Planning a 4 x 8 Raised Bed: How Many Plants Fit and Which Crops to Keep Apart
A 4 by 8 foot raised bed is the most common size sold as a kit, and for good reason: at 4 feet across you can reach the middle from either side without stepping on the soil, and at 8 feet long it fits most yards. It holds 32 square feet of growing space. That sounds like a lot until you try to fit tomatoes, herbs, salad and root crops into it at once.
This guide works through that problem with two of our tools. The Garden Layout Planner takes the bed size and two to six crops, splits the bed between them and lists which pairs are traditional companions and which are traditionally kept apart. The Plant Spacing Calculator takes one crop and one patch of ground and fits plants into rows. Used together they answer the two questions most people ask before they buy seedlings: how many of each, and what goes next to what.
Step 1: decide how many crops share the bed
The layout planner divides the bed area equally among the crops you tick. That one rule shapes everything else, so it is worth seeing what it does to a 4 x 8 bed:
| Crops chosen | Area each crop gets |
|---|---|
| 2 (tomato, basil) | 16 sq ft |
| 4 (tomato, basil, lettuce, carrot) | 8 sq ft |
| 5 (tomato, potato, cabbage, bean, onion) | 6.4 sq ft |
| 6 (tomato, pepper, basil, lettuce, carrot, onion) | 5.3 sq ft |
An equal split is a starting point, not a recommendation. A tomato plant needs far more room than a carrot, so a real plan usually gives the big crops more than their share. Treat the planner's output as a quick check of what the bed can hold, then adjust.
Step 2: the four-crop bed, worked through
Here is a classic summer mix: tomato, basil, lettuce and carrot in a bed 8 feet long and 4 feet wide. The layout planner gives each crop 8 square feet and returns these counts:
| Crop | Spacing the tool uses | Plants that fit | Area (sq ft) |
|---|---|---|---|
| Tomato | 24 in | 2 | 8 |
| Basil | 10 in | 11 | 8 |
| Lettuce | 10 in | 11 | 8 |
| Carrot | 3 in | 128 | 8 |
Under Good Companions it lists four pairs: tomato and basil, tomato and lettuce, tomato and carrot, and lettuce and carrot. Under Keep Apart it reports "No keep-apart pairs found in the companion table for these crops." All four crops have entries in that table, so here the empty list means none of them is on another's avoid list.
Two tomato plants is the figure most people find surprising. At 24 inches apart, a tomato claims 4 square feet, so an 8 square foot quarter holds two. If tomatoes are the main reason you built the bed, a two-crop plan of tomato and basil gives each 16 square feet and the planner returns 4 tomatoes and 23 basil plants. Nobody needs 23 basil plants, which is the point: the equal split is where you start adjusting, not where you stop.
Step 3: check the counts against real rows
The layout planner counts plants by area: it divides each crop's square feet by the square of its spacing and rounds down, and its results column is labelled "Plants That Fit (area-based estimate)" for that reason. That is a ceiling on what could fit, not a planting plan, because plants go in rows and a strip of ground rarely divides evenly.
To see the difference, run one quarter of the bed, a strip 2 feet long and 4 feet wide, through the Plant Spacing Calculator with square spacing:
| Crop | Layout planner (area method) | Spacing calculator (rows) |
|---|---|---|
| Tomato, 24 in | 2 | 2 (2 rows of 1) |
| Basil, 10 in | 11 | 8 (4 rows of 2) |
| Lettuce, 10 in | 11 | 8 (4 rows of 2) |
| Carrot, 3 in | 128 | 128 (16 rows of 8) |
Tomatoes and carrots agree. Basil and lettuce do not: 2 feet at 10 inch spacing holds only 2 plants per row, because a third would need 30 inches. The area method says 11; real rows give 8. Buy for the smaller number, or change the shape of the patch. The spacing calculator rounds down at every step (rows, then plants per row), so its answer is one you can actually lay out with a tape measure.
For the whole bed planted with one crop, the spacing calculator gives 8 tomatoes in 2 rows of 4, which is the most a 4 x 8 bed can hold at 24 inch spacing on a square grid.
Step 4: which crops to keep apart
The Keep Apart list comes from a short table of traditional pairings. Try a five-crop mix of tomato, potato, cabbage, bean and onion and the planner flags four pairs to separate:
- Tomato and potato
- Tomato and cabbage
- Cabbage and bean
- Bean and onion
It also lists four good pairs: tomato and onion, potato and cabbage, potato and bean, and cabbage and onion. When a pair appears on both lists in the table, the tool treats it as one to keep apart.
Some of these pairings have a practical reason behind them. Tomato and potato are in the same plant family and share diseases such as late blight, so growing them side by side gives a problem two hosts. Others are garden tradition with thinner evidence. Treat the list as a set of reminders worth considering, not as a guarantee that a good pair will raise your yield or that a bad pair will fail. Our guide to which pairs the layout planner flags goes through the table pair by pair.
In a 4 x 8 bed, keeping apart usually means opposite ends. Put the tomatoes at the north end so they do not shade the rest (in the Northern Hemisphere), and keep potatoes in a separate bed or container altogether.
Step 5: work out the soil before you buy plants
A bed that size needs a lot of soil. Using the Soil Volume Calculator for a rectangle 8 feet by 4 feet:
| Fill depth | Cubic feet | Cubic yards | 1.5 cu ft bags | 2 cu ft bags |
|---|---|---|---|---|
| 12 in | 32 | 1.185 | 22 | 16 |
| 10 in | 26.67 | 0.988 | 18 | 14 |
Bag counts are rounded up to whole bags. At more than a cubic yard, a bulk delivery is often worth pricing against bags. The guide to filling a raised bed covers mixes and settling in more detail.
A sample plan you can adjust
Putting the numbers together, here is one way to plant a 4 x 8 bed for summer that respects both tools:
- North 4 feet: 4 tomatoes at 24 inches (2 rows of 2), with basil tucked along the south edge of that half where it gets sun.
- Middle 2 feet: lettuce at 10 inches, 8 plants in 4 rows of 2, sown or planted early and cleared before the tomatoes shade it out.
- South 2 feet: carrots at 3 inches, up to 128 in 16 short rows, thinned to that spacing after they come up.
Run your own version through the planner and the spacing calculator, then write the counts on your shopping list before you go to the nursery.
What these tools do not cover
- Height and shade. Neither tool knows that a staked tomato will shade lettuce on its north side. Check the bed's sun with the Sunlight Requirements Guide and put tall crops where their shadow falls outside the bed.
- Timing. Lettuce and carrots can go in weeks before tomatoes. The counts assume everything shares the bed at once; staggering plantings lets you use the same space twice.
- Varieties. Spacing is one figure per crop. A compact patio tomato and a sprawling indeterminate one need different room; the seed packet or plant label wins.
- Paths and supports. Cages, stakes and the strip you need to reach in are not subtracted.
Building the bed safely
For a food bed, avoid old railroad ties and timber treated with CCA (chromated copper arsenate), which was phased out of residential use but still turns up in reclaimed lumber, and do not use wood with old paint that may contain lead. Untreated cedar or modern treated lumber rated for ground contact are common choices; check the label. If you are filling with soil dug from near an older house, a soil test for lead is worth doing before you grow food in it. Bags of soil are heavy, so lift with your legs and split loads. If any part of the project involves digging deeper than a few inches into the ground, call your utility-locate service first (811 in the US) so buried lines are marked. Wear gloves when handling soil and compost, and keep your tetanus vaccination up to date.