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How to build raised beds – page �
How to build raised beds
This leaflet has information to help you if you want to build a raised bed yourself or if you need information to give to a professional contractor.
This information should be read in conjunction with Thrive’s general information leaflet, Raised beds, which has information on how to decide whether a raised bed is what you need, where to put a raised bed in your garden, different ways to construct the beds and what to grow. This leaflet is available from Thrive, call us on 0118 988 5688.
What is the recommended height and width for a raised bed?
• It’simportanttothinkaboutwhat’smostcomfortableandpracticalforyouwhenyouaregardening.Also,considerwherethebedwillbepositionedandwhetheryoucanstandorsitnexttoonesideofthebed,orwhetherbothsidesareaccessible.
• Width Thewidthofaraisedbed,whichyoucanaccess
frombothsides,canbeupto1,000mmwide.Atthiswidthyoushouldbeabletoreachallareasofthebedwithease.Thelengthofthebedwillthenbedeterminedbythespaceyouhaveavailableandhowbigyouwantthebedtobe.
Ifyoucanonlyaccessthebedfromoneside,themaximumwidthisaround500mm.
• Height Theheightofaraisedbedwillbedeterminedby
what’sbestforyou.Thinkaboutwhetheryougardenstanding,sittingorkneeling,whetheryou’dliketositontheedgeofthebedandhowitwilllookinyourgarden.
Thistableisaguidetotheheightandwidthofraisedbeds,butcheckthemeasurementssuityoubeforedeciding.
Your needs: Height of bed Maximum width of bed with access one side only
Standing 900–1,000mm 500mmSitting 690–760mm 500mmWheelchair user 615mm 500mm
How to build raised beds – page �
How to build raised beds
Construction and safety
Whetheryouchoosetobuildthebedyourself,oremployaprofessionalbuilder,willdependonyourskillandbudget.Bedsusingstoneorbrickmightbebestlefttoexpertsunlessyouhavebuildingexperience.
Safetyisextremelyimportant–thebedmustbecapableofbearingtheweightofthesoil.Ifindoubt,alwaysconsultaprofessional.
What material do I choose?• Doesthematerialfitinwithyourgardenandother
landscapingmaterials?• Doesitsuityou?Forinstance,awidetoptothe
bedincreasesthedistanceyouneedtoreachacrosstogettothesoil.
• Isthematerialeasytouse,anddoesitmatchyourbudget?
What does each of the construction materials offer?
Paving slabsOneofthesimplestwaystobuildaraisedbediswitholdconcretepavingslabs(900mmx600mmx50mm).Setinthegroundonend,thesecanbeusedtomakeasimpleraisedbedtoamaximumheightof600mm.
Thepositivesofpavingslabsare:o theyarerelativelycheapandlonglastingandthe
narrowprofilemakesiteasierforyoutoreachovertheslabandintothebed
o pavingoffersachoiceofinterestingcoloursandtexturesbutconsidercarefullybeforechoosing.
Thethingstoconsiderare:o pavingslabscanlookstarkandbox-like,andyou
canonlybuildrectangularorsquaredesignsinmultiplesoftheslabsizes(unlessyoucuttheslabswithaspecialisttool)
o slabsneedtobeinstalledwithcare,ortheywillleanoutwardsandbecomeunstableandwilllookunsightly.
How to build raised beds – page �
How to build raised beds
Fig. 1Simple raised bed using 900×600×50mm flagstones Section
50mm
soil level
permeablelayer
400mmtop soil
200mmsmall-gradehardcore
300mmhardcore
subsoil
hardcore
paved surface
variable heightas needed
Diagram �: Construction using paving slabs
How do I build it using paving slabs?Tomakeastablebeditshouldbebuttedagainstpavingwithonethirdofthe900mmslablength(300mm)buriedintheground.Ifhowever,youarebuildinginsoilwithnopaving,theslabmustbeburieddeeper,around60percentbelowgroundlevel(600mm).Takecarehandlingtheslabs–theyareveryheavyandawkwardtomove.
• Digoutthegroundtoadepthof300mm(seeabove)andtothewidthandlengthofbed,leavingstraightsides.
• Breakupthetrenchsurfacewithafork,fordrainage.
• Putinyourslabs,andfixintoplacewithaloose300mmlayerofhardcore.
• Leveltheslabsverticallyandhorizontally,usingaspiritlevel.
• Sealthegapsbetweenslabswithheavy-dutyadhesivetape.
• Tampthehardcoredownverywellwithatampertool.
• Adda200mmlayerofsmall-gradehardcoreandtampdown.
• Laydownapermeablemembranetokeepthehardcoreinplace.
• Fillwithtopsoilorcompostsuitableforyourplanting.
How to build raised beds – page �
How to build raised beds
Softwood boardsForarelativelycheap,rusticlook,youcouldoptforabedusingpressure-treatedsoftwoodboardsfixedhorizontallyontostakesdrivenintotheground.
