ACROSS
 1. _T_ _OUJOU_ R SP + DRIER* X = TOUJOURS PERDRIX <too much of a good thing>
 9. ED inside BAD = BEDAD <minced oath>
10. ←A BARB← N C_ ON = BRABANÇON <Belgian horse>
11. ←(.r)MIT AI RES(e.)← = SERIATIM <bit by bit>
12. REDDISH - R = EDDISH <stubble>
14. <driver> JEHU = J_E _H_ _U_
15. ME DIMS outside U + HIP = MEDIUMSHIP <spiritual practice>
18. (PEN + N_) inside CATCHY = CATCHPENNY <sensationalist>
19. ←EVEN← = NÉVÉ <snow which covers glacier>
21. <sucker> REMORA = (.e)RE MORA(l.)
23. CHAR LOCK = CHARLOCK <wild mustard>
26. <characteristic> LINEAMENT = LAMENT outside IN _E_
27. ←PUTS← _A = STUPA <Buddhist dome>
28. ←BART inside ILIA_← PIOUSNESS - PI = ATRABILIOUSNESS <bad temper>

DOWN
 1. <wasting> TABES = L off TABLES
 2. (THES_ ROUND)* = UNDERSHOT <driven by particular water flow>
 3. <group of eight> OGDOAD = _O_G_D _O_A_D_
 4. ←BAR← BITE YES = RABBIT-EYES <blueberries>
 5. PIANO - O = PIAN <contagious disease>
 6. _R _H _A _B _D _O _M _S = RHABDOMS <seers>
 7. R [-h]ECTI[-c] = RECTI <muscles>
 8. <shrew> XANTHIPPE = X ANT HIP + PE_
13. FIANC[-é] HET + TO = FIANCHETTO <get side piece on board?>
14. J (V off VICAR) ILL + A = JICARILLA <New Mexican>
16. (HERO outside I) (L inside DUE) = HIERODULE <temple slave>
17. <foot> CHORIAMB = (I AM) B_ after CHOR[-e]
20. CR (AS IS) = CRASIS <contraction of vowel sequences>
22. ←RANI M← = MINAR <Indian tower>
24. K_V ASS = KVASS <beer from Eastern Europe>
25. <perhaps make plastered> CEIL = C ←LIE←