Identifying Nutrient Deficiencies in Your Garden (Part I)
Our gardens are complex, dynamic, interconnected and ever-changing. Which means there is always something new to learn. For someone just starting out in their garden, or for those who take advice and recommendations dearly to heart, our gardens can quickly become perplexing, overwhelming and not fun.
So, let me say from the outset of this post, that (in my humble opinion) the greatest risk we run when seeking to diagnose nutrient deficiencies in our gardens is not that one of our plants will die, or even that a hundred plants will die and our entire garden will be sapped of nutrients and perish. It’s that the internet with all of its advice, recommendations and warnings will slowly sap our own joy of gardening, reducing us to panicked (indoor) researchers of ‘yellow spots’ ‘green veins’ and ‘discoloured leaves’.
If that sounds at all like you, stop reading. Make yourself a cup of tea. Put on a hat. Go outside. Find a spot in your garden where something is flowering, or where an insect is hovering, or an earthworm is burrowing and just sit there. If there are birds singing, listen to them. Forget all about discoloured leaves. In the grand scheme of things it is far more important to enjoy your garden than to fix every single ‘problem’ that befalls it.
The undeniable truth for all gardeners (whether they like to admit it or not) is that some plants just die. Caring for living things is an imprecise art, and when you throw fungus, insects, temperature, moisture and soil into the mix it becomes more imprecise still. The truly heartbreaking thing isn’t when a couple of plants die, it’s when a combination of bewilderment, frustration and an unfounded sense of incompetence causes people to put away the trowel, call themselves ‘brown thumbs’ and abandon gardening.
Something worth mentioning at this point is that - so far - none of the information you are about to read has had any real impact on how I’ve gardened, ever. Because for the majority of the time I have been working in my garden I didn’t know any of it. I began my garden mid-way through my PhD when I was already forcing myself to read data analyses sections of peer reviewed papers; toothpicks prising my eyelids open to keep me from falling asleep, teeth grinding to a paste in my mouth, hair falling out with bored frustration at endless acronyms and graphs I couldn’t comprehend. Ok, maybe it wasn’t that bad, but I certainly had no patience or mental capacity to add more dry, specific or finicky information to my brain. The garden was a reprieve from all that, somewhere to simply experiment and tinker. Instead of learning about how phosphorous and nitrogen differentially affect plant growth, I developed a deep love and attachment to the experience of gardening itself. Do that first and you’ll end up learning all the same stuff eventually anyway, but it will be based on a bedrock of pure enjoyment and that will absolutely last you a lifetime.
So. Now. If there’s any chance you’ll start looking at your garden with the eye of a GP diagnosing a hundred ‘problems’ and forgetting what you loved about it in the first place, here is the short version of avoiding nutrient deficiencies. This is all you really need to know/do/add for a 97% healthy, happy garden with plenty of nutrients for your plants:
If your soil is sandy, add clay.
If your soil is heavy and clay-based, add sand or grit.
Regularly add well-rotted animal manure to your garden (sheep, pig, cow - all great). Go for it - add HEAPS, it is very hard to overdo.
Add a thick layer of mulch (preferably lupin or pea straw, as they also help to fertilise your garden) at least every spring and preferably every spring, summer and autumn.
If you have a worm farm or a compost tumbler - so much the better, chuck all that in too.
And if you live in Perth (or any other region with neutral-to-alkaline soils) and you want to grow blueberries (or other acid-loving plants like azaleas, gardenias, rhododendrons etc.) but they just aren’t thriving, stick them in a pot with good quality potting mix and add pine bark mulch to acidify the soil - don’t even try to get them to grow in sandy, alkaline garden beds. Almost everything else should be pretty happy with manure, compost and mulch.
And that’s it. That is exactly what I have done - and basically all I have ever done - for the last 6 years, and no terrible disaster has befallen the garden. If you want to you can absolutely just stop reading here, follow that advice and your garden will be pretty damn good.
If you have alkaline soil it’s best to grow blueberries (and other acid-loving plants) in pots
Now that that’s out of the way, if you promise that you’re just curious and you also promise to relentlessly enjoy your garden no matter what, then by all means fill your brain with all the nutrient deficient info that follows.
