Troubleshooting Garden Soil: 3 Common Soil Problems and What to Do About Them
Good soil is the foundation of a healthy, high-yielding vegetable garden. If your plants just don’t seem to grow well or produce much no matter how much careful planning and tending you do, it’s likely the problem isn’t your routine (or the color of your thumb!) It’s time to look deeper and investigate what’s going on with your soil.
Understandably, new gardeners usually just add some fertilizer when their plants aren’t looking good. But there’s a decent chance the root cause is more than just a lack of nutrients in the soil. A few common underlying soil issues can stress your plants out, invite disease, and prevent them from absorbing essential nutrients (even if those nutrients are available).
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1. Soil Imbalances and Nutrient Deficiencies
Plants that don’t have access to enough nutrients in the soil grow poorly and fail to thrive. Without a well-supported immune system, deficient plants will turn yellow, drop leaves, and fall victim to disease. They’re also more likely to become infested with little nuisance pests like aphids, whiteflies, or mites.
How to Spot Nutrient Deficiencies in Your Plants
Stunted growth and leaf discoloration are telltale signs your plants are missing something. But since symptoms can look different depending on the plant, it’s sometimes tricky to pinpoint exactly what’s lacking.
Deficiencies in the three macronutrients, nitrogen, phosphorous, and potassium, usually cause symptoms that appear in the lower leaves to start with and then move up the plant. Lack of magnesium, an important micronutrient, also affects the lower leaves first. Here are some more specific signs to look for:
–Nitrogen deficiency causes plants to turn pale and, in severe cases, stop growing almost altogether. Lower leaves turn yellow and eventually fall off.
–Phosphorous deficiency can cause lower leaves to turn purple, brown, yellow, or all three. You may also notice purple or brown spots on leaves and slowed growth.
–Potassium deficiency often causes leaf scorch or browning of leaf edges.
–Magnesium deficiency causes yellowing between the leaf veins.
Deficiencies in other micronutrients like manganese, iron, and sulfur affect the new growth, first. Newly emerging leaves might be pale or yellow, with yellowing sometimes between the veins or at the base of the leaf. Lack of calcium, another important mineral, leads to blossom end rot of fruits (particularly tomatoes), deformed or curled new leaves, and even dieback at the growing tips.
What Causes Nutrient Deficiencies?
If you’ve had trouble with nutrient deficiencies and stunted growth in your garden, the best way to find the culprit is to get a soil test done. A basic test will tell you the pH and how much of each essential nutrient is present in the soil. That’ll take much of the guesswork out of it, and you won’t have to deal with a lengthy and frustrating trial and error phase.
*Note: If anyone says you need a $100 mail-in soil test kit to get real answers about your soil, they’re trying to turn a profit. Most counties have a cooperative extension office that will test your soil for under $20. Ours currently charges $12 for one sample and $6 per each additional sample, if you want to test different areas of your garden at the same time.
PH Imbalances
Most annual vegetable plants can best take in nutrients when the soil pH is slightly acidic to neutral, or somewhere between 6.0 and 7.0. They’ll usually tolerate a pH somewhat outside of this range, but they’ll start to struggle if it’s below 5.5 (very acidic) or above 7.5 (very alkaline).
Very acidic soil makes the essential nutrients like nitrogen, phosphorous, potassium, and magnesium less available to your plants. Meanwhile, if the pH is too high, plants will have trouble accessing phosphorous and important minerals such as iron.
Your basic soil test will give you an accurate reading of your soil’s pH. If you haven’t done a soil test, you can buy soil pH test kits at garden centers. However, I’ve found those test kits to be off by quite a bit when comparing their results to the professional soil test results.
What Causes pH Imbalances?
Healthy, fertile soil is rich in organic matter, which has a balancing effect on soil pH. If you’ve started a garden where lawn grass used to be, especially if you live in a region that gets plenty of rain, there’s a good chance the soil’s pH is on the low side. Soil beneath a lawn tends to be low in organic matter compared to soil in nature.
