For my raised bed gardens I am having difficulty with the plant spacing recommendations given on packets of vegetable seeds. The 12 to 18-inch row spacing recommended for most of the smaller plants seems to be the space required for us humans to plant, weed and harvest the gardens rather than what the plants require for maximum productivity.
Plants need space for the roots to spread out and room for the tops to collect sunlight. Any light that hits bare soil is wasted and encourages weeds to grow.
I would like to have plant spacing requirements given in square inches per plant or plants per square foot so I could plant according to plant requirements. I will provide spacing for my own needs as I see fit. I typically plant a 12-inch wide row and leave 1.5 feet for my cultivator.
I couldn’t find any university research on this topic but lucky for us, I found a book called "Square Foot Gardening" by Mel Bartholomew. He gives recommendations for how many seeds to plant per square foot in a raised bed garden. It is a good thing, because if we spaced our raised bed garden in 18-inch rows, we would not be very productive.
Mel’s book simplifies gardening by telling how to space plants. Extra-large plants like broccoli, cabbage and peppers are spaced one foot apart or one plant per square foot. Large plants like lettuce, chard and marigolds are planted 6 inches apart or four per square foot. Medium plants like bush beans, spinach and beets are spaced four inches apart or nine plants per square foot. Small plants like carrots, radishes and onions are space 3 inches apart or 16 plants per square foot. I think this might be too simple.
To see an example of the potential that dense planting has, search on your computer for a YouTube video on Noal's Farm radishes.
Other factors must be part of determining plant spacing: 1. Mature plant size, different varieties may need different spacing; 2. Disease, prone plants may require more spacing so they can dry off more quickly; 3. In-ground gardens, shadier situations, and needs of differently able gardeners may dictate different choices.
Last year I planted and had success growing carrots and green/bunching onions at 25 and 49 plants per square foot in my raised bed garden. These were on grids of 5x5 and 7x7 on a square foot. The spacings were 2.4 and 1.7 inches per plant which can be rounded to 2 ½ and 1 ¾ inch.
For about $25 you can buy a seed template online to help you space your seeds according to "Square Foot Gardening." You can make your own template or you can plant by eyeballing it, which also works fairly well on the less dense planting rates. I made my own seed template which overlaid the 25 and 49 seeds per square foot spacing. I can find on this square the other densities as well.
Square foot gardening can be practiced in the traditional soil garden also. I found it easier to calendar space my lettuce so it wasn’t all ripe at the same time. Harvesting the early maturing plants will give more room for the remaining plants.
Gardening is a learning process; what works well in one situation may not in another. Trying different gardening methods is part of that. University recommendations have been tested but not in “our” garden.
These local garden articles will reach you each week throughout the gardening season, but gardening information can be found year-round by clicking on "Yard and Garden” at the University of Minnesota Extension website, www.extension.umn.edu, or by visiting our Facebook page at www.facebook.com/Beltramicountymastergardeners.
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