This one seemed to be over rather quickly, with many entries going in during my first pass through the clues (there would have been more but some clues seemed to be too easy to be true so I delayed entering the solution until I had some checked letters to confirm that my original parsing had been correct).
Across
1 Trucks in film before parking in marketplace reversed (7)
PICK-UPS – PIC (film) P (parking) in SUK (marketplace) reversed
8 Give up / resistance (4)
KICK – double def.
11 Name borne by hermit once sadly missing old ornamentation (10)
ENRICHMENT – N (name) in (borne by) an anagram (sadly) of HERMIT [o]NCE
12 Loaf too much in filthy place (6)
STOTTY – OTT (too much) in STY (filthy place)
13 Desert evil, acting with independence (5)
SINAI – SIN (evil) A (acting) I (independence)
15 Place flowers and sticks (8)
PLASTERS – PL (place) ASTERS (flowers)
16 Mean, merely parting with shilling (5)
IMPLY – [s]IMPLY (merely parting with shilling)
18 Radiation detector put in school with warning light (5,7)
SPARK CHAMBER – PARK (put) in SCH (school) AMBER (warning light)
20 Weed caught smothering earth around stone (12)
HEDGE-MUSTARD – HEARD (caught) around (smothering) DUST (earth) around GEM (stone)
24 Settled hostilities only in print (5)
LITHO – LIT (settled) HO (hostilities only)
26 Cakes being stale get thrown out (8)
GALETTES – an anagram (thrown out) of STALE GET
27 Wind up in field, first to last (5)
ANGER – RANGE (field) with the first letter move to the end (first to last)
28 Knotty hoax to occupy intellect (6)
NODOUS – DO (hoax) in (to occupy) NOUS (intellect)
29 Fault in public hydrant with injurious consequence (10)
OVERTHRUST – OVERT (public) H (hydrant) RUST (injurious consequence)
30 Vacation finally in view? It can be spent in Samoa (4)
SENE – [vacation]N (vacation finally) in SEE (view)
31 Confusion in all sections revolutionary desired (7)
ASPIRED – PI (confusion) in AS (all sections) RED (revolutionary)
Down
2 Excess piece, remnant abandoned (12)
INTEMPERANCE – an anagram (abandoned) of PIECE REMNANT
3 Leap ahead during course in church (8)
CROUPADE – UP (ahead) in (during) ROAD (course) in CE (church)
4 Fibre in outfit with acceptable length (5)
KITUL – KIT (outfit) U (acceptable) L (length)
5 Philosophy leader partly provided for tribe (5)
PHYLE – hidden in (partly) ‘philosoPHY LEader’
6 Duck in silence stuffed with substance (6)
SMEATH – SH (silence) around (stuffed with) MEAT (substance)
7 Saviour having influence, releasing book after muddle (7)
MESSIAS – MESS (muddle) [b]IAS (influence, releasing book)
8 Be offensive, going over contracts (5)
KNITS – STINK (be offensive) reversed (going over)
9 School in Thrace worked on Greek character with purpose (12)
CHARTERHOUSE – an anagram (worked) of THRACE plus RHO (Greek character) USE (purpose)
10 Dimension in elevated customs after food showing emperor’s status (9)
KAISERDOM – KAI (food) D (dimension) in MORES (customs) reversed (elevated)
14 When following desire, losing weight, consumed by great madness (9)
MISHEGAAS – [w]ISH (desire, losing weight) in (consumed by) MEGA (great) AS (when)
17 Novel about Raj coming to screen (8)
ABAT-JOUR – an anagram (novel) of ABOUT RAJ
19 Bird shakes trellis to some extent (7)
KESTREL – hidden in (to some extent) ‘shaKES TRELlis’
21 God in front of Adam after pleasure with sinking heart (6)
MITHRA – MIRTH (pleasure) with the R moved to the end (with sinking heart) A[dam] (front of Adam)
22 Steward on day before festival (5)
REEVE – RE (on) EVE (day before festival)
23 Negative effects, very high without love, rising (5)
DENTS – ST[o]NED (very high without love) reversed (rising)
25 Country mostly about right for lemur (5)
INDRI – INDI[a] (country mostly) around (about) R (right)
I now remember nothing about solving this, but I see I queried 20ac, as I couldn’t parse it. Thanks for the explanation.
20a also has culinary uses, but then so do a lot of ‘weeds’.