Long Garden Flower Box

Dimensions

Cut list

Tools you'll need

• ✓

  Measuring tape (5m or longer)

  Used for measuring each lumber piece.

• ✓

  Pencil and carpenter's square

  Used for marking lines and checking right angles.

• ✓

  Saw

  Home center cutting service is recommended.

• ✓

  Electric screwdriver

  Using an impact driver improves work efficiency.

• ✓

  Sandpaper

  Prepare two types: #120 and #240 grit.

• ✓

  Level

  Essential for checking horizontality during assembly.

• ✓

  Clamp (2 or more)

  Used for temporary fixing when joining parts.

• ✓

  Brush and paint tray

  Used for applying wood preservative.

Materials

Build steps

1. 1

   Measurement and confirmation of installation location

   ≈ 15 min

   Measure the installation location for the Garden Flower Box (Long Size) (1200×250×250mm). Check the window frame size, water splash path during watering, and sun exposure (southeast-facing is ideal).

   Measure

   W 1200 mm

   MeasureSTEP 1 / 10

   Tip

   • Make the box width 50mm smaller than the window frame to ease installation.
   • Design so that the box is 20-30mm away from the wall to avoid wall and window stains from drainage after watering.
   • If attaching to balcony railing, measure the railing width first.

   Watch out

   • Measure the inside dimension of the window frame, not the outside; overlooking the frame thickness causes fitting issues.
   • Plants won't grow well if placed in a north-facing location with poor sunlight. Confirm sunlight duration at installation site.
2. 2

   Cutting and preparation of parts

   ≈ 20 min

   Cut SPF 1x6 lumber (12×140mm) into two front/back boards (12×140×1250mm), two side boards (12×140×250mm), and two bottom boards (12×140×1176mm). Prepare 30 coarse-thread screws 38mm. Also prepare one can of outdoor water-based wood preservative.

   Cut

   Use the in-store cut service

   CutSTEP 2 / 10

   Tip

   • Since 1x6 lumber is thin, some boards may be warped. Check straightness by looking from the end at purchase.
   • The bottom boards are two pieces each 776mm long, matched to the inside width 776mm of the front/back boards.
   • Cutting at home centers is accurate; each cut costs about 30-50 yen.

   Watch out

   • Driving screws without pilot holes easily splits the thin boards.
   • If not using stainless screws, iron screws will rust within a year outdoors.
3. 3

   Sanding

   ≈ 25 min

   Sand all parts sequentially with #120 then #240 grit sandpaper. Carefully bevel inner corners to avoid damaging plant roots. Concentrate sanding on board ends as they absorb water easily.

   Sand

   #120

   SandSTEP 3 / 10

   Tip

   • Board ends expose fibers that allow water ingress. Sealing these well with paint is key to longevity.
   • Sand both outside and inside thoroughly so plant roots do not catch on rough spots.
   • Beveling corners protects plants from injury.

   Watch out

   • Do sanding outside to avoid dust indoors since this is an outdoor project.
   • Leaving sanding dust on surfaces before painting causes rough finishes.
4. 4

   Assembly of front/back and side boards

   ≈ 30 min

   Attach side boards inside both ends of front/back boards. Apply a thin layer of wood glue on the end grain. Drill φ3mm pilot holes from the front/back boards, then drive two 38mm coarse-thread screws at each joint (4 joints × 2 screws = 8 screws). Check right angles at all corners using a carpenter's square during assembly.

   Build the frame

   Tighten joints firmly

   AssembleSTEP 4 / 10

   Tip

   • Since 1x6 lumber is 12mm thick, 38mm screws appropriate for bonding the two bottom boards plus glue thickness.
   • Always drill pilot holes first as 12mm boards easily split.
   • Immediately wipe off excess glue with a wet cloth.

   Watch out

   • Driving 38mm screws without pilot holes splits the 12mm-thick boards.
   • Too much glue squeezing inside may prevent paint adhesion.
5. 5

   Bottom board attachment and drainage hole processing

   ≈ 25 min

   Place two bottom boards (140×776mm) side by side inside the box with a 5mm gap to improve drainage. Drill 4-6 holes of 8mm diameter centrally for drainage. Drill pilot holes then fix each spot with two 38mm coarse-thread screws to the side and front/back boards.

