Raised bed soil, drainage & lining FAQ
By Chen Wang · Senior Editor
Published August 3, 2026
Raised bed soil questions come up constantly once the frame is actually in the ground — what goes on the bottom, what mix to fill it with, and how much you’ll actually need to buy. These are the real questions gardeners search for most, answered directly.
Lining and the bottom of the bed
Whether you need a liner depends on what’s underneath the bed. On grass or weedy ground, a layer of plain cardboard or a permeable DeWitt Sunbelt Weed Barrier FabricCheck on Amazon → stops growth from pushing up into your soil while still letting water pass through. If the goal is keeping out burrowing pests rather than weeds, a metal liner does a better job than fabric, since rodents can chew through cloth. For a bed already sized to a specific footprint, a fitted liner like the Wshxjzyay Raised Garden Bed LinerCheck on Amazon → keeps soil contained and drains cleanly without extra cutting.
Most raised bed kits, including open-bottom galvanized designs, don’t need drilled drainage holes at all — the open bottom drains straight into native soil. Solid-bottom planters are the exception; those need holes or a gravel layer, since a planter with no drainage path just holds water at the roots until they rot.
Building the right soil mix
Skip straight topsoil and skip straight compost — both cause problems over a full growing season on their own. The standard is a blend, and there are two commonly cited ratios worth knowing: the 70/30 rule (roughly 70% mineral-based soil to 30% compost by volume) for a leaner, well-draining mix, and the heavier 5-4-3-2-1 recipe (topsoil, compost, peat or coir, coarse sand, and aged manure) for beds growing demanding crops like tomatoes. For a straightforward starting point, a reference guide like Raised-Bed Gardening for BeginnersCheck on Amazon → walks through building a first mix without overcomplicating it, and The First-Time Gardener: Raised Bed GardeningCheck on Amazon → covers the same ground with more step-by-step detail for a first bed.
Compost matters as much as the base soil. Use fully finished, dark, crumbly compost — fresh or unfinished compost can burn young roots. If you want to build your own supply instead of buying it, an inground worm composterCheck on Amazon → lets you bury kitchen scraps directly in an unused corner of the bed, or use a second worm composterCheck on Amazon → in a different bed to keep two composting sites running at once.
How much soil you actually need
For a standard 4x8-foot, 11-inch-deep bed — the same footprint as a FOYUEE Galvanized Raised Garden Bed (8x4x1ft)Check on Amazon → — plan on roughly 29 cubic feet of mix, which works out to about 19-20 standard 1.5 cubic foot bags. A 40 lb bag typically holds closer to 0.75 cubic feet, so it covers far less volume than gardeners expect. Buying soil in bulk by the cubic yard from a landscape supplier is almost always cheaper than bagged soil once you’re filling a bed this size.
Filling on a budget
To cut costs without cutting corners, bulk out the lower half of a deep bed with free material — cardboard, fallen leaves, small branches, or untreated wood chips — then reserve purchased soil and compost for the top 6-8 inches where roots actually grow. For beds you’re filling temporarily or in smaller sections, heavy-duty fabric grow bagsCheck on Amazon → are a cheap way to test a planting area before committing soil to a full-size frame.
The most common mistake isn’t any single ingredient — it’s skipping the blend entirely, packing soil down instead of leaving it loose, or never replenishing organic matter as it breaks down and the bed level drops each season.
Frequently Asked Questions
Are you supposed to line a raised garden bed?
Lining is optional but recommended if your bed sits on grass, weeds, or compacted soil. A permeable landscape fabric or weed barrier stops grass and weeds from growing up into the bed while still letting water drain through. If the bed sits on a hard surface like a patio or deck, skip the fabric and add a drainage layer instead.
Do I need to drill holes in the bottom of my raised garden bed?
Only if the bed has a solid bottom. Most raised garden beds, including open-bottom metal kits, are designed without a floor so water drains straight into the ground below. If you built a bed with a solid wood or plastic base, drill several 1/2-inch holes every 12-18 inches so water doesn't pool around the roots.
What happens if a planter doesn't have a drainage hole?
Water collects at the bottom instead of draining away, which saturates the soil, starves roots of oxygen, and leads to root rot within days for most vegetables. If you're using a solid-bottom planter, add drainage holes or a thick gravel layer before filling it with soil.
Should I line the bottom of my raised bed with cardboard?
Plain, uncoated cardboard is a common and effective first layer for a new raised bed. It smothers grass and weeds underneath, then breaks down within a season, feeding the soil above it. Remove tape and glossy labels first, since those don't decompose.
