Fertilizing Irises

by Tom Waters

When I first began growing irises in the 1970s, the standard advice (and it was not new advice even then) was “fertilize with superphosphate and/or a balanced fertilizer low in nitrogen, such as 5-10-10, in spring before bloom and again in fall”. The advice was repeated everywhere, without reference to climate or soil. This was the heyday of the use of synthetic chemicals in the garden. Every problem, major or minor, had a solution that came out of a bag or cardboard box.

Much has been learned since then that should put a damper of our enthusiasm for synthetic fertilizers. Sadly, however, that knowledge seems to have not permeated very much into the culture of iris enthusiasts. Almost daily, I read the same advice I heard decades ago repeated on Facebook and other discussion fora, still without qualification or any evidence of caution or indeed reflection. People don’t even seem to care whether their soil actually needs phosphorus; they just follow the advice without question.

Have you ever wondered how plant life has flourished on Earth for more than 400 million years before there were factories to synthesize superphosphate? Have you ever wondered how the great gardeners of Victorian England managed to grow irises without plastic bags of fertilizer granules?

A walk in a nearby forest. Funny, these trees have gotten awfully large without superphosphate each spring and fall.

In nature, the nutrients essential to plant growth are perpetually recycled. All plant and animal tissues contain nitrogren and phosphorus and the other essential elements, and as these tissues decompose, soil microbes process them through stages until the nutrients are once again accessible to the roots of growing plants. Recently, we have become more and more aware of the complex ecosystem of bacteria, