Everyone wants to grow big leeks. I get hits on my blog all the time from people searching the web for how to grow big leeks. Choosing the right variety, appropriate timing, a favorable climate and consistent water all help, but no leek will grow large without fairly heavy fertilizing over a long season. Manures work great, as do many other fertilizing stuffs, but just about the easiest and most effective fertilizer for leeks leaks out of your body every day... that's right, pee. This short post is an excuse to talk about using urine as a fertilizer, while focusing some traffic off the web for the commonly searched topics of growing large leeks and the occasional search for using urine to grow leeks and onions. Much of this has been said already in some form in other posts, but I have a lot of new readers and it never hurts to reiterate things that are awesome. I will be expanding on using urine as a fertilizer soon, with an emphasis on calming fears and busting myths.
There is increasing talk about soil mineral depletion and closing nutrient loops by returning human waste to the land instead of flushing it all away. We are essentially mining our soils of minerals and dumping them into the water, or putting them where they will do little good. Bad Human! You might be surprised to learn that the vast majority of nutrients useful to plants leave your body dissolved in urine. Most people are still hung up on trying to figure out composting toilets, which is a great idea and worth pursuing, but if we just divert our urine in the meantime, most of the problem of cycling the nutrients we consume is easily solved. Not only that, but compared to using human feces as a fertilizer, urine is much, much safer. Most recommendations are to apply it fresh with no treatment. I don't accept that it is 100% safe, but the fact is that I used it for years, and lets just say that I didn’t lose any sleep over the health risks.
The only reason I don't still use urine in my gardens is that I sell some of my produce at markets, and I don't think the bureaucracies that be, nor all customers would be stoked about that, besides which I can't be sure enough of the safety outside my family to expose quantities of other people without their knowledge. I’ll be looking at ways to “launder” urine before the nutrients make it back into the garden, like maybe applying to pasture and composting the resulting growth, or feeding the hay to stock to make manure.
You can do your own research on the subject and decide for yourself how safe it is. Ecosan, a group dedicated to making the shift from a waste paradigm to a resource paradigm regarding the stuff that leaves our bodies, is the best resource I've found out there and has a fair amount literature available. I use it either fresh or stale, it doesn't matter that much as far as the plant is concerned, though it may if you want to be picky about health concerns, but that will have to wait for another post. I don't eat very many leeks during the summer. They are mostly a winter and spring food supply. So, I tend to fertilize infrequently the further into winter we are, and not at all toward spring when the seem to do fine with the stores of nutrients available in the soil. Not that it matters a lot, since I always cook them and only apply fertilizer to the soil surface... not that I wouldn't eat them raw, just sayin'.
All three of the major plant nutrients N (nitrogen) P (phosphorus) and K (potassium) are well represented in urine with the balance leaning toward nitrogen. That's good, because the whole onion family, and especially leeks, are heavy nitrogen feeders. Also represented are an abundance of minerals, and all of it in a soluble form ready for plants to use. Finding out that pee is an awesome fertilizer was like the best gardening discovery ever! Suddenly I was completely free from worrying about scrounging for nitrogen sources, and most other fertilizers.
Since urine is soluble, it is somewhat more transient in the soil than some other more solid fertilizers. It doesn’t just flush right out of the soil though, as you might guess if you were to do some reading on soluble fertilizers. If your soil is alive with a decent organic matter content, all kinds of little guys in the dirt are going to snatch up those resources and start cycling them. If you way over water, it is possible to flush nutrients below the root zone, but it's not likely under most conditions. It still does need to be applied at intervals as the plants grow though. Growing large leeks takes a long season and using a soluble fertilizer is a great way to continue to pump those suckers up even if you’ve already added a bunch of stuff to the soil at the beginning of the season.
I don’t actually mix anything into my soil under normal circumstances. I throw some compost on top after planting as a sort of thin mulch, and also sometimes manure, seaweed and coffee grounds or whatever is around, but normally I rely on urine for most of the feeding ( or I did, now that is replaced by chicken manure tea which I have to say is much less convenient). If you could apply pee very diluted frequently, that would probably be pretty ideal, but I apply it at variable intervals when it’s convenient. Again, in a living soil, those nutrients will be cycled for a while. There is no need to over-think the thing or be on a obsessive schedule.
Leeks and onions can take a lot of nitrogen. I use a dilution that is between one third to one fifth pee, the balance being water, for general garden use. You can gauge by the health and growth of the leeks how much to use. Using urine on leeks is pretty fool proof, but it is a very strong fertilizer, and as such it is of course possible to over apply it. A watering can full of this mix can be put on a bed about 4 x 15 every few weeks, with some longer intervals here and there. You will have to get a feel for it over time. I’m not sure I’ve ever burned an onion or leek plant using too much fertilizer, and rarely see burning in other plants at this dilution, as long as it’s not applied too frequently, or in too great a quantity.
It is good to water in immediately. After all, if it’s not in the root zone, then the plants can’t use it. Apply enough water to flush the nutrients into the soil a distance. I’ll typically water for a while to get the soil wet, apply the fertilizer and then water a little more to flush it down into the soil and dilute it further. Early in the season, I dump it all over the plants, but as they get above about pinkie thickness, I start applying to the soil surface only, in order to prevent getting the stuff in the leaf bases where it’s hard to clean out. It helps a lot to have a well balanced long necked watering can like those made by Haws.