Speedwell is a winter annual weed. It will end its life cycle and die naturally once we have consistently warm temperatures. Photo: G. Rinehart
The warmer-than-normal weather during February had many people thinking about an early start to lawn and garden season. However, as temperatures have dropped and been below normal for much of March, it looks like we may have a couple more weeks before lawns really start growing. Lawn growth and crabgrass emergence are related to soil temperature, which is slower to change than the air temperature. While I have heard reports of soil temperatures topping out in the mid-50s for a day or two, it’s important to remember that in order to germinate crabgrass needs soil temperatures around 53-55⁰ F sustained for 5 days. These two things lead to a few questions, particularly pertinent this year when February felt like March and now March feels like late February.
Should I fertilize my lawn now?
While the legal window for applying fertilizer to lawns in Maryland began on March 1, that doesn’t necessarily mean you should fertilize your lawn just yet. Unless the grass is actively growing (which is dependent on warmer soil temperatures) it likely won’t take up and use the fertilizer—so you are better off waiting until the lawn is actively growing. Temperatures consistently around 60 and enough growth to warrant a second mowing are pretty good indicators of this. Keep in mind that if you fertilized your lawn in the fall you can probably wait until after the “flush of growth” in the spring (usually April/early May) and then schedule your spring fertilizer application for after that “flush” and leading into summer—usually around mid-late May. If you didn’t fertilize last fall it is tempting to try to “jump-start” the lawn in early spring with a fertilizer application, but hold off until the soil temperatures are consistently warmer and highs are around 58-60⁰ F on a regular basis.
Should I apply crabgrass pre-emergent now?
I would wait until soil temperatures are 53-55⁰ F sustained for 5 days. Keep in mind that your best defense against crabgrass is a dense turf that crowds out crabgrass seedlings. So, if you have good turf density and mow at 3” or higher, your overall crabgrass pressure should be lower anyway. The typical recommendation is to wait until the forsythia is “half green-half gold” (or even a little earlier), but with the warm February we had, that indicator may or may not be as accurate this year. You can check soil temperatures for your location at the following website: https://www.greencastonline.com/tools/soil-temperature.
Is there harm in applying crabgrass pre-emergent too early?
Probably not, unless it’s applied several weeks early and the product starts to break down before crabgrass even starts germinating. If you want to maximize the period of time your crabgrass application is effective, wait until when conditions are conducive to crabgrass germination and then apply it.
Roughstalk bluegrass (Poa trivialis) is a cool-season weed that shows up in early spring. If you only have a few patches, you can dig them out by hand (including the roots) and overseed to fill in the bare spots. Photo: G. Rinehart
On another note, this is now the time of year when many winter weeds become more noticeable as they are likely producing flowers and setting seeds. While you can apply selective products to control these weeds, remember that these winter annuals like chickweed, purple deadnettle, speedwell, henbit, etc. are almost at the end of their lives and will die naturally once we have consistently warm temperatures. Another weed often noticed this time of year is the grassy weed called roughstalk bluegrass (Poa trivialis). Seeds of this grass are often a contaminant in turfgrass seed mixes (the cheaper the seed, the more likely you will have weed seeds) and this grass starts growing much earlier than tall fescue. As the temperatures warm, it is not as aggressive and noticeable. There are few selective control products that are labeled for roughstalk bluegrass and they tend to be restricted to professional sites and/or are expensive. If you only have a few patches in your lawn, digging these out (including the roots) and then re-seeding the spot with a soil-tall fescue mix is the best control approach for most homeowners.
As a newer gardener, I have not previously gotten around to using soil test information. I’ve been planning an ornamental overhaul in a small area of my yard and wanted to soil test to make sure the plants added to the area had the best chance of success. The HGIC website has a lot of soil test information, but I’ve never looked at it closely myself until now. Even though our content is well-written and organized, the subject is intimidating with many choices to make, multiple steps, math homework to figure out how much fertilizer to use in your space, and as I learned, many caveats or roadblocks. I can see plenty of people just giving up and not adding any soil amendments, or just going to the hardware store and buying a bag of fertilizer and applying without thinking too much about it.
