Photo by Rachael Brugger
Those plants that work so hard to feed you—tomatoes, peppers, corn, potatoes, strawberries—well, they need to eat, too! Most edibles need lots of sunshine, plus a fairly rich and balanced diet of minerals. Macronutrients, including nitrogen, phosphorus, potassium, calcium, magnesium and sulfur, are important to most crops, as well as other micronutrients available in very small quantities.
Ideally, your edibles would be able to get their mineral diet from good-quality, compost-rich soil without any additional work or expense to you. However, only rarely are we gardeners blessed with perfect soil, and occasionally our plants need a little boost of concentrated nutrition. Sometimes your garden soil isn’t yet mature enough to support heavy-feeding crops; sometimes you grow demanding crops back-to-back, which is quite common in a home garden; and sometimes specific crops just need a little more of certain minerals. Root crops, for example, tend to perform better when given a bit more phosphorus. That’s when added fertilizers come in to play.
Choosing a Fertilizer
A fertilizer is anything that provides fertility to your crop. Fertilizers can be slow- or fast-release, synthetically or organically derived, and single-mineral or blended. Good old-fashioned compost is considered a slow-release, organic fertilizer because it contains small amounts of the minerals plants need, though I consider it more of a soil conditioner.
There are two basic ways to fertilize your crop: amending the soil and foliar feeding. We’ll look at both to show you how they work and help you decide the best method for your farm.
Fertilizer Method 1: Amend the Soil
To amend your garden soil, dig an appropriate amount of dry fertilizer into the garden bed before a crop is seeded or transplanted. As the plant grows, the roots of the plant have access to the fertilizer mixed into the soil, and chemically break off the mineral components needed by the plant.
After the crop is established, you can add fertilizer to the soil by side-dressing, aka banding. Lightly sprinkle your fertilizer of choice in the soil alongside plants, then gently work it into the top inch or so of soil. Side-dressing is typically done with granular fertilizer, but it may be done with liquid drenches for faster root uptake.
Feeding the soil is the most efficient way to get great results in the garden. When compost and other soil conditioners aren’t enough, adding soil fertilizers can help ensure your plants are getting the nutrition they need.
Making Amendments Work
Unfortunately, there is no one-size-fits-all fertilizer. Plants tend to grow to the level of least fertility. If one mineral is deficient, strong, vigorous plant growth isn’t possible. However, some minerals compete with each other or build up in the soil, so thoughtlessly adding fertilizers can do more harm than good. Adding an amendment your plants don’t need wastes money and can lead to compounded nutrient problems, excess salt in the soil and groundwater pollution. Therefore, your goal when using soil-amendment fertilizers is to balance fertility levels for optimum plant growth by supplementing minerals that are lacking.
If you aren’t sure what your soil needs, have a soil sample tested by a university extension or lab. Skip the at-home DIY test with the little colored pills—you’ll make up the moderate cost of a highly accurate soil lab test with better-targeted fertilizer purchases. The soil test will also tell you if your soil has a pH problem that needs correcting—a common reason plants are unable to thrive even if there’s plenty of soil nutrition available.
Is it For You?
Soil amendments work with the natural uptake processes of the root system and tend to support greater nutrient mobility throughout the plant. One of the biggest benefits, especially to farmers strapped for time, is that you can add a variety and quantity of fertility amendments at once. Plus, soil amendments are the only way to deliver long-lasting fertilizer to the root zone, and they’re typically less expensive than foliar applications.
However, there are things you need to watch out for when using soil amendments. Synthetic chemical fertilizers can easily be over-used in a landscape or garden. Even if direct harm to the crop is avoided, excess nutrients wash into the groundwater and cause pollution. Soil fertilizers, particularly organic fertilizers, are slower-acting than foliar feeds, so you’ll need some patience and planning. You also will need to have cash: Slow-release, coated synthetic fertilizers tend to be expensive.
I garden organically, and generally stick to the slower-release, organically derived fertilizers. In addition to regularly supplying my soil with compost and lime, I supplement with seed meal, used coffee grounds, gypsum, bone meal, fish meal and blood meal.
- A balanced organic fertilizer (2-2-2 or 5-5-5) from one of the major manufacturers is good for basic background fertility. Fish meal also supplies a nice balance of nutrients, with an emphasis on nitrogen.
- Gypsum supplies calcium.
- Bloodmeal is a fast-acting nitrogen source.
- Bonemeal supplies phosphorus.
- Seed meals typically supply nitrogen, plus lower amounts of phosphorus and potassium.
Fertilizer Method 2: Foliar Feed
Foliar feeding is the fertilizer method in which you directly apply a diluted liquid fertilizer to the leaves of the plant. The plant absorbs the nutrients in the fertilizer spray directly through the leaves. If amending the soil is like making sure your plants have enough food to eat, then foliar feeding is like giving your plants a shot of liquid vitamins.
Plants primarily absorb nutrients through their roots, and the amount and types of nutrients that can be absorbed via the leaves is quite limited. However, acute nutrient deficiencies can often be identified and corrected more rapidly via foliar fertilization than slower-uptake soil amendments.
Making Foliar Feeds Work
Healthy plant leaves have a waxy coating called the cuticle. This allows water to bead up and run off the leaf, dripping down and naturally irrigating the drip line of the plant. Foliar sprays must have a wetting agent added that allows them to penetrate that waxy coating. Commercial spray fertilizers will typically include a wetting agent, but DIY types can add a few drops of biodegradable liquid dish detergent to each gallon of dilute foliar fertilizer.
True foliar feeding, with fertility delivered solely through the leaves, is quite unusual in a backyard setting. Typically, when liquid feeds are used in a garden setting, plants are sprayed heavily. The vast majority of the liquid feed drips down to the soil, where it penetrates the soil and can be taken up by the roots. In this way, it becomes more like a liquid side-dressing or soil drench feed to the roots than a true foliar feed.
Is It For You?
Foliar feeds are ideal to correct specific nutrient deficiencies very quickly. Calcium, iron, potassium and zinc deficiencies respond particularly well to foliar feeds. In combination with soil drenching, foliar feeding can provide balanced background fertility, and if you also perform a leaf analysis, it’s a safe way to investigate nutrient deficiencies in specific crops.
However, it’s important to note that foliar feeds are often not the most efficient fertilizing solution. Major nutrients cannot directly enter the leaves of the plant in enough quantity to provide for the total requirement of the plant, and some nutrients aren’t mobile enough to migrate away from the leaves throughout the rest of the plant. Foliar feeds must be reapplied frequently unless underlying soil deficiencies are corrected, and the spray solutions risk burning delicate leaf tissue unless fertilizer concentrations are carefully measured. Not all nutrients and nutrient blends are well suited to foliar feed delivery, and typically products designed for foliar application are more expensive than equivalent soil-feed fertilizers.
Go-to Foliar Feeds
All foliar feeds work best when delivered in a very fine mist. A wetting agent is essential to help the feed stick to the leaves long enough to be absorbed.
- My favorite all-purpose foliar feed and soil drench is organic fish emulsion.
- Kelp based foliar feeds are popular because they are a rich source of micronutrients.
- Chelated iron is frequently used as a foliar spray used when native soil pH is too high to allow adequate plant uptake of iron. However, correction of soil pH is a better long-term solution.
Whether you use one of these fertilizing methods or a combination of the two depends on your farm’s soil, the crops you’re growing and your farming strategy. With some extra care and attention to what you’re feeding the soil, you have a chance at a healthy, productive crop for the upcoming growing season.