The impact of wood ash on germination in onion seeds


Hello! I live in Toronto and want to know whether adding wood ash to soil will speed the germination time of onion seeds (i.e. the time it takes for a seed to sprout). I want to do this indoors. If onion seeds will not benefit from wood ash, are there any other plant seeds that a) do benefit, and b) germinate quickly (less than 14 days)? Thanks!


Dear Gardener,

Thank you for your interesting question regarding indoor onion seed germination. Your query re adding wood ash to the growing medium is reasonable, as ash contains potassium, or potash. But to be clear, each and every plant seed type has its own specific germination period, which can generally be nudged along by raising the temperature of the planting medium. Depending on the onion seed variety you choose, and the germination period indicated, once seeds have germinated, and roots established, then potassium can assist with strong root growth during the season.

Wood ash will add potassium to the soil, to make it less acid. It would be important not to let the ashes clump, to avoid nutrient salt damage, or ‘burn’, to the roots of your plants. One option of introducing potassium  is to incorporate finely sieved ash into your garden compost. Another option would be to store your dry ash, and make a “tea”, as required, by adding water to use for fertilizing during the growing season. You don’t mention the volume of seed you plan on starting — whether you want to grow a large volume in a greenhouse, or in a few trays in your home.

Your second question: there are some plants that will not benefit from potash — those that prefer acid soil, such as berry crops, grape vines and fruit trees. But tomatoes, cucumbers, carrots and many other root vegetables  benefit from potassium fertilizers.

One of the most informative research sites utilized by Toronto, and Ontario, gardeners is the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), and they offer HERE advice re growing members of the ‘allium’ species, including onions, leeks, garlic and shallots.

Dec. 31, 2021