Nutrient deficiencies - the basics:
Essential nutrients for plants:
Plants, like humans, require various nutrients to thrive. Some of these nutrients they need in larger quantities (primary macronutrients), some they need in moderate quantities (secondary macronutrients), and some they only need in trace amounts (micronutrients).
Primary macronutrients are the big three: nitrogen, phosphorus and potassium
Secondary macronutrients include: calcium, magnesium and sulfur
Micronutrients include: boron, chlorine, copper, iron, manganese, molybdenum and zinc
Plants can become nutrient deficient for a variety of reasons:
The soil may lack adequate nutrients for the plant to absorb
The soil may be too dry (plants need water to facilitate nutrient absorption)
The soil may be too wet (overwatered plants can get root rot, inhibiting their roots’ ability to absorb nutrients)
The soil may be too acidic (low pH) or too alkaline (high pH), making the nutrients in the soil less ‘available’ (more on what that actually means in a sec). Ideally, your soil will be neutral (pH 7) to slightly acidic (pH 6-6.5).
The soil may be very sandy and free draining, meaning nutrients are easily washed away
The plant’s roots may be damaged or underdeveloped, hindering its ability to absorb nutrients
Identify the underlying cause of a nutrient deficiency:
Before amending your soil or attempting to address a nutrient deficiency in your garden, it’s important to work out what the underlying cause of the deficiency is. Is your pH too high or too low? Are your plants receiving too much water or not enough? Is your sandy soil allowing nutrients to drain right through, or are insects or fungal diseases damaging your plants (which may result in root damage or may simply give the plant the appearance of nutrient deficiency, when really something else is at play)?
Soil pH & nutrient absorption:
If you’ve been adding piles and piles of manure, fertiliser, mulch and trace minerals to your soil but still have plants showing all the signs of a nutrient deficiency your problem may actually be soil pH. It’s possible to have a very nutrient rich soil, but if that soil is also highly acidic or highly alkaline these nutrients will not be chemically ‘available’ to the plants.
Understanding why requires a little chemistry.
So, what you need to know first is that soil pH is measure of how many positive hydrogen ions (H+) and how many negative hydroxyl ions (OH-) are present in your soil. A positive ion is a particle that has lost an electron (electrons have a negative charge, so losing an electron means the particle ends up with a positive charge). A negative ion is a particle that has gained an electron (giving it a negative charge).
Charged particles attract other charged particles, and opposites attract. So, positively charged particles attract negatively charged particles, and negatively charged particles attract positively charged particles.
Why is this important? Well, charged particles have a habit of interacting with other chemical compounds and changing them in various ways. In our soils, this includes the chemical compounds (i.e. nutrients) that plants need to survive. This means if we have lots of charged particles running freely around in our soil (to the extent that a charged particle is capable of ‘running’) there’s a greater likelihood that they will interact with the other chemical compounds in the soil, sending things a little out of whack.
This is where our soil pH comes in. Recall that soil pH is a measure of how many H+ and OH- ions are present in our soil.
Basically:
More hydrogen (H+) ions = more acidic soil = pH less than 7
More hydroxyl (OH-) ions = more alkaline soil = pH greater than 7
Equal proportions of hydrogen and hydroxyl ions = neutral soil = pH of 7
When we have neutral soil (i.e., an equal proportion of H+ and OH- ions), the H+ and OH- ions are balanced and so aren’t looking for other chemical compounds to mess around with. But in acidic or alkaline soils, the H+ and OH- ions are out of balance, and so some are free to interact with the other compounds in the soil. In many cases, these interactions cause the nutrient compounds to ‘precipitate out’ of the soil, turning them from dissolved compounds into solid materials that the plants can’t absorb.
This is why both acidic and alkaline soils can affect the ‘availability’ of other nutrients in the soil, and depending on whether your soil is acidic or alkaline, different nutrients will be affected. Generally speaking, more nutrients are available in neutral and slightly acidic soils (pH 6-7). On the other hand, if your soil becomes too acidic some nutrients will lose availability and the micro-organisms in your soil will not function as well. As in all areas of life, the key seems to be balance.
