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 each vegetable can be found on these information pages.
Even More Space
In Steve Solomon’s book Water Wise Vegetables, he tells us that allocating more elbow room allows vegetables to get larger and yield longer and allows the gardener to reduce the frequency of irrigation.
Solomon contends that “Though hot baking sun and wind can desiccate the few inches of surface soil, if we dig down 6 inches or so, there is almost as much water present in September as there was in April.” Plants will withdraw moisture from greater depths when there is no moisture at the surface.
Reduced plant density is the key to dry gardening. Some of Solomon’s space recommendations are based on gardens in Western Oregon, and are as follows:
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.
Solomon also says “If plants with enough elbow room stop growing in summer and begin to appear gnarly, it is just as likely due to lack of nutrition as lack of water.” So nutrient-rich soil will increase the chances of success when dry gardening.
So leave your plants plenty of room for greater vegetable garden success.