Lasagna gardening is a no-dig method of filling a bed with layers of organic material that break down into rich soil, and it suits a raised bed perfectly. You lay cardboard on the bottom to smother weeds, then alternate layers of brown material with green material, the same balance a compost pile needs. The browns and greens decompose together and fill the bed with fertile soil over time. The method fills a bed cheaply using yard and kitchen waste, and it skips the cost of buying bagged soil to fill the whole frame.
The first lasagna bed I built was an experiment born out of being short on money and long on fallen leaves. I had a new frame to fill and no budget for a yard of soil, so I packed it with autumn leaves, grass clippings I had saved, kitchen scraps, and a few wheelbarrows of half-finished compost, all stacked over a base of flattened cardboard boxes. By spring the pile had settled into dark, crumbly soil, and the tomatoes I planted in it that year were among the best I have grown. It cost me almost nothing but time.
Why lasagna layering suits a raised bed
A raised bed gives you a contained frame to build the layers in, which keeps the materials neat and stops them spreading. The frame holds the pile in shape while it breaks down, and the defined sides make it easy to fill in even layers. You are building a compost pile inside the bed, and the bed keeps it tidy.
The biggest reason to use this method is cost. Filling a deep raised bed with bought soil and compost is the most expensive part of building one, often costing more than the frame itself. A 4 by 8 foot (1.2 by 2.4 m) bed 12 inches (30 cm) deep holds about 32 cubic feet (0.9 cubic meters), which is 30 to 40 wheelbarrow loads. Lasagna layering fills the bed with materials you already have or can get free: fallen leaves, grass clippings, kitchen scraps, cardboard, and shredded paper. Instead of buying a yard of soil, you turn your yard and kitchen waste into the soil.
It is also a no-dig method, which means no breaking ground or turning soil. You build up rather than dig down, layering the materials on top of whatever is below, even grass or weeds. The cardboard base smothers what is underneath, so you do not have to clear the ground first.
Understand browns and greens
The method works on the same principle as a compost pile, balancing carbon-rich brown material against nitrogen-rich green material. Get the balance roughly right and the layers break down into good soil. Get it badly wrong and the pile either sits inert or turns into a slimy, smelly mess.
Browns are the carbon-rich, dry, woody materials: fallen leaves, straw, shredded paper, cardboard, and dry plant stems. They are the bulk of the pile and provide the structure and carbon that the decomposing organisms need. Browns have a carbon-to-nitrogen ratio of about 30:1 to 80:1 depending on the material, and they break down slowly.
Greens are the nitrogen-rich, wet, fresh materials: grass clippings, vegetable and fruit scraps, fresh garden trimmings, coffee grounds, and finished compost. They feed the organisms that break everything down and provide the nitrogen. Greens typically have a carbon-to-nitrogen ratio of about 15:1 to 25:1.
Aim for roughly 2 parts brown to 1 part green by volume. Too much green makes the pile wet, smelly, and slimy. Too much brown makes it dry and slow to break down. The two-to-one ratio gives you a pile that decomposes steadily into rich, dark soil.
Get the materials together
The materials are the part to plan ahead for, because you need a fair amount to fill a bed. The single best time to build a lasagna bed is fall, when leaves and spent garden plants are plentiful. A pile of fallen leaves gives you all the brown material you need, and end-of-season garden waste adds greens.
Save grass clippings through the season, collect kitchen scraps, and break down cardboard boxes for the base and the brown layers. Shredded office paper and newspaper work as browns too. If you garden where you can get free wood chips, leaf mold, or aged manure, these add to the mix. The point is to use what you can gather rather than buy, so collect materials over weeks rather than trying to fill a bed in a single afternoon.
A 4 by 8 foot (1.2 by 2.4 m) bed 12 inches (30 cm) deep needs about 18 to 24 cubic feet (500 to 680 L) of loose browns and 9 to 12 cubic feet (250 to 340 L) of loose greens before settling. That is roughly 8 to 10 large paper leaf bags of dry leaves and 4 to 5 contractor bags of grass clippings, give or take. The actual amounts depend on how much the materials compact when you pile them.
Avoid materials that bring problems: meat, dairy, and oily food scraps attract pests and smell as they rot, and weeds gone to seed can sprout in the finished bed. Diseased plants and anything treated with herbicide should also stay out, since the herbicide can persist and harm your crops.