What is the best thing to line a raised bed with?
For weed suppression, a permeable woven landscape fabric is the standard choice because it blocks weeds without trapping water. For pest control against burrowing animals, a metal hardware cloth liner on the bottom works better since rodents can chew through fabric.
What do you put in the bottom of a raised bed garden?
For beds deeper than 12 inches, many gardeners add a bottom layer of coarse material like small branches, straw, or untreated wood chips before topping with soil. This is sometimes called hugelkultur, and it reduces how much soil mix you need while improving drainage as the material breaks down.
What should you use for the bottom of a raised bed garden?
If drainage is your main concern, leave the bottom open to native soil. If you're worried about grass or weeds coming through, add a layer of cardboard or landscape fabric first, then fill with your soil mix on top.
Can you use regular potting soil in a raised bed?
Potting soil alone works but gets expensive fast for anything larger than a small bed, and it can compact or hold too much moisture over a full season. Most gardeners blend potting soil or topsoil with compost, roughly two-thirds soil to one-third compost, for better long-term structure and drainage.
What kind of soil should I use in a raised garden bed?
A blended mix works best: roughly 50-60% high-quality topsoil, 30-40% compost, and a small amount of coarse material like perlite or coarse sand for drainage. Avoid pure garden soil dug from the ground, since it compacts heavily once confined in a raised frame.
What is the best soil to use for raised garden beds for vegetables?
Vegetables need loose, well-draining soil rich in organic matter. A mix of topsoil, aged compost, and a smaller share of aeration material like perlite or coarse sand gives roots the balance of nutrients, moisture retention, and airflow they need.
What soil will I need to fill my raised veggie bed with?
Plan on a blended mix rather than straight topsoil or straight compost. A common ratio is 50% topsoil, 30% compost, and 20% aeration material such as perlite, coco coir, or coarse sand.
What is the best compost to put in a raised bed?
Well-aged compost that's fully broken down and dark, crumbly, and earthy-smelling is ideal. Mushroom compost, aged manure compost, and quality bagged garden compost all work well; avoid fresh manure or unfinished compost, which can burn young roots.
Should I fill my raised bed with topsoil or compost?
Use both, not just one. Straight topsoil compacts and lacks nutrients over time, while straight compost holds too much moisture and breaks down too fast. A blend of roughly 60-70% topsoil to 30-40% compost gives you structure plus fertility.
Can I compost directly in my raised garden bed?
Yes, this is called in-bed or trench composting. Dig a hole or trench in an unused section of the bed, bury kitchen scraps and yard waste, and cover with soil. An inground worm composter makes this easier by containing the material while worms and microbes break it down in place.
What is the 70/30 rule in gardening?
The 70/30 rule is a soil-mix guideline: roughly 70% mineral-based material like topsoil or a soilless base, and 30% organic matter like compost. It's a simple ratio for building a raised bed mix that drains well but still holds enough nutrients and moisture for vegetables.
What is the 5-4-3-2-1 gardening method?
The 5-4-3-2-1 method is a simple raised-bed soil recipe by volume: roughly 5 parts topsoil, 4 parts compost, 3 parts peat moss or coco coir, 2 parts coarse sand or perlite, and 1 part aged manure. It's a heavier, richer mix than the leaner 70/30 blend, aimed at beds growing hungry vegetables like tomatoes and squash.
How many bags of soil do I need for a 4x8 raised bed?
A standard 4x8-foot bed that's 11 inches deep holds about 29 cubic feet of soil. Most bagged soil comes in 1.5 cubic foot bags, so you'd need roughly 19-20 bags. Buying soil in bulk by the cubic yard is usually cheaper once you're filling a bed this size.
How much will a 40 lb bag of soil cover?
A 40 lb bag of garden soil is typically close to 0.75 cubic feet. In a raised bed, that covers about 9 square feet at a 1-inch depth, or roughly 1 square foot at a full 8-9 inch fill depth. Always check the bag label, since density and bag volume vary by brand.
How to fill a raised garden bed cheaply?
Layer the bottom with free bulky material like cardboard, fallen leaves, small branches, or untreated wood chips to take up volume, then top it off with a thinner layer of purchased soil and compost for the top 6-8 inches where roots actively grow. Buying soil in bulk by the yard from a landscape supplier is also far cheaper per cubic foot than bagged soil.
What are common raised bed soil mistakes?
The most common mistakes are using straight topsoil or straight compost instead of a blend, skipping drainage entirely on a solid-bottom bed, packing the soil down instead of leaving it loose, and not replenishing organic matter each season as it breaks down and settles.
