How to prepare a site for a raised garden bed

Mark the bed and its working space

Mark the widest assembled footprint, including corners, legs and any caster clearance. Mark paths separately, then walk the route with the tools or soil bags you intend to bring in. Check sunlight for your intended planting and the route from the water source. The path guide explains why a bed that fits the gap may leave too little working space.

Choose a stable, level position for the frame or legs. Check across both directions before filling and again after assembly; do not use extra soil inside the bed to disguise a rocking support or tilted frame. For a sloping site, use a maker-approved installation or get site-specific advice before excavating, building a retaining edge or improvising leg extensions.

Beds on garden soil: leave room for roots

Maryland Extension recommends testing the existing soil before amendments. Its site guidance distinguishes a productive garden from lawn and compacted ground. Clear vegetation where necessary and choose its no-dig or minimum-disturbance approach for the actual condition. There is no need to dig every site to the same depth.

An open bottom lets roots reach the soil below. Keep that path in mind before laying permanent fabric or plastic. Inspect where water goes after rain; bed height alone does not resolve drainage. Choose amendments from your soil findings, then use the mix calculator only to split the proportions you have chosen.

Compacted or uncertain soil: resolve drainage first

For compacted ground with little vegetation, Maryland describes clearing the site and rocking a garden fork through the footprint to loosen it without turning the soil over. If water still stands, the problem needs an answer before filling an open-bottom bed. A taller wall does not prove the ground beneath will drain.

Record what you know separately: surface condition, soil test, drainage observation and any history of dumped material or former structures. Uncertain fertility and suspected contamination are different questions. A routine nutrient test may not answer the latter.

If the soil may be contaminated

Pause the normal open-bottom setup when site history raises a contamination concern. Ask your local Extension service or appropriate soil laboratory what sampling and contaminant tests fit that history. Tell them the bed is intended for food growing if that is your plan.

Do not treat fresh soil, a taller bed, hardware cloth or landscape fabric as proof of isolation from contaminated ground. Decide the location, containment and handling with the relevant local guidance before purchasing fill. The calculator can describe a volume while that decision remains unresolved.

Concrete, patio, balcony or deck: plan containment and runoff

On an impermeable surface, roots cannot continue into native soil. Decide the required growing depth, a way to retain the mix and an outlet for drainage. Minnesota discusses permeable liners for hard-surface beds. Water and staining may still reach the surface beneath: identify the outlet and avoid directing runoff onto a walking route or neighboring property.

An elevated planter’s floor carries the mix; its drains must remain open. Follow its fill restrictions. For example, Gardener’s Supply elevated cedar planters specify potting mix and exclude ordinary garden soil and rocks. Check the exact selected model, including legs and casters.

For a deck, balcony, roof or other supported structure, get the actual support assessed before purchase. A planter’s own load rating is not the surface rating. Use the component record below to prepare for that conversation; no total or diagram here approves a structure.

Choose a liner or barrier for the job

A side liner separates the mix from a wall; it need not close the bottom. A permeable bottom liner can retain growing medium on a hard surface while allowing water to leave. Hardware cloth is a physical screen for burrowing animals, not a water barrier or contamination treatment. Confirm appropriate mesh and attachment for the local animal and bed.

A permanent bottom sheet over soil can change drainage or root access. Avoid an impermeable plastic floor as a universal default. Keep drains open on contained planters and follow the exact maker’s liner instructions. If the maker already supplies a liner or floor, identify what it does before adding another layer.

Before and after assembly

Lay out the exact configuration’s parts on the prepared site. Check the kit version, corner pieces, fasteners, braces, edge caps and any supplied liner against the manual. Resolve missing or damaged load-carrying parts before adding soil. Follow the manufacturer’s sequence for tightening and bracing; this checklist does not replace it.

Check that the assembled frame or legs sit steadily, that protective caps are fitted where required and that drains remain clear. Measure the widest outside footprint again, then measure the inside at the intended fill line. Transfer those separately to the garden plan. Use the inside dimensions for your soil order.

Prepare a filled-weight record for a support assessment

Record the exact planter and caster option, empty container weight, intended fill volume, growing-medium wet or saturated bulk density with its source, and separately supported accessories or stored items. Ask the assessor what water condition and load distribution they require. If a necessary weight is unknown, retain it as unknown.

For a consistent density basis, fill mass equals fill volume multiplied by that density. Do not add the same retained water twice when a saturated density already includes it. Give the assessor the number and positions of legs or wheels, the surface construction and the intended layout. A pounds-per-square-foot average can hide concentrated leg loads.

Print record: Planter/model ______; empty weight ______; fill volume ______; density and water basis ______; other loads ______; leg/wheel positions ______; support assessor and unresolved questions ______. Revisit material and construction if the support requirements change the choice.

References

• Growing Vegetables in Raised Beds, University of Maryland Extension
• Raised bed gardens, University of Minnesota Extension
• Raised Bed Gardening, Utah State University Extension