Lasagna layer materials at a glance
| Material | Type | Layer depth | Notes |
|---|---|---|---|
| Dry autumn leaves | Brown | 4-6 in (10-15 cm) | Best bulk brown; oak leaves break down slowly, maple faster |
| Straw (not hay) | Brown | 4-6 in (10-15 cm) | Adds structure; avoid hay which carries weed seeds |
| Shredded newspaper / office paper | Brown | 2-3 in (5-8 cm) | Tear or shred first; avoid glossy inserts |
| Corrugated cardboard | Brown | Single layer base | Remove tape and labels; wet down well |
| Grass clippings (fresh) | Green | 2-3 in (5-8 cm) | Layer thinly; thick mats turn anaerobic |
| Vegetable kitchen scraps | Green | 1-2 in (2.5-5 cm) | Bury in browns to avoid pests |
| Coffee grounds | Green | Sprinkle 1/2 in (1.3 cm) | Slightly acidic; mix well into brown layer |
| Fresh / finished compost | Green | 2-3 in (5-8 cm) | Jump-starts microbial activity in the pile |
Build in fall for the best result
The ideal way to build a lasagna bed is in fall, then let it mellow over 4 to 6 months of winter. The layers break down slowly through the cold months, settling and composting into rich soil, and by spring the bed is ready to plant. Building in fall also lines up with the season when leaves and garden waste are most plentiful, so the materials are right there.
A fall-built bed will settle 30 to 50 percent in volume over winter as the materials break down and compress, so build it mounded 4 to 6 inches (10 to 15 cm) above the top of the frame, knowing it will sink. What looks like an overfull bed in October will be a settled, level bed by April.
Fall builds also avoid the issue of unfinished materials touching plant roots. By spring, the lower layers have had 4 to 6 months of slow decomposition, and any phytotoxins from half-rotted greens have broken down into plant-available nutrients. Carrots, lettuce, and other fine-seeded crops that would struggle in a fresh spring build germinate well in a fall-built bed that has settled.
Building in spring instead
You can build a lasagna bed in spring and plant it the same season, but it needs one adjustment. The lower layers will not have broken down yet, so top the bed with 3 to 4 inches (7.5 to 10 cm) of finished compost or screened topsoil and plant into that. The roots grow in the finished top layer while the layers beneath continue decomposing and feeding the bed through the season.
This works well for transplants and larger seeds planted into the top compost layer. Fine seeds sown directly are trickier, because the surface of a fresh lasagna bed is uneven as it settles. For a spring build, plant tomatoes, peppers, squash, beans, and other transplants or large seeds into the finished top layer, and the bed grows them well while it composts underneath.
The one thing that slowed my early lasagna beds was letting them dry out. A dry pile barely breaks down, because the organisms that do the composting need moisture to work. The first bed I built in a dry spell sat almost unchanged for weeks until I soaked it thoroughly, after which it broke down fast. Water each layer as you build, aim for the dampness of a wrung-out sponge, and check the bed through dry weather. A damp lasagna bed turns into soil in 4 to 6 months. A dry one just sits there for a year. Patience and moisture are the two things the method asks of you.
Fix a bed that is not breaking down
If a lasagna bed sits unchanged for weeks rather than turning into soil, the problem is almost always one of three things, and each has a simple fix. A dry pile barely decomposes, because the organisms doing the work need moisture, so soak the bed thoroughly and keep it damp. This is the most common cause and the easiest to put right.
Too much brown material and not enough green slows the bed down, because the decomposers lack the nitrogen they need. Add a layer of green material, like grass clippings or fresh compost, and water it in to get things moving. The opposite problem, too much green, makes the bed wet, slimy, and smelly, and the fix there is to mix in more brown material to soak up the excess and restore the balance.
Cold weather also slows decomposition, which is why a fall-built bed breaks down over the whole winter rather than in a few weeks. That is normal and expected, so give a fall bed time. If you need soil faster, build in warmer weather and keep the bed damp, and the layers break down far quicker.
What you end up with
A lasagna bed gives you soil built from the materials of your own yard and kitchen, which is satisfying as well as cheap. The finished soil is dark, crumbly, and rich in organic matter, the kind of soil that holds moisture, drains well, and grows healthy plants. Because it is full of decomposed organic matter and the life that comes with it, it tends to grow vigorous crops, especially heavy feeders like tomatoes and squash.
The bed continues to improve as the lower layers finish breaking down, and the soil level will keep dropping over the first season or two as everything composts fully. Top up with more compost or another round of layers each fall to replace what settles and what the crops use. Built and maintained this way, a lasagna raised bed gives you good soil for years from waste you would otherwise throw away.
Sources: Cornell University Garden-Based Learning, composting curriculum; Clemson Cooperative Extension, HGIC 1600 Composting.