Other factors can also contribute to or cause pH imbalances, such as hard water, over application of certain fertilizers or amendments, or natural minerals present in the soil. For example, some places have a lot of limestone around, which creates alkaline soil conditions.
How to Correct Soil pH Problems
In newer gardens, an off-balance soil pH, especially if it’s too acidic, is often just a sign the soil needs a little more amending. Add plenty of organic matter like compost and natural mulch (preferably in the fall!), and it’ll gradually bring the soil’s pH into the ideal range.
Composted organic matter, or humus, has a near-neutral pH. That means it’ll help balance both acidic and alkaline soils. It also improves your soil’s buffering capacity, or ability to withstand pH changes, and offsets the effects of pH on nutrient absorption. Even if your soil’s pH isn’t perfect, lots of organic matter will make essential nutrients more available.
If your soil’s pH is REALLY off, such as below 5.5 or well above 7.5, it’ll cause crippling effects in many veggie plants. Applying a pH-specific amendment can bring it to a reasonable level a little faster so you can have a successful harvest. You can use agricultural lime or wood ash to raise the pH of highly acidic soil. Elemental sulfur sometimes works for lowering pH when the soil is too alkaline.
Adjusting pH is a slow process, so you’ll need to amend at least several months before you plant. For more about soil pH problems, using pH adjustors, and planning crops that can grow well in your soil’s current pH conditions, read this post: Gardener’s Guide to Soil pH: Why it Matters and How to Correct pH Problems.
Nitrogen Lock
Newly planted seedlings are prone to transplant stress, especially in the spring. A bit of yellowing in the lower leaves and a pause in growth is pretty normal as the plants adjust to their new environment. However, if the plants don’t improve and start growing within a week or two, you could be dealing with nitrogen lock.
Nitrogen lock happens when the soil contains too much undecomposed carbon materials, like wood, bark, or shredded leaves. As they finish breaking down, carbon materials temporarily tie up or “lock” the nitrogen available in the soil, preventing your plants from taking it in.
This problem often shows up when folks fill raised beds with store-bought potting soil or other bagged soil products. Unfortunately, some garden supply companies are loading their soil products with fillers like raw wood chips to make their supply stretch. Tilling amendments like shredded leaves or bark chips into your garden soil can also lead to nitrogen lock problems, if they don’t have enough time to break down before you plant.
How to Handle Nitrogen Lock
Nitrogen lock is a temporary problem, since the locked nitrogen will become available again once the carbon finishes decomposing. In the meantime, the best remedy is to feed your struggling plants with a water-soluble fertilizer that’s high in nitrogen.
Water-soluble fertilizers are immediately available to the plants, without the need for soil biology to break them down first. If you want to stay organic, you can try liquid fish emulsion for a quick nitrogen boost.
While they do have their drawbacks, a conventional water-soluble fertilizer is another option for severe nitrogen SOS. Nitrogen levels are relatively low in organic fertilizers, so a product with synthesized nitrogen can offer suffering plants a stronger dose and a quicker fix. If you feed with a synthesized fertilizer, be sure to dilute the product so it doesn’t burn your plants. 1/4 to 1/2 the recommended amount is a good place to start for stressed and fragile seedlings.
To speed up the breakdown of woody bits in your raised bed soil, mix in a lot of good, finished compost. That’ll boost the population of beneficial fungi and microbes to help the process along.
Preventing Nitrogen Lock
To keep nitrogen lock from becoming a problem in raised beds or containers, avoid filling them with bagged potting soil or bagged “raised bed” soil from chain stores. Those products are the worst to be full of wood and bark. Instead, fill them with a DIY raised bed mix, such as a 1:1 blend of good-quality topsoil and compost.
Check with local nurseries and ask any neighbors who garden to find a good source of bulk soil and compost in your area. Bulk soil products from smaller businesses are often better quality (and better value). Some cheap bagged topsoil products will also work fine for your raised bed mix, but some are heavy on woody bits. Wherever you get your topsoil from, inspect it for excess wood or bark before adding it to your mix.
If you plan on tilling or mixing high-carbon organic amendments into your garden soil, get it done in the fall so they have plenty of time to break down.
