Leaving abundant space in a flower bed or vegetable garden It is not very useful: weeds will quickly move into any open space. Instead, you should try to plant so that all the space is filled with greenery, yet while leaving enough room for the plants to reach their full size. That means each plant needs to touch its neighbors on all sides, yet still have enough room for healthy growth.
That’s why a laidback gardener should plant a bit tightly, at about three quarters of the plant’s mature size.
Thus, a perennial that reaches 30 inches (75 cm) in diameter at maturity could be planted with about 24 inches (60 cm) spacing in mind (this isn’t rocket science: round up or down a bit as needed). And a shrub that will attain 4 feet (120 cm) in diameter could be grown using 3 feet (90 cm) as its ideal spacing. Soon your flowerbed will be 100% full… but not overcrowded: your plants will still have the space they need to develop.
Do the same in the vegetable garden. Leaving a wide inter-row between each row of vegetables, as is done in the traditional vegetable garden, is an outright invitation to weeds. It’s like saying: come on in, I left you plenty of space! Instead, when you read the seed packet for vegetable X and it says to leave 6 inches (15 cm) between the plants and 16 inches (40 cm) between the rows, just ignore the second number. Plant at 6 inches (15 cm) between plants and between the rows, only leaving an inter-row (an empty row you can walk in) only about every 4 feet (120 cm) to give you access to the garden. And mulch that inter-row abundantly to make it as inaccessible as possible to weeds.
When you sow or plant your plants so they’re just a bit tightly spaced, the plants will be happy and you will be happy. It is only the weeds that will be upset!