The Importance of Plant Spacing
An adequate space between your plants will reduce competition for light, will conserve water, and will provide more soil nutrition to each plant.
There is a limit to the amount of nutrients in your soil. By leaving plenty of room between plants, they can have a wide area from which to draw their sustenance. Keeping the area weed-free will also allow more nutrients to be available for the plants you want to grow.
As plants grow, light will be reduced through the developing leaf canopy. This shade will slow plants down if plants are too crowded. Leaving more space between plants allows more sun and brighter light to hit expanding plants, and this will result in faster, more robust growth.
Unseen competition for root room can also slow plants down. Plants thrive when roots can freely spread in loose healthy soil. Roots will also draw more moisture if they have plenty of room.
General space recommendations for some crops
Beets – 1 foot
Broccoli, cauliflower, cabbage and kale – 4 feet
Carrots – 1 foot
Corn – 3 feet
Cucumbers – 5-6 feet
Lettuce – 2 feet
Peas – can be planted thickly
Peppers – 3 feet
Potatoes – 18 inches
Spinach – 1 foot
Squash – 8-10 feet
Tomatoes – give the roots the same amount of width as the leaves take above ground. Determinate varieties will need less room than indeterminates