Grow a Garden Calculator

Plant spacing is one of the most important decisions you make when planning a garden, and getting it right can be the difference between a productive harvest and a tangled, disease-prone mess. The classic square foot gardening method, popularized by Mel Bartholomew in the 1970s, divides the garden bed into one-foot-square sections and assigns each section a set number of plants based on their mature size. Tomatoes, for instance, need one plant per square foot, while you can fit sixteen carrots or nine spinach plants into the same area. This systematic approach maximizes yield per square foot while keeping pathways narrow and maintenance easy.

There are two distinct spacing measurements to keep in mind: in-row spacing (the distance between plants within the same row) and between-row spacing (the distance between rows themselves). In-row spacing is driven primarily by the plant's mature canopy width, while between-row spacing is often set wider to accommodate foot traffic, irrigation equipment, and proper air circulation. For most home gardeners, between-row spacing of 18–24 inches allows comfortable access without compacting the soil adjacent to plant roots.

Proper spacing dramatically affects yield in two competing ways. Overcrowding can increase total plant count but forces each plant to compete for light, water, and nutrients, reducing individual fruit size and overall quality. Undercrowding wastes space and can allow weeds to establish between plants before the canopy closes in to suppress them. The ideal spacing achieves full canopy closure at the plant's mature size — creating a living mulch that shades out weeds while allowing each plant maximum resources.

Air circulation is a powerful disease-prevention tool that gardeners often underestimate. Fungal diseases like powdery mildew, early blight on tomatoes, and gray mold on strawberries all thrive in humid, stagnant air pockets between densely planted leaves. Spacing plants so that breezes can move freely through the garden reduces leaf wetness time after rain or irrigation, which is the primary driver of fungal infection. A single additional inch of spacing can make a measurable difference in disease pressure over a growing season.

Companion planting adds another dimension to spacing decisions. Tall crops like corn can shelter heat-sensitive lettuce from afternoon sun. Nitrogen-fixing legumes like beans planted between heavy feeders like squash can reduce fertilizer needs. Aromatic herbs like basil near tomatoes may confuse pest insects searching for host plants by scent. When planning companion combinations, consider each plant's light requirements, root depth, and mature size to avoid inadvertent shading or root competition.

The choice between raised beds and in-ground gardens shapes everything from soil management to drainage to long-term maintenance cost. Raised beds — frames filled with custom soil mix and elevated 6–12 inches above grade — offer exceptional drainage, earlier spring warming, and complete control over soil composition. They also create a physical barrier that reduces weed intrusion and makes it easier to install row covers or netting for pest control. The main trade-off is upfront cost: lumber, hardware cloth (to exclude burrowing rodents), soil, and compost can add up quickly for large garden areas.

In-ground gardens require more soil amendment work initially but eliminate the material cost of raised bed frames. The key is improving native soil over multiple seasons with generous organic matter additions. A double-dig method — loosening soil to 18–24 inches deep and incorporating compost — creates the deep, friable root zone that most vegetables need. Heavy clay soils benefit enormously from gypsum and compost; sandy soils improve with compost and cover cropping.

Soil depth requirements vary significantly by crop. Shallow-rooted crops like lettuce, radishes, and herbs thrive in just 6–8 inches of quality soil, making them ideal for container gardening or thin raised beds. Medium-rooted crops — tomatoes, peppers, beans — need 12–18 inches. Deep-rooted vegetables like carrots, parsnips, and beets require at least 18–24 inches of loose, rock-free soil to form straight, full-sized roots. Compacted subsoil causes forked, stunted root crops regardless of surface fertility.

Soil pH profoundly affects nutrient availability. Most vegetables grow best between pH 6.0 and 7.0, where phosphorus, calcium, magnesium, and micronutrients like iron and manganese are maximally soluble. Acidic soils below pH 5.5 lock up phosphorus and can release toxic levels of aluminum; alkaline soils above pH 7.5 cause iron and manganese deficiencies visible as yellowing between leaf veins. A simple home pH test kit or extension service soil test will tell you whether to add lime (to raise pH) or sulfur (to lower pH) before planting.

Compost is the single most valuable soil amendment available to home gardeners, simultaneously improving drainage in clay, water retention in sand, microbial activity, and slow-release fertility. Aim to incorporate 2–4 inches of finished compost into the top 8–12 inches of soil each season, and top-dress around established plants as a mulch. For watering, drip irrigation or soaker hoses placed at the root zone reduce foliar disease, minimize water waste to evaporation, and allow flexible scheduling with simple timers — a significant upgrade from overhead sprinklers for any serious garden.