Red fleshed apple doing just fine in slightly alkaline (pH ~8) soil
What to do about soil pH:
What do you do if your soil pH isn’t neutral? here are a few things to consider:
First, don’t worry too much about it, because there’s not that much you can do anyway! It’s almost impossible to permanently change the pH of your soil. Take Perth, for instance. Most of our coastal gardens are built on sandy soil with a limestone bedrock. This means our soils - by default - tend to be sandy and alkaline. Thinking you can permanently change the underlying structure of your soil is like sprinkling coco on a freshly baked lemon sponge and expecting it to turn into chocolate cake. We just can’t make that much of a difference.
The good news is, we absolutely can change the topsoil in our gardens with regular additions of mulch, manure and other organic matter (e.g., compost). As these organic materials decompose, they create a rich topsoil layer of humus, which acts as a protective barrier against extremes of pH and keeps the microorganisms in your soil safe as well. Keep this layer moist and replenish it often, and you’ll go a long way to providing your plants with the nutrients they need.
Some people decide to take more drastic measures to change the pH of their soil (i.e., adding things like aluminum sulfate or sulfur directly to the soil). Adding an acidic mulch like pine bark mulch is also an option (although it works more slowly). These methods can all work to lower pH for a time, but it’s also easy to overdo it by adding too much and sometimes you can end up doing more harm than good (for instance, if too much pine bark mulch is added at all once it can impede some plants’ growth).
Clematis - a beautiful climbing plant that tolerates alkaline soils
Native hibiscus - planting natives is a great way to ensure they are suited to your soil type.
The bottom line
Ultimately, the best (and simplest!) advice I have is:
First, give your garden a great layer of topsoil with plenty of mulch and manure. This is almost impossible to overdo and are fantastic for overall plant health.
Second, if you find out you have soil that is a little acidic or a little alkaline, simply focus on growing plants that suit that environment. After all, there are very few places on earth for which no plants have adapted to thrive. There are plants that love acidic, clay soils, and just as many plants that love sandy alkaline soils. Here are a few recommendations.
Plants that love acidic soil: (i.e., all the plants I’ve killed at least once) blueberries, azaleas, rhododendrons, holly, gardenias, cranberries, begonias, magnolias, pelargoniums, hydrangeas, potatoes, gardenias (you can find a nice long list here).
Plants that love alkaline soil: dusty miller, yarrow, geraniums, clematis, coneflower, daylily, honeysuckle, hosta, salvia, sweet peas, lavender, thyme, parsley, oregano, asparagus, sweet potatoes, beetroot, cabbage, okra, cauliflowers, cucumbers, celery, barberries, juniper, lilacs, and oleanders (for a longer list, see here). From my experience in my own garden (pH ~8) I’ve found a heap of other plants also do well, among them Californian poppies, Flanders poppies, breadseed poppies, Artemisia (aka wormwood), dogbane, sea lavender (aka statice), borage, calendula, brassicas, fennel, daisies and butterfly bush.
Note: From these two lists it might look like there are more plants that tolerate alkalinity than acidity, but this is actually just a reflection of the fact that my garden is slightly alkaline. If your garden is slightly acidic there will be heaps more that you can grow successfully. The key is to be willing to experiment - find what works in your garden, and keep planting it!
Flanders poppy
Californian poppies
Breadseed poppy
Most importantly, if you’ve tested your soil and found a pH in the range of 6-8 don’t freak out. For most plants, soil somewhere within that range is absolutely fine (I think mine is around 7.5-8), so the last thing you need to do is start throwing lime or sulfur into your garden beds. If your plants look healthy they probably are and it’s usually much better to do less than more.
While changing the pH of your ENTIRE garden FOREVER may be out of the question, you can still address nutrient deficiencies in your plants in a number of ways. The first step is working out what nutrient is deficient… But I’m afraid that is going to have to wait for part II (I know, I know, MASSIVE cliffhanger!)
Sorry to leave you hanging like this, but this blog post definitely qualifies as a two-parter. Don’t worry though, I’ll be back! Tune in next week to learn all about dark veins, yellow flesh and burned spots (how sexy!)
Until then, happy gardening!
Xx Casey