Even after reading our material thoroughly, I still needed several questions answered from our experts. I’ve got a handle on it now, for the most part. With this post, I hope to detail how I figured out what fertilizers I needed, how to apply it, and then the most important things I learned that I didn’t feel are made clear.
The goal
I’ve got this space in my backyard that wasn’t being used for much. In the summer of 2020, mid-pandemic, pre-offspring, I decided to revisit a teenage hobby of mine – remote control cars. I took a shovel and cleared out an area and built ramps and hills out of dirt, for my very-own mini-dirt track. 2 years later, my wife asks me “are you going to keep the track? It’s ugly.” So, my task is to beautify it with improved landscaping and added vegetation. We also have a bunch of hostas in our front yard garden that keep getting eaten by deer. Our backyard is smaller and enclosed, so we hope the hostas will avoid attack in their new backyard, trackside location. We are also adding other plants good for shade conditions.
March, before landscaping beganJune, landscaping work pretty much completeJuneJune – landscaping complete. New plants, mulch, grass growing in infield, and this year, I’m allowing the moss to keep growing on the straight.
The location is on a bit of an incline, with the higher elevation area being more sandy and rocky, and the bottom softer and wetter. There is an “infield” of the track that is often stood on that is grass, but has been overtaken with weeds. I am planting nice plants and shrubs around the outside, and re-seeding the infield with grass. Since I know from a lot of digging to make the track that the soil is quite different in different areas, I wanted to soil test so that I could find out what exactly I might need to do to make sure the plants have the soil they need in their different locations.
You’re getting ready to plant vegetable seeds and transplants for the first time and trying to make sense of the conflicting advice you’ve been getting from HGIC, a neighbor, and your brother-in-law. You want to grow your vegetables organically but now realize that you don’t have a clue about fertilizing. Are there enough nutrients in the not-so-great soil or in the “potting media” used to fill a raised bed? What type of fertilizer should you use? How much and when? Take a deep breath and relax. You and your plants are going to get through this together.
Step 1: Test your soil
Your plants will get most of the nutrients they need from air and water, and the minerals and organic matter in the soil. Soils vary quite a bit, and soil testing is the surest way to get important baseline data on soil pH (affects nutrient availability), nutrient levels, organic matter content, and the amount of lead (Pb) present. After carbon, oxygen, and hydrogen, the nutrients needed in the greatest amounts are nitrogen, phosphorus, potassium (the primary macro-nutrients), and calcium, magnesium, and sulfur (the secondary macro-nutrients). Basic soil tests also include some micro-nutrients required in very small quantities, such as molybdenum, copper, zinc, and boron.
The lab sends you a report showing which nutrients are in the medium-excessive range (no worries) and which are deficient (you’ll get fertilizer recommendations). Labs don’t test for nitrogen because it changes quickly, moving between organic forms (immobilized inside living organisms) and inorganic forms (mineralized as ammonium and nitrate).
It’s ok to start gardening if you missed Step 1, but try to test your soil sometime between now and the fall.
Step 2: Feed the soil to feed your plants
Soil organic matter is made up of living and dead organisms- plants, bacteria, fungi, earthworms, and countless others. Nutrients, like the nitrogen needed to build proteins, are locked up in organic compounds in living organisms. When plants and animals decompose, these nutrients are transformed into inorganic forms, available for use by plants and soil microbes.
So, soils really do feed plants. Adding organic matter in the form of plant residues, compost, organic mulches, and cover crops will increase soil organic matter levels and ensure a slow and steady supply of plant-available nutrients. Organic matter also improves the structure of the soil, allowing for better movement of air and water, and a better home for plant roots and soil critters.
