Start with soil depth and spacing before you place anything in the ground

The depth of soil you need depends on what you are growing. Shallow-rooted plants like lettuce, spinach, and herbs need 6 to 8 inches. Medium-rooted crops like beets, chard, and bush beans need 8 to 12 inches. Deep-rooted plants like tomatoes, peppers, carrots, and potatoes need 12 inches or more. If your raised bed is only 8 inches deep, you can still grow shallow and medium-rooted plants, but you will not be able to grow root vegetables or large fruiting plants.

Before you plant anything, decide how many plants will fit. Crowding plants wastes space and creates humidity that invites disease. A general rule: space plants so their mature leaves will almost touch but not overlap. For tomatoes, that means one plant per 2 feet of bed length. For lettuce, space plants 6 to 8 inches apart. For peppers, allow 12 to 18 inches between plants. Check the seed packet or plant label for the specific spacing your variety needs.

Key Takeaways

  • Fill your raised bed with a mix of topsoil, compost, and peat moss or coconut coir in roughly equal parts, rather than garden soil alone, which compacts over time.
  • Plant seeds or transplants at the depth shown on the seed packet or plant label, not deeper, because seeds buried too far will not sprout.
  • Space plants according to their mature size so leaves do not overlap, which prevents air circulation and disease.
  • Water when ready after planting and keep the soil consistently moist but not waterlogged for the first two to three weeks while roots establish.

Fill the bed with the right soil mixture, not plain garden soil

Plain garden soil compacts in a raised bed and drains poorly. Instead, use a mixture: roughly one-third topsoil, one-third compost, and one-third peat moss or coconut coir. This combination holds moisture, drains well, and gives roots room to grow. If you are filling a 4-by-8-foot bed that is 12 inches deep, you will need about 32 cubic feet of soil mix, which is roughly 1 cubic yard. Most garden centers sell soil by the bag or by the cubic yard.

Fill the bed to within an inch of the top rim. The soil will settle over the first few weeks, so starting slightly high prevents you from ending up with a bed that is too shallow. Mix the soil with your hands or a shovel as you add it so the layers blend together rather than staying separate.

Plant seeds directly into the soil at the correct depth

Read the seed packet before you plant. It will tell you the planting depth, spacing, and days to germination. Plant seeds at the depth listed — usually between one-quarter inch and one inch deep. A seed planted too shallow will dry out. A seed planted too deep will not have enough energy to push through the soil to reach light.

Make a small furrow or hole with your finger or a stick at the depth the packet specifies. Drop the seed in, cover it gently with soil, and press down lightly so the seed makes contact with the soil. Do not pack it hard. Water gently with a mister or watering can so you do not wash the seed away. Keep the soil moist until the seed sprouts, which usually takes 5 to 14 days depending on the plant.

Transplant seedlings and nursery plants at the soil line

If you are planting seedlings you started indoors or bought from a nursery, plant them at the same depth they were growing in their original pot. The soil line on the stem is your guide — bury the plant up to that line, not deeper. The exception is tomatoes: they can be planted deeper than they were in the pot because they will develop roots along the buried stem, which makes them stronger.

Dig a hole slightly larger than the root ball. Gently remove the plant from its pot and loosen the roots with your fingers so they spread into the new soil rather than staying in a tight ball. Set the plant in the hole, fill around it with soil, and press gently so there are no air pockets. Water when ready after planting so the soil settles around the roots.

Water consistently for the first three weeks after planting

New plants and seeds need steady moisture while they establish roots. Check the soil daily by pushing your finger an inch into the surface. If it feels dry, water. If it feels moist, wait. The goal is soil that is consistently damp but not soggy — roots need oxygen, and waterlogged soil suffocates them.

Water in the early morning so foliage dries quickly and disease spores do not settle on wet leaves. Use a soaker hose or drip line if you have one, because they deliver water directly to the soil without wetting the leaves. If you use a watering can or sprinkler, water the base of the plant, not the top. After three weeks, most plants will have roots deep enough to handle dry spells between waterings, though you should still water during heat waves or drought.

Add mulch after plants are established to retain moisture and suppress weeds

Once seedlings are 3 to 4 inches tall or transplants have been in the bed for two weeks, add a 2-inch layer of mulch around them. Use straw, shredded leaves, or wood chips. Mulch keeps the soil cooler, reduces water loss, and prevents weeds from taking root. Keep mulch a few inches away from plant stems so it does not trap moisture against the stem and cause rot.

As the season goes on, mulch breaks down and becomes part of the soil. You can add more in mid-summer if the layer gets thin. By fall, the decomposed mulch will have added organic matter to your bed, which improves soil structure for next year.

Adjust spacing and thin seedlings if they are too close

If you planted seeds directly in the bed, they may sprout closer together than the spacing you need. Once seedlings have two true leaves (the second set of leaves that appear after the initial rounded seed leaves), thin them by removing the weaker plants. Pinch them off at soil level or pull them gently. Do not leave them lying on the soil — remove them from the bed so they do not rot and attract pests.

Thinning feels wasteful, but crowded plants compete for water and nutrients, and poor air circulation invites fungal disease. The plants you remove are small and not worth eating, so thinning is the right choice. Space the remaining seedlings according to the seed packet instructions.

Frequently Asked Questions

Can I plant in a raised bed in spring and fall, or just one season?

You can plant in both seasons. Spring planting starts after your last frost date, which varies by location. Fall planting happens 8 to 10 weeks before your first frost date so plants have time to mature before cold arrives. Cool-season crops like lettuce, spinach, and broccoli actually prefer fall planting because they grow better in cooler weather.

What if my raised bed soil is too wet to plant?

Wet soil compacts when you work it, which damages structure and makes it hard for roots to grow. Wait until the soil crumbles in your hand rather than forming a tight ball. If you are in a hurry, spread the soil in the sun for a day or two to dry it out, or add more compost or peat moss to improve drainage.

Do I need to add fertilizer when I plant?

If you mixed in compost when you filled the bed, you have enough nutrients for the first month or two. After that, most plants benefit from a light feeding every three to four weeks. Use a balanced fertilizer like 10-10-10, or add compost as a top dressing. Follow the package instructions for amounts.

How close can I plant different crops together?

Some plants grow well together and some do not. Tomatoes and basil are good companions. Tomatoes and brassicas like cabbage compete for nutrients. Lettuce and radishes can share space because radishes mature and are harvested before lettuce needs the room. Check a companion planting chart for your specific crops, or follow the spacing on the seed packet as a safe default.

Can I plant in the same spot every year, or do I need to rotate?

Rotating crops prevents soil depletion and reduces pest and disease buildup. If you grew tomatoes in one section this year, plant something from a different family there next year — lettuce, beans, or root vegetables instead. If you add compost each year, you can get away with less rotation, but some rotation is still better for long-term soil health.