Nutrient Toxicity
Sometimes, too much of a certain nutrient in the soil can block your plants’ ability to absorb other nutrients. For example, ultra-high levels of phosphorous can prevent your plants from absorbing important minerals like zinc, calcium, and iron. Too much magnesium can limit potassium intake.
Off-the-charts nutrient levels are almost always the result of over-fertilizing or fertilizing blindly. Even organic fertilizers can build up in the soil and cause problems over time, when used in excess. Heavy applications of cow manure are known for causing phosphorous buildup, while overdoing it with Epsom salt can lead to excess magnesium in the soil.
If you’re working with a new garden plot where you’ve never fertilized before, keep in mind that some native soils are naturally high in certain nutrients. Our native soil is already quite high in phosphorous, as is often the case with clay soils. That means we don’t need to fertilize for P in our in-ground beds. If we were to use a bunch of high-phosphorous fertilizers like bone meal and manure, it could throw things out of whack.
What to Do About Excessive Nutrients in the Soil
Toxic nutrient levels aren’t always easy to fix, especially when you’re dealing with nutrients that aren’t very soluble, such as phosphorous. This is why it’s important to get your soil tested at least once before loading your garden down with lots of amendments.
Working towards a healthy and active soil biome is the best approach to correcting a problematically high nutrient level. Add organic matter, keep the soil mulched and moist, and consider growing cover crops between your main crops to help absorb the excess nutrients.
If your only evidence of nutrient overload is a pre-planting soil test, don’t take drastic measures yet. Just wait to see how your plants do. Nutrient levels way above the ideal amount don’t always cause toxicity effects. It depends on a lot of factors, like soil pH, soil conditions, and how much of that nutrient is actually available. A high reading is, however, a good reason to pay attention to the fertilizers you use.
Low Nutrient Levels
Sometimes, the problem is as simple as low nutrient levels in the soil. Your soil might be depleted from growing heavy-feeding crops, or it might just be naturally low in certain nutrients. Soil that’s low in organic matter tends to be low in nitrogen, by default.
Once you get a soil test to confirm what your soil is deficient in, you can amend to raise those low nutrient levels. See this post to learn how to fertilize your garden naturally, plus some good fertilizer options you can use for all the essential nutrients:
Fertilizing Your Garden Organically: The Basics + Some Natural Fertilizer Options
*Note: Some basic soil tests don’t account for nitrogen, since nitrogen levels in the soil change a lot from season to season. For quick-growing annual vegetables, feeding young plants with a little high-nitrogen fertilizer like fish emulsion, feather meal, or blood meal is generally a good idea. Root vegetables are the exception; since nitrogen produces lots of top growth, go sparingly on it for those, or you’ll end up with small roots.
2. Poor Moisture Retention and Moisture Fluctuations
Most plants need even and consistent soil moisture to properly absorb nutrients. Wacky fluctuations in soil moisture can all cause symptoms of deficiency, even if those nutrients are present in your soil. You might also see curling leaves, flower drop, and poor fruit quality.
As an example, blossom end rot in tomatoes happens when the plants can’t get enough calcium. This deficiency is almost always due to water issues, since most soils contain calcium. Inconsistent soil moisture can cause other deficiencies to show up, also.
Sometimes, the underlying issue might just be the gardener’s watering routine. If you allow the soil to dry out too much or keep it constantly soggy, your plants’ roots will struggle to absorb nutrients properly. Ideally, you want to water deeply and wait until the soil surface is dry an inch or so down before watering again.
In a lot of cases, problems with moisture retention complicate the issue. If your soil dries out so quickly you end up needing to water almost every day, those constant swings in moisture will mess with your plants’ nutrient uptake. Watering too frequently can also wash out nutrients and deplete the soil.
When you’re growing in raised beds or an in-ground garden, you shouldn’t need to water more than once or twice a week, max. If you do, your soil isn’t holding onto moisture well enough.
