Hello, busy gardeners! I hope you’ve been enjoying our local abundance of plant sales and that your gardens are thriving. This month’s reader questions were about fertilizers and weeds, and my answers are practical and, hopefully, mind-expanding.
Before we jump into those, a reminder to email me your questions at firstname.lastname@example.org. I look forward to hearing from you!
How much nitrogen to add to garden soil?
Nitrogen is a very important part of soil fertility, as it fuels green growth in all plants. When vegetables are looking yellowish or not growing well, it’s likely due to a lack of nitrogen. However, too much can inhibit seed germination, as well as flowering and fruiting, while increasing susceptibility to pests, leading to large vegetables that lack in flavor. As with much of our lives, balance is key.
Too much of a good thing
Another important quality of nitrogen is that it’s extremely water soluble, meaning it is unstable and can easily leach out of soil. Loss of nitrogen is much greater in uncovered soils with low organic matter, so caring for overall soil health is a way to keep nitrogen levels optimal. Regular additions of nitrogen in some form are important, however, overapplication of nitrogen fertilizer can run into creeks, streams and groundwater. This runoff causes plants and algae to grow in waterways that choke out oxygen, knocking the whole system out of whack. Nitrogen pollution is a huge problem with profit-driven industrial agriculture that uses highly concentrated and volatile sources of this nutrient.
When it comes to the right amount of nitrogen, a good place to start is the application rate suggested for vegetables on the product that you’re using. There are lots of organic nitrogen sources out there, including feather meal, alfalfa meal, blood meal, cottonseed meal, poultry manure products, soybean meal, fish emulsion, etc. Interestingly, bone meal, which was brought up in the reader’s emailed question, is fairly low in nitrogen but high in phosphorus.
Compost and manure also contain some nitrogen, though in much lower amounts than the more concentrated products. The nitrogen in compost and well-rotted manure, however, is more stable and less likely to cause problems with leaching. Another good source of long-term, slow-release nitrogen is cover cropping, which, along with mulching, can help a lot with nitrogen retention as well as addition.
Ideally, you would mix in a moderate amount of nitrogen before planting (i.e., the suggested application rate, or a little less), then add more after plants are really off and growing, if need be. Liquid fertilizers are easier to add after the fact than powders, although both are doable. To add meals and powders to already established plants, simply sprinkle the fertilizer around the base of the plant (not touching the plant) and scratch it into the soil about half an inch with your hand or a small hand tool, then water it. For liquid fertilizers, just mix them at the appropriate rate with water in a watering can, or use a hose with a siphon mixer.
Use pee, it’s free!
My all-time favorite nitrogen fertilizer is pee. Yes, human urine! It’s rich in nitrogen and phosphorus, as well as lots of secondary and micronutrients that plants need for growth. Your pee is basically a well-balanced plant food that comes right out of your body every day, at no cost. I use it as a liquid fertilizer, mixed 50/50 with water. To learn more about fertilizing with pee and about soil fertility in general, check out the Wild Abundance Online Gardening School that I co-created, avl.mx/bbd.
What to do about dandelions?
Another reader asks if there is a nontoxic way to rid yards and gardens of dandelions, outside of rooting them out by shovel or hand.
The answer to this question is no and yes. Indeed, the most effective, nontoxic way to remove existing dandelions from your yard is to dig them up. And, I hate to say it, but completely ridding your lawn of this “weed” is not possible without repeated applications of harsh chemicals (which might not even completely solve the issue). The good news is that there are several strategies for minimizing the spread of dandelions that don’t involve pesticides, as well as great ways to enjoy the health benefits of dandelions.
First, let’s reframe how we think about dandelions in our landscapes. Common dandelion (Taxacum officinale) is considered native to Eurasia and was likely brought to this continent on purpose by some of the first colonizers/settlers on the Mayflower. Those invasive humans brought this invasive plant due to its nutritional and medicinal benefits: Dandelions aren’t just great for pollinators, they’re great for people, too! The tenacious herb spread across what we now call North America faster than the people did and became integrated into many Indigenous systems of food, medicine and culture as a source of nourishment and healing.
Eat the weeds
All parts of the dandelion plant are edible and medicinal. Dandelion roots contain prebiotic fiber that’s good for the gut and supports healthy liver function and blood flow. The leaves are nutrient rich and also support the digestive system, liver and blood. That bitter flavor and milky sap that help us identify dandelions are also both part of its glorious gifts. Instead of composting plants that you dig up, add the leaves to your salads or sautée them, and make a nourishing, cleansing tea from the roots (as long as they haven’t been sprayed with toxic chemicals). To learn more about the medicinal and culinary qualities of dandelion and other weeds and herbs, check out the Chestnut School of Herbal Medicine, based here in Asheville, avl.mx/blh.
Phosphorus, calcium and shade
One of the dandelion’s strengths is that it readily grows in poor, degraded, exposed soils. It’s like an ecological triage nurse, rushing in on the wind to bring life to landscapes in need of organic matter and coverage. Luckily, we can learn from the dandelion’s good will and leverage these qualities in our quest for grassier lawns. As benevolent pioneers, dandelion seeds need light to germinate. If your grass is dense and left on the thicker side (not mowed extremely low), the shade it casts can hinder dandelions from sprouting.
Furthermore, when you nourish your lawn with compost, manure or even just lawn clippings, you can build up organic matter in the soil over time. Unlike most garden veggies, and your lawn itself, dandelions actually don’t thrive in soils with high organic matter. They’re also averse to high phosphorus, so sprinkling an organic phosphorus source like bone meal can help dissuade them from taking over.
Another flavor that dandelions dislike is calcium. Most of our soils in this area are fairly low in calcium, making it especially inviting to dandelions. Sprinkling a calcium source like high-calcium lime can help deter these sunny opportunists, as well.
Finally, if you’re really on the defensive, an organic, nontoxic product called corn gluten meal is effective at inhibiting dandelion germination; it stops the seeds from sprouting. This affordable product can be found at most garden stores and is sprinkled directly onto the lawn. Don’t put it on your garden, as it will inhibit most vegetable seeds from sprouting, too!
Dig it out
As for full-grown plants, digging them up is really the most effective strategy. When you do this, keep in mind that dandelions will readily resprout from both the crown and roots. That means you need to get the entire plant out of the ground, otherwise it will grow back. The easiest way I’ve found to do this is with a small hand trowel or a larger digging fork. I spend time loosening the soil all around the dandelion before even tugging on it, lest I break off the aboveground parts. Once the soil is nice and loose, I grab the leaves as a handle and gently rock and pull until it comes out in one piece.