Vegetable crops, as a group, are “heavy feeders” compared to annual flowers and perennials and compete poorly against scrappy weed species for soil nutrients. They need our help to ensure strong, continuous growth. After carbon, oxygen, and hydrogen, nitrogen is the nutrient required by plants in the greatest amount. For each 1% of soil organic matter, about 0.4 lbs. of nitrogen/1,000 sq. ft. is available for plants (conservative estimate). A soil with a 5% level would release about 2 lbs. of nitrogen/1,000 sq. ft. which is a typical nitrogen recommendation for vegetable gardens. The problem is that organic matter may not be able to supply sufficient nutrients at particular times of the season and at particular stages of plant development. Nevertheless, many people with well-established, high organic matter gardens, forego supplemental fertilizers and get large harvests.
Compost is mixed with soil before planting chile pepper. The compost will supply a portion of the nutrients needed for high yields.
Step 3: Types of organic fertilizers
Fertilizers are regulated materials that contains at least one plant nutrient. The nutrient content is guaranteed by the three numbers (e.g., 3-4-3) found on a fertilizer bag or container. Also known as the nutrient analysis, the numbers represent the percentage, by weight, of nitrogen (N), phosphate (P205), and potash (K2O), respectively.
A complete fertilizer contains all three of the primary macro-nutrients. Some fertilizers contain only one or two of the three major nutrients, such as nitrate of soda (16-0-0), a good choice when your soil test indicates high levels of P and K.
Commercial organic fertilizers are relatively low and variable in nutrient content, and typically release nutrients more slowly than synthetic fertilizers. They are also more expensive to buy on a per pound of nutrient basis. Many are made from composted or processed animal and plant waste products, such as fish fertilizers, composted manure, and cottonseed meal. A number of products are blends of several organic ingredients. Some organic fertilizers are inorganic materials (lack a carbon backbone), such as rock phosphate, and sodium nitrate.
Vegetarian or vegan fertilizers are all plant-based, like alfalfa meal and yard waste compost. Some organic fertilizers sold to home gardeners carry OMRI (Organic Materials Review Institute) certification. Farmers participating in the USDA’s National Organic Program can only use OMRI-certified fertilizers. Gardeners are not restricted in this way.
Some Organic fertilizersNutrient analysisNutrient release rate
Fish emulsion 5-1-1 fast
Bloodmeal 15-1-0 med-fast
Cottonseed meal 6-2-1 med
Alfalfa meal 3-1-2 med
Nitrate of soda 16-0-0 med-fast
Dried poultry litter 4-3-3 med-fast
Mushroom compost 2.5-1.5-1.5 slow
Rock phosphate 0-14-0 very slow
Muriate of potash 0-0-60 med-fast
Nitrate of soda is a mined mineral. Organic farmers can use this particular, single nutrient fertilizer because it’s OMRI-certified.
This is a complete liquid organic fertilizer that is not OMRI-certified but is safe and effective for organic gardeners.
Step 4: Let’s fertilize!
How much?
Use test results, crop conditions, and product instructions to guide your decisions on how much fertilizer to apply. For example, a new garden with only a moderate amount of organic matter and without the benefit of a soil test report, should be fertilized according to the label directions. You could reduce the amount somewhat if you added a large amount (>2 inches) of compost.
When factoring in nitrogen contributions from compost take into account that only 5-10% of the N is available the first year following application.
In a relatively small garden with just a few plants of several vegetables it is fine to fertilize all crops the same.
Sweet potato, Southern peas, cucumber, okra, squash, and beans need less nitrogen than crops like tomato, pepper, eggplant, broccoli, leafy greens, lettuce, spinach, and sweet corn.
Raised beds and containers, filled with soilless growing media and/or compost, need to be fertilized more regularly depending on the crop and growing conditions.
Experiment with reducing fertilizer amounts and the number of applications once you reach a 5% soil organic matter level.
Think before fertilizing
Excess nitrogen can reduce flowering and fruiting and cause plants to be overly succulent and more vulnerable to sucking insect pests.
Organic gardeners contribute to water pollution when they use excessive amounts of fertilizer and don’t prevent stormwater run-off and soil erosion.
The nutrients in synthetic and organic fertilizers come in the form of salts. If a large amount of any fertilizer remains in direct contact with plant roots, leaves, or stems, you may see some injury symptoms. This “burning” is known as phytotoxicity.
