Good raised-bed soil is loose, deep, and crumbly: it holds water for roots but lets heavy rain drain through. University of Maryland Extension suggests should make up 25 to 50 percent of the bed by volume. Before buying anyg, look at what's under the bed. If the native soil drains and isn't badly compacted, loosen it with a garden fork and build on top of it; roots grow down into it, and you need less fill. Send a sample to a soil testing lab first, and ask for a lead test if you plan to grow food.
For a bed on soil, a blend of purchased topsoil and compost, at roughly 2 parts topsoil to 1 part compost or half and half, is the standard extension recommendation. Some suppliers sell topsoil already blended with compost. Topsoil quality varies widely and is not regulated in many places, so ask where it came from and for any test results. Good topsoil is dark and crumbly with an earthy smell. Turn down soil that smells foul, shows grayish mottling, or is very sandy, sticky, or chalky.
Bagged raised-bed mixes and organic s usually contain no actual mineral soil. They are blends of bark fines, wood waste, compost, and peat or coir. They work, and they make sense for small beds, containers, and beds on pavement, but they are expensive by volume for large beds and shrink as the organic matter breaks down. Peat and coir mixes repel water when dry, so wet them thoroughly before filling. For beds on a hard surface, use compost and soilless mix 1:1; topsoil can make up as much as 20 percent of the volume in beds at least 16 inches deep.
Deep beds take a lot of material. A 4-by-8-foot bed filled 12 inches deep holds about 32 cubic feet, more than a cubic yard, and the cost of bagged mix adds up fast. On soil, a bed doesn't need premium mix all the way down. Smother grass with cardboard covered by a few inches of compost, add loosened soil from the paths around the bed, and save the compost-rich blend for the upper layer. On pavement, depth matters more: about 8 inches for leafy greens, beans, and cucumbers, and 12 to 24 inches for tomatoes, peppers, and squash.
Every bed settles as organic matter breaks down, so plan to top it up rather than refill it. Each season before planting, spread 1 to 2 inches of compost over the surface and work it lightly into the top few inches with a fork. Avoid deep digging or tilling, which brings weed seeds to the surface. Retest the soil after the first year, once the materials have had time to mix and react, and adjust or nutrients based on the results rather than adding fertilizer by guesswork.
- TomatoThe warm-season anchor of the summer garden.
- PepperA tropical perennial grown as an annual — patient, slow, and particular about warmth.
- LettuceA cool-season leaf crop that thrives in spring and fall, sulks in summer heat.
- KaleThe cold-weather workhorse that improves when everything else quits.
- CucumberA thirsty vine that wants warm soil, steady water, and something to climb.
- MoleRaised surface tunnels and conical soil mounds across garden beds — moles tunnel for earthworms and grubs, not plant roots.
- Onion MaggotOnion seedlings and sets collapsing at the base, with white maggots tunneling into bulbs at or below the soil line.
- Root-Knot NematodeStunted, wilting plants with characteristic knobby galls on the roots. Worst in sandy soil and warm climates.
- SlugIrregular holes in low-growing plants overnight, with silver slime trails left behind on leaves and soil.
- Southern BlightWhite cottony mycelium and small round sclerotia at the stem base, with rapid plant collapse in warm, moist soil.
- When is the best time to add compost to the garden?Fall is often the best time to add compost to garden beds — it has all winter to incorporate and break down further, and beds are ready to plant without delay in spring.
- Should I use fertilizer or compost — what's the difference?Compost improves soil structure and feeds slowly over the long term; fertilizer delivers specific nutrients quickly — most productive gardens benefit from both, used for different purposes.
- How do I know if my soil is compacted, and what can I do about it?Compacted soil pools water after rain, resists a probe or screwdriver pushed by hand, and produces stunted plants with shallow root systems — the fix depends on severity and whether you're willing to leave soil undisturbed over time.
- My soil is heavy clay — can I actually grow vegetables in it?Yes, but clay soil needs amendment over time — raised beds with imported soil offer a faster path, while in-ground clay improvement with organic matter takes 2–3 seasons to become reliable.
- When and how should I adjust my soil pH, and how long does it take to work?pH amendments work slowly — lime often takes a few months and elemental sulfur several months to a year to shift pH — so apply them in fall or as far ahead of planting as you can, not at planting time, and retest before adding more.