloodweed, brookweed, broomweed, bugleweed, candyweed, cane reed, capripede, catchweed, centipede, cerripede, chafeweed, chaffweed, cheerlead, chia seed, chickweed, cirrepede, cirripede, clearweed, colicweed, crazyweed, dill seed, dill weed, disagreed, ditchweed, dodecafid, driftweed, drip-feed, drop-seed, estrildid, fern seed, feverweed, filagreed, filigreed, flamsteed, footspeed, free-reed, frostweed, gelechiid, goodspeed, grapeseed, greenweed, growthead, gypsyweed, halfbreed, hand-feed, hatebreed, highspeed, horseweed, hydroseed, intercede, intermede, janjaweed, jewelweed, jointweed, krumwiede, line feed, matchweed, microbead, millepede, millipede, mini-feed, nosebleed, notchweed, off-speed, orangeade, overbreed, overspeed, pearlweed, pedigreed, pine-weed, poeciliid, poppyseed, proofread, purebreed, reparteed, retrocede, riverweed, rosinweed, runnemede, runnymede, sand reed, saturniid, selespeed, self-seed, siegfried, sightread, skunkweed, smartweed, snakeweed, soap-weed, spoonfeed, squawweed, stellerid, stickseed, stickweed, stinkweed, stoneweed, supercede, supersede, superweed, sweetweed, symphilid, take heed, ten-speed, tick-weed, two-speed, undecreed, underfeed, waterweed, whiteweed, windspeed, witchweed, wolfspeed, womanhede

10 letters:
abdelhamid, beetleweed, beggarweed, bitterweed, black bead, bottlefeed, broom-weed, butterweed, buttonweed, cancerweed, cankerweed, carpetweed, clammyweed, colorbreed, cottonseed, cottonweed, crazy weed, creep feed, crossbreed, diphenamid, ditch reed, enterplead, euphausiid, float-feed, force-feed, force feed, friendfeed, frost-weed, garnisheed, ghost weed, giant reed, gigi hadid, gossiprede, gravelweed, guaranteed, guarantied, half-breed, heartbleed, hemerobiid, high-speed, hoverspeed, hyperspeed, interbreed, interplead, jimsonweed, libellulid, lightspeed, lymantriid, mazdaspeed, nightbreed, pearl-weed, poppy seed, prophesied, quirk bead, rabbitweed, rattleweed, rebamipide, scarabaeid, silverweed, skunk-weed, sneezeweed, spoon-feed, stall-feed, stick-seed, superspeed, thamesmead, title deed, trust deed, tumbleweed, velocipede, velvetweed, wattleseed, weak-kneed, white bead, will smeed, winterfeed, winterweed, yellowweed, zaha hadid

11 letters:
al-mu'tadid, anomalipede, bella hadid, bottle-feed, breast-feed, camphorweed, canary seed, cancer weed, celery seed, certainteed, chickenfeed, common reed, cross-breed, double-reed, double reed, dragonspeed, edible seed, fennel seed, french weed, gracilariid, groundspeed, joel embiid, knack-kneed, knock-kneed, light speed, megatheriid, oliver reed, peyton reed, pumpkinseed, rabbit-weed, rattle weed, scratchweed, sesame seed, singlespeed, tettigoniid, thimbleweed, trumpetweed, tumble-weed, unpedigreed, vinegarweed, walter reed, willow-weed, winter-feed

12 letters:
call-by-need, caraway seed, chicken feed, counterplead, crystal reed, devil's weed, english-weed, getyourguide, harris tweed, jumping seed, let it bleed, mustard seed, pickerelweed, polecat weed, prickle-weed, pumpkin seed, scorpionweed, star aniseed, trombiculiid, trumpet weed, unguaranteed

13 letters:
at full speed, best-of-breed, false ragweed, great ragweed, jabesh-gilead, mohamed hadid, mortgage deed, pickerel weed, poke milkweed, pressure feed, ramoth-gilead, scorpion weed, silkworm seed, star-duckweed, stinking weed, yolanda hadid

14 letters:
alligator weed, balm of gilead, butterfly weed, common ragweed, coriander seed, fenugreek seed, great duckweed, jamestown weed, marsh milkweed, pineapple weed, safflower seed, showy milkweed, sunflower seed, swamp milkweed, taj-ul-masajid, water flaxseed, white milkweed

15 letters:
apostles' creed, common duckweed, execution speed, house centipede, lesser duckweed, mead's milkweed, orange milkweed, poison milkweed, rheumatism weed, turpentine weed, western ragweed

16 letters:
assassin's creed, consumption weed, corn gluten feed, garden centipede, gulshan-e-hadeed, rattlesnake-weed, rattlesnake weed

17 letters:
perennial ragweed

18 letters:
berwick-upon-tweed, frances shand kydd, horsetail milkweed

19 letters:
egyptian paper reed, khalid ibn al-walid

20 letters:
operation warp speed