Before You Buy Plants: Measure Sun, Space and Soil First
A nursery in spring is designed to make you buy on impulse: trays of tomatoes, peppers and flowers in full bloom, all looking as though they would thrive anywhere. Most of the plants that fail in home gardens fail because of where they were put, not how they were cared for. A pepper in three hours of sun, twelve plants crammed into room for six, a bed filled with half the soil it needed: each of these is decided before the first plant goes in.
Three measurements prevent most of it: how much direct sun the spot gets, how much space you have, and how much soil it takes to fill. Each one has a GardenStuffs tool. Start with the Sunlight Requirements Guide, then the Plant Spacing Calculator, then the Soil Volume Calculator. Do them in that order, because sun decides what you can grow, space decides how many, and soil decides what you need to buy before any of it.
1. Sun: count hours of direct light
Plant labels say "full sun" or "part shade" without telling you what those mean in hours. The Sunlight Requirements Guide uses the common thresholds: enter the hours of direct sun a spot gets on a typical day and it returns a category and plants suited to it.
| Direct sun | Category | Examples the tool suggests |
|---|---|---|
| 6 hours or more | Full Sun | Tomato, pepper, squash, cucumber, bean, corn, sunflower, lavender, rosemary, marigold |
| 4 to under 6 | Partial Sun | Lettuce, carrot, beet, pea, broccoli, cabbage, spinach, parsley |
| 2 to under 4 | Partial Shade | Kale, chard, arugula, mint, cilantro, radish, leaf lettuce, hosta |
| Under 2 | Full Shade | Hosta, fern, astilbe, coleus, begonia, impatiens, lily of the valley |
Entering 7 hours returns Full Sun; 5 hours returns Partial Sun; 3 hours returns Partial Shade. Exactly 6 counts as Full Sun and exactly 4 as Partial Sun. The tool caps any figure above 14 hours at 14, since direct sun rarely lasts longer than that, and tells you when it has done so.
The hard part is the measurement, not the lookup. Watch the spot through one clear day, or check it every hour on a weekend, and note when it is in direct sun rather than bright shade. Our guide to measuring hours of direct sun walks through it, including how the count changes between spring and midsummer as the sun climbs and trees leaf out.
If the spot gets 3 hours, no amount of care will make tomatoes and peppers crop well there. That is the most useful thing to know before you shop. The good news is that leafy greens and many herbs do fine in partial sun and partial shade, and our guide to vegetables for partial shade covers what to grow instead.
2. Space: count plants, not trays
Once you know what will grow, work out how many fit. Measure the bed or border in feet and enter the length, width and crop in the Plant Spacing Calculator. Take a bed 10 feet long and 4 feet wide in full sun:
| Crop (spacing) | Pattern | Rows x per row | Total |
|---|---|---|---|
| Pepper (18 in) | Square | 2 x 6 | 12 |
| Pepper (18 in) | Triangular | 3 x 6 | 18 |
| Lettuce (10 in) | Square | 4 x 12 | 48 |
The triangular (offset) pattern fits a third row of peppers here because offset rows sit closer together; our guide to square and triangular spacing explains when that works. Either way, the count tells you something a six-pack label does not: a 10 x 4 bed of peppers wants 12 to 18 plants, not "a few trays".
If the bed will hold several crops, the Garden Layout Planner divides it between two to six crops and flags pairs traditionally kept apart. Its counts are an area-based estimate (the page labels them that way), so check each crop's patch in the spacing calculator before you buy.
3. Soil: work out the volume before the plants
A new bed, or a tired one that has sunk over a few seasons, needs soil, and it is usually more than people expect. The Soil Volume Calculator takes a rectangle or a circle, a depth in inches and a material label, and returns cubic feet, cubic yards and the number of 1, 1.5 and 2 cubic foot bags.
| Bed | Depth | Cubic feet | Cubic yards | 1 / 1.5 / 2 cu ft bags |
|---|---|---|---|---|
| 10 x 4 ft rectangle | 8 in | 26.67 | 0.988 | 27 / 18 / 14 |
| 4 ft round bed | 8 in | 8.38 | 0.31 | 9 / 6 / 5 |
The material choice (topsoil, compost, mulch or potting mix) is a label: the volume is the same whichever you pick, because it is the space you are filling. Bag counts are rounded up, so you will have a little left over. Close to a cubic yard, compare the price of bulk delivery with bags. Our guide to filling a raised bed covers mixes and settling.
Before you add anything to existing ground, a basic soil test is worth having. It tells you pH and nutrient levels, and whether you need fertilizer at all. If you do, the Fertilizer Calculator turns a bed area and the numbers on a bag into an amount, and the bag's label and your soil test win over its estimate.
Putting it together: a shopping list
With all three measurements, a shopping list writes itself. For the 10 x 4 bed in 7 hours of sun:
- Soil: 14 bags of 2 cubic feet (or about a cubic yard delivered) to fill to 8 inches.
- Plants: 12 peppers on a square grid, or plan half the bed for peppers and half for lettuce and run each half separately.
- Extras: stakes for peppers, and mulch for the surface once the plants are in.
Take the list to the nursery and buy what is on it. The trays that are not on the list are for another bed or another year.
What these tools do not cover
- Measuring the sun. The Sunlight Requirements Guide categorizes the hours you enter; it does not measure your garden or account for heat. Six hours of afternoon sun in a hot climate is harsher than six hours of morning sun in a cool one.
- Drainage. None of the tools tests drainage. A spot where water stands for a day after rain needs raising or a different plant, whatever its sun and size.
- Soil quality. The soil calculator gives volume, not what is in the soil. A soil test does that.
- Varieties and mature size. Spacing is one figure per crop; a plant label for a large variety may ask for more.
Safety before you dig and plant
- Call before you dig. If preparing a bed means digging deeper than a few inches, call your utility-locate service first (811 in the US) so buried gas, water and electric lines are marked.
- Check old soil and old wood. Soil next to older houses can contain lead from old paint; test it before growing food there. Do not build food beds from old railroad ties, CCA-treated timber or painted wood of unknown age.
- Know which plants are toxic. Several common ornamentals are poisonous to children and pets, including lily of the valley (on the shade list above), foxglove, oleander and yew, and true lilies are dangerous to cats. Check before planting them where children play or pets roam, and never eat any plant you have not positively identified.
- Lift and handle safely. Bagged soil is heavy; use a cart, lift with your legs, and wear gloves when handling soil, compost and fertilizer.