how to build raised beds - thrive.org.uk€¦ · raised beds railway sleepers a bed made from...
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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 as a download from Thrive’s website, www.carryongardening.org.uk, or you can 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
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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.
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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.
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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,toleave450mm aboveground.Insoftconditions,usea longer stakeif necessary.Checkthestakesarestraightverticallyand horizontallywithaspiritlevelandalsocheckthey areallinthegroundtothesameheight.
o thewoodcanbepaintedorstainedtolookattractiveandfitwithyourgarden.
Thethingstoconsiderare:o thewoodhasalimitedlifespano asthewoodisnotparticularlystrong,the
maximumheightofthebedis450mm.
• Setthelowestboards50mmbelowgroundlevel.Aftercheckingthelevel,fixtheboardstothestakeswithgalvanisednailsorscrews.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
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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
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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
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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
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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:[email protected]: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.