Fertilizer can’t bring a sick plant back to health if the problem is not a nutrient deficiency. Symptoms such as slow growth and low productivity could be caused by many factors including, lack of light, poor soil conditions, limited root system, and weather extremes.
When?
For long-season crops that produce fruits (tomato, pepper) or heads (cabbage, broccoli) you can apply half of the recommended amount of fertilizer right before planting and the other half when fruits start to form.
Early season crops benefit from complete, quick-acting liquid fertilizers, or compost tea. “Starter fertilizers” high in phosphorus (P) are not beneficial because most plants need 4X more nitrogen than phosphorus.
Perennial crops, like asparagus and rhubarb, are fertilized in early spring and after harvest.
Where and how?
Sprinkle dry fertilizer evenly over the area where plants will be growing and not in walkways. Mix it into the top 4 inches of soil.
For vegetables that are spaced far apart, like eggplant, tomato, and squash, mix the fertilizer into the planting hole soil or the area where seeds are planted.
Water the area after fertilizing, especially when fertilizing during hot, dry weather.
“Side-dressing” is applying fertilizer around or alongside established plants (pull back organic mulches first). If possible, gently incorporate the fertilizer into the top 1-2 inches of soil.
Step 5: Fertilizer recommendations from soil test reports
Labs will often recommend urea (46-0-0) as a nitrogen source when phosphorus and potassium levels are high. You can select an organic fertilizer that only contains N (nitrate of soda) or one with an N content much higher than the P and K content (bloodmeal, cottonseed meal).
This U. of DEL soil test report recommend only nitrogen for a vegetable garden that tested “excessive” for other macro-nutrients. Note the very high % of soil organic matter. Labs do not credit the expected nitrogen release from soil organic matter when making fertilizer recommendations.
The soil test report above recommends 1 lbs. of N/1,000 sq. ft. which equals about 2.5 lbs. of urea.
If you decide to use bloodmeal you will need 7.6 lbs. (46% divided by 15% X 2.5).
Cottonseed meal, soybean meal, and alfalfa meal are dry, organic fertilizers with a relatively high N content.
Use simple algebra to convert a synthetic fertilizer recommendation to an organic recommendation.
Example: the recommendation is to apply 20 lbs. of 10-10-10/1,000 sq. ft. and you wish to substitute cottonseed meal (6-2-1).
Divide the percentage of N in the synthetic fertilizer by the percentage of N in the organic fertilizer and multiply by 20:
0.10/0.06 (or 10%/6%) X 20 = 33.3 lbs. of cottonseed meal
Without the benefit of a soil test how do you fertilize a 100 sq. ft. garden with cottonseed meal, a complete organic fertilizer (6-2-1)?
Calculate the amount of the fertilizer product needed by dividing the pounds of N needed by the percentage of N in the product.
Let’s assume we need 2 lbs. of nitrogen per 1,000 sq. ft. or 0.2 lbs. of nitrogen per 100 sq. ft.
0.2 (lbs. of N) divided by 0.06 (% of N in cottonseed meal) = 3.33 lbs./100 sq. ft.
Having a soil very low in P can be a challenge for a strict organic gardener. Rock phosphate (the primary organic P source) has a low P content and is very slow to break down. Superphosphate (0-20-0) and triple superphosphate (0-46-0) fertilizers are made by treating rock phosphate with sulfuric acid and are much faster-acting. These products are available for gardeners but are not allowed for use by organic farmers.
Step 6: Observe, engage, enjoy!
Take notes on your garden this year and record your successes, failures, and ideas.
Q: I didn’t get around to fertilizing my lawn earlier this fall. Is it too late to put down fertilizer now? Should I wait until spring?
A: November 15 is the cutoff date for Maryland homeowners to fertilize their lawns in the fall. According to Maryland’s Fertilizer Use Act that went into effect in 2013, you may not apply lawn fertilizer between November 15 and March 1. The law also prohibits lawn fertilizer applications within 10 to 15 feet of waterways. These restrictions are intended to help protect the Chesapeake Bay from excess nutrient runoff.