How to Improve Moisture Retention
Putting down a nice layer of mulch will do a whole lot to prevent your soil from drying out too fast after watering or rain. Your mulch should be thick enough you can’t see bare spots of soil peeking through. If you live in a hot climate, using a lighter-colored mulch like straw or pine needles can help reflect heat and keep the soil cool and moist.
Pots, grow bags, and smaller planters tend to dry out a bit too fast even with mulch, when it’s hot out. To boost their moisture-holding ability, you can try adding something like coco coir or perlite to the planting mix.
Sandy or silty native soils that drain too quickly will also have trouble with moisture retention during hot weather. On top of mulching, regularly adding compost and organic matter helps improve the soil structure so water retention becomes less of a problem.
3. Poor Drainage and Compaction
Drainage problems and soil compaction are two problems that often have the same cause: clay-heavy soil that’s low in organic matter. Soil that was well-loosened and manageable in the spring turns into something more like concrete around your plants’ stems, after several weeks of summer thunderstorms and hot afternoons. When you get a lot of rain, it might puddle or stay muddy for days.
Lots of compaction can hinder your plants’ root development and overall growth, since the roots have trouble pushing through rock-hard soil. If your soil doesn’t drain quickly enough, standing water can smother the roots and prevent them from taking in enough nutrients. Worse, it can lead to root rot and rampant fungal disease during a rainy summer.
If your soil is compacted and/or holds water for too long, your plants’ growth may be stunted. They may have symptoms of overwatering, such as curled, drooping, or yellowed leaves.
How to Fix Compaction and Drainage Issues
To improve soil structure so your soil doesn’t compact or get waterlogged so easily, the main order of business is to amend with plenty of organic material like compost and aged manure (see a trend, here?).
Some more tips for dealing with compaction and drainage problems:
Use cover crops between your main crops. Cover crops with deep roots loosen and aerate the soil, and the leftover crop residue contributes a lot of organic material for improving soil structure.
Keep the soil well-mulched whenever it’s unoccupied, such as over the winter or the hottest part of summer. A good mulch layer protects the soil from the compacting effects of pounding rain, snow melt, and constant freeze and thaw cycles.
Don’t fill raised beds with potting mix. Potting mix is meant to hold moisture for as long as possible in small containers that dry out quickly. In a bigger space like a raised bed, it may hold onto that moisture for much too long, leading to waterlogged roots. That’s another good reason not to use bagged soil mixes in your raised beds.
If you’ve already got raised beds full of potting soil, you can improve their drainage capacity by mixing in good-quality compost, along with a little coarse sand, well-rotted leaf mould, or vermiculite.
Plant on berms or raised rows to keep root crowns out of soggy areas, in an in-ground garden. Even if your soil isn’t perfect, elevating your plants a bit above ground level will prevent a lot of issues. Use extra compost and/or some soil from your walkways to build the soil up higher where you’ll plant. Building hügelkultur mounds is also a great strategy if your garden spot has drainage issues.
Aerate or loosen your soil several times per year. For folks who till, this means going through with the tiller in the spring before planting and usually again in the fall after the last harvest. If you’re using no-till methods, you can make aeration holes throughout the garden with a broadfork or digging fork. In my experience, the broadfork is the easiest and most effective tool to use for aerating no-till garden beds.
And, speaking of no-till:
Consider switching to no-till gardening methods. While tilling does help with compaction, it’s a temporary fix that needs to be done regularly to maintain workable soil. It can also make heavy soils like clay more prone to compaction, over time.
No-till methods work by encouraging worms, microbes, and friendly fungi to thrive in your garden and improve soil tilth through natural processes. Living soil with a healthy microbiome is more resistant to compaction and drainage troubles, without the need to constantly turn and work it.
See this post to learn how no-till methods can improve heavy clay soil: Gardening in Heavy Clay: How a No-Till Strategy Can Transform Tough Soil.
Problems with soil quality often take time to correct, especially if you’re working with tough native soil that hasn’t been cultivated or amended much yet. So, don’t throw in the towel if your garden doesn’t produce as much as you’d hoped at first. Keep working at building healthy soil, and you’ll see more and more improvement each season.