   Drill a hole

   下穴 φ3.5mm

   DrillSTEP 5 / 10

   Tip

   • Drain holes are essential to prevent soil saturation and root rot.
   • Leaving a 5mm slit between bottom boards improves drainage; insert chopsticks to keep spacing while fixing.
   • Laying pumice stone on the bottom helps prevent drain holes from clogging.

   Watch out

   • Forgetting drain holes causes plants to die.
   • Sealing bottom boards without gaps traps moisture and causes wood rot.
6. 6

   Right angle confirmation and surface preparation for painting

   ≈ 15 min

   Measure both diagonal lengths of the assembled box with a tape measure; confirm they differ by no more than 2mm. Correct any warping with clamps. Lightly sand the entire surface with #240 grit sandpaper and remove dust.

   Inspect

   No wobble ✓

   InspectSTEP 6 / 10

   Tip

   • Large diagonal difference may prevent pots from fitting; aim within 2mm.
   • Glue spots repel paint; sand them off.
   • Treat inside surfaces carefully as well.

   Watch out

   • Ignoring warping causes fitting failure in window frame.
   • Applying paint over dust causes rough surfaces.
7. 7

   First application of outdoor wood preservative

   ≈ 30 min

   Apply water-based outdoor wood preservative (such as Xyladecor or Osmo Color) with a brush over all surfaces (front, back, inside, outside, and board ends). Apply extra on board ends to soak in well. Let dry naturally for 2-3 hours.

   Paint

   Watco oil / varnish

   PaintSTEP 7 / 10

   Tip

   • Penetration into board ends is critical for preservative effect.
   • Water-based paints are easy to wash from brushes with water, ideal for beginners.
   • Painting inside protects wood from soil moisture.

   Watch out

   • Applying too thickly causes uneven drying and later peeling; two thin coats are recommended.
   • Do not paint if rain is forecast within drying time; paint may run.
8. 8

   Second coating

   ≈ 30 min

   Once first coat dries, gently buff the surface with #400 sandpaper before applying the second coat. Apply thinner than the first coat. Since this is for outdoor use, ensure a solid film formation. Allow over 24 hours drying for full curing.

   Paint

   Watco oil / varnish

   PaintSTEP 8 / 10

   Tip

   • Two coats greatly increase protection and are essential outdoors.
   • Light buffing (#400) is enough to smooth surface without removing first coat.
   • Keep coated item in dust-free area during drying.

   Watch out

   • Rain before full drying (24h) causes paint run.
   • Over-buffing may remove the first coat.
9. 9

   Attaching to the window frame

   ≈ 30 min

   Fix the box to the window frame using L-brackets or dedicated brackets. Secure brackets firmly into structural backing (wood frame or studs). After installation, gently shake the box to check for looseness.

   Fix to the wall

   Anchor to studs

   InstallSTEP 9 / 10

   Tip

   • Empty box is light, but weight with soil, water, and plants exceeds 10kg; use strong brackets.
   • Locate backing with a stud sensor before screwing.
   • Removable hanging brackets are convenient for watering and cleaning.

   Watch out

   • Exceeding bracket load capacity risks falling.
   • Gypsum board alone is insufficient; always anchor into framing.
10. 10

    Planting and final checks

    ≈ 25 min

    Line the inside with root barrier sheet or nonwoven fabric to prevent direct soil-wood contact. Spread 2cm of pumice stones, then add soil and plants. Water thoroughly and confirm drainage through drain holes. Observe daily for several days after installation.

    Done!

    Done — nice work!

    DoneSTEP 10 / 10

    Tip

    • Root barrier sheets extend wood life by 3-5 years; available at 100-yen shops.
    • Pumice stones prevent drain holes from clogging.
    • First watering should be generous to verify drainage.

    Watch out

    • Without root barrier, wood deteriorates from moisture.
    • Water dripping beneath should be caught with a tray to avoid staining walls.

Warnings

• ⚠️Wood preservative coating is essential for outdoor use (reapplication recommended once a year).
• ⚠️Use stainless screws (iron screws will rust).
• ⚠️Drill pilot holes before screwing to prevent splitting the wood.

Find more blueprints in this category or store