Thepositivesofsoftwoodboardsare:o softwoodischeapanddoesn’tneedagreatdealof
skillorstrengthtouseo thereisnoneedforfoundations
How do I build it using softwood boards?• Use25mmx150mmpressuretreatedsoftwood
board,whichyou’llneedtocuttothelengthsrequired.
• Place1,000mmx50mmx50mmstakesatcornersandatevery1mlength.
• Drivethestakesintotheground,toleave450mmaboveground.Insoftconditions,use550mmstakesandbury60percent(600mm)belowground.
• Checkthestakesarestraightverticallyandhorizontallywithaspiritlevelandalsochecktheyareallinthegroundtothesameheight.
o thewoodcanbepaintedorstainedtolookattractiveandfitwithyourgarden.
Thethingstoconsiderare:o thewoodhasalimitedlifespano asthewoodisnotparticularlystrong,the
maximumheightofthebedis450mm.
• Setthelowestboards50mmbelowgroundlevel. Aftercheckingthelevel,fixtheboardstothe
stakeswithgalvanisednailsorscrews.Buttthenextrowofboardsuptothefirstandfix,andsoon.
• Sealanygapswithwaterproofself-adhesivetapeontheinside.
• Toimprovedrainageinthebed,breakthesoilsurfaceuptoadepthof300mmwithagardenfork.
• Fillwithsoilorcomposttosuit.
450mmtop soil
200mmsmall-gradehardcore
Fig. 2Softwood board design Section
50mm
top soil etc(as Diagram 1)
ground level
subsoil
1000mm
450mm
150×25mm pressure-treated
softwood board fixed to 50×50×1,000mm
stakes at 1,000mm centres fixed with
60mm galvanised nails
25mmpolythenesheet
permeablelayer
Diagram �: Construction using softwood boards
How to build raised beds – page �
How to build raised beds
Timber posts or ‘palisades’Usingstronguprighttimberpostscangiveyouanattractivenaturallook,andoffersmoreflexibilityinthedesign.Thiswoodisavailablein75–200mmthicknesses,inaroundorsquaresection–andinarangeoflengths.
Thepositivesoftimberpostsare:o anatural,attractiveandsturdydesigno youcanchooseamorevariedshape,withcurves
orheightvariations
How do I build it using timber posts?• Markoutthedimensionsofyourbed.• Diga400mmwidetrenchandmakeitthesame
depthastheheightyouwantthebedtobeabovethegroundlevel.Yourbedoutlineisthecentreofthetrench.
• Putina200mmlayerofgravel.• Settheuprightpostsinplaceinthemiddleofthe
trench,buttedtogether.• Checkthattheyarelevelverticallyandthatthe
topsareflushandlevel.
o nojointsareneededo relativelystrongandlonglasting.
Thethingstoconsiderare:o foundationsareneededo handlingandcuttingthepostsneedssome
strength.
• Pourina200mmlayerofconcretetofixthepostsinplace.
• Putsoilintothetrenchtogroundlevel.• Linethesidesofthebedwithawaterproof
membrane.• Breakupthesoilsurfacewithafork.
Section
concretefoundation
gravel
400mm
Fig. 3Timber pallisades
ground level
subsoil
ground level
100mm polythenesheet
200mm200mm
200mm
variable
chamferedtop
top soil
200mmsmall-gradehardcore
permeablelayer
Diagram �: Construction using timber posts
How to build raised beds – page �
How to build raised beds
Railway sleepersAbedmadefromrailwaysleeperswillbeextremelystrongandlonglasting,withanattractivenaturallook.Sleeperscomeinastandardsizeof250mm×200mm×2,400mm.
Youcanusethemhorizontally,orcuttheminlengthandlaytheminthesamewayastimberposts.
Sleepersarewide,whichmeansyouhavetoreachfurthertogettothesoil.Tohelpminimisereachingacross,youcanlaythemontheiredge.
Thepositivesofrailwaysleepersare:o theyarefairlyeasytosource
How do I build it using railway sleepers?• Markoutyourbedarea.• Cutthesleeperstolengthandcuttheendsto
overlapatcorners(seeDiagram4).• Sinkthebottomsleepersintothegroundtohalf
theirdepth.• Drillholesinthesleepersat1mcentres,25mm
wideby75mmdeep.• Tap150mmlongdowelsintotheholes.• Fixthenextlayerofsleepersbylockingdowels
intomatchingholes.
o theyareattractiveo longlasting–somecanbeguaranteedfor15yearso youcanusetheextrawidthtogiveyouseating,or
leaningplaces.
Thethingstoconsiderare:o usedlengthways,youcanonlymakesquareor
rectangularbedso veryheavytohandleo transportcanbecostly–findalocalsourceo fixingrequiresskill,strengthandpowertoolso thepreservativecanbetoxictosomeplantsand
canstainclothesandhands.
• Drillandfixthenextlayerofsleepers.• Atcornersand1mintervalsdrive1,000mm×
75mm×75mmstakesintothegroundinsideyourbed,buryinghalftheirlength.
• Attacheachsleepertothesupportstakesusing200mmcoachbolts.
• Linethebedwallswithpolythenetostoppreservativeleachingintothesoil.
• Layhardcore,permeablemembraneandthenthesoil.
Diagram �: Construction using railway sleepers
Fig. 42400mm × 250mm × 200mm pressure treatedrailway sleepers – laid horizontally Section
sub soil
top soil
ground level
200mm polythenesheet
1,000mm
250mm 25mm coach bolts at 1,000mm centres
25mm diameter dowel peg 150mm
long. Insert at 1,000mm centres
permeablelayer
How to build raised beds – page �
How to build raised beds
BrickBrickisattractive,versatileandlonglasting.Ifyoufeelconfident,asimpleverticalwallbedbelow600mmhighcouldbebuiltasaDIYproject.Youwillneedtouseanexpertifyouareplanninganythingover600mmhighor6mlong.
Thepositivesofbrickare:o brickisthemostversatilematerial,witharangeof
coloursandtextures
How do I build it using brick?• Markoutyourbedarea.• Diga500mmwidetrench375mmdeepwiththe
bedoutlineasthetrenchcentre.• Layaconcretefoundation150mmdeepusing
1partcementto2½partssand,3½partsgravel.• Laythreecoursesofbricks,twobrickswide,in
thecentreofthetrench.Themortarmixis1partcementto3partssand.
• Youhavenowreachedgroundlevel.Laytwocoursesofengineeringorclass5bricksasadamp
o flexible–youcanvarytheheight,makeindentations,andevencurves
o durable.
Thethingstoconsiderare:o costofmaterialsandlabouro needsexperiencedlabourforanythingmorethan
asimple,straight,lowstructure.
course,usingwaterproofmortar.• Leave75mmdrainageholesevery2matthebase.• Continuewithcoursesofstandardbricks.• Topwithchamferedcopingbrick,fixedwith
waterproofmortar.• Preparethebedwithhardcore,permeable
membraneandthenthesoil.• Thegroundsurfaceshouldslopeawayfromthe
bedwallsslightlyfordrainage.
Diagram �: Construction using brickFig. 5Simple brick or block-build raised bed Section
vertical damp-proofmembrane
top soil
150mm
75mm weepholes at 2m centres
Chamfered coping
ground level
sub soil
If the wall is two-brick thickness – 215mm thick
then ties need to be provided at 450mm vertical
centres and 900mm horizontal centres.
Class 5 orengineering brick
waterproofmortar
waterproof mortar
500mm or 300mm forsingle brick thickness
bituminouspaint
215mm or102mm (single brick thickness)
foundations
200mmsmall-gradehardcore
permeablelayer
How to build raised beds – page �
How to build raised bedsFig. 6Brick or block build raised bed with toe holefor close working Section
vertical damp-proofmembrane
75mm
300mm
110mm
200mm compactedshingle fill
300mm
150mm
subsoil
compactedhardcore
ground level
engineering brick
Stainless steel tiles at 450mm vertical centres –
900mm horizontal centres
215mm
foundations
100mm
waterproofmortar
chamfer
1× 100mm drainage pipeper sq. metre
70mm40mm
300mm
Diagram �: Construction using brick with toe hole for close working
Diagram6showsamoresophisticatedrecesseddesignwithafulllengthtoeholeformorecomfortableworkingifyouwanttogardenfacingforwards.
ThriveisregisteredintheUKastheSocietyforHorticulturalTherapy.Thriveisaregisteredcharity(number277570)andasalimitedcompany(number1415700).
ThisleafletcopyrightThrive2008.PhotographscopyrightCarolineNieuwnehuysandThrive2008.
Thrive,TheGeoffreyUdallCentre,BeechHill,Reading,Berkshire,RG72ATT:01189885688E:info@thrive.org.ukW:www.thrive.org.uk
We hope this information has been of help.
Likebrick,reconstitutedstonehassimilarversatilequalities,andcomesinstandardsizesforeaseofuse.Takeadvicefromyoursupplieraboutthebestwaytolayit.
Soil
Thebonusofusingraisedbedsisthatyoucanchoosethesoilthatwillbestsuityourplanting.Ifyouplananalpinebed,orabedforplantsthatlikelimeysoil,preparethebedaccordingly.
Asageneralrule,smallerraisedbedsarelikelytolosesoilnutrientssooner.Ideally,amixof50percentsterilisedgardensoilorloam,50percentpeatbasedorpeatsubstitutecompost,andslowreleasefertilizershouldgiveyougoodresultsinthefirstyear.
Thebedmayneedtoppingupwithsoil/compostagainin12months.Afterayear,topdressingsofliquid
feedsorfertilizershouldkeepnutrientstoagoodlevel.
Toimprovemoistureholdinginthebed,applyamulchofyourchoicesuchasfinebarkchippingsorgravel.
Thesoilinthebedwilltaketimetosettleandwillneedtoppingup–thissettlementcouldtakeafewyearsinhighraisedbedssojustplantannualsorvegetablestostartwithandleavepermanentplantingforlater.
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