Mulch Ado about Onions (and Potatoes)

Published Feb 3, 2000

It always pays to repeat the trial! In 1998 it looked so clear. Angela and John Tedesco, Johnston, looked at the effect of mulching the onions that go to feed members of Angela’s Turtle Farm CSA. The experiment also examined the value of planting single onions or multiples in cell-packs of four at a time. In 1998 both mulching and multiple planting were winners – but that was then.

This was a new year and also a new site. Angela is buying some gently sloping land on Highway 17 at Granger. She also got her onions off to a better start before planting them out in 1999. And then there was the spring and early summer weather, which you couldn’t exactly call dry. So how about mulch in 1999? As Table 1, click to view, shows, the top yield of onions came from the unmulched plots where single onions had been planted! Overall, single-vs.multiple planting was not a statistically significant factor in yields, but mulching definitely was (Table 2, click to view).

Mulching also had a negative effect on transplant survival, and it significantly increased the total labor in 1999. In 1998 the weeds were bad enough that mulching saved as much weeding time as it took to distribute the mulch. In 1999, the stronger transplants competed better with the weeds – and maybe there are fewer weeds at the new site. Mulching saved precious moisture in 1998, but there was plenty of moisture during most of 1999. So the word on mulching may be: know when to use it. On the other hand, planting multiple onions instead of singles did reduce the total labor hours in both years. And in the more stressful conditions of 1998, multiple planting also benefitted yields.

Some on-farm research just doesn’t work out, and that was never clearer than in the mulching experiment attempted by Virginia and Marion Moser, Garrison. Virginia tried mulching potatoes with coffee bean hulls, a local resource she can get from Frontier Herbs. Here is a portion of her report.

June 5th – Applied mulch. It blew away in the night.

June 6th – Tried application again and it was too windy.

June 19th – I applied it again and it blew away. At this point we were soon going to be digging the first potatoes to sell, so I didn’t try it again. I learned that the coffee bean hulls can’t be used for mulch. They are like working with chicken feathers… I’m not going to give up on the coffee bean hulls, partly because they are free, but mostly because of the 2% nitrogen. I would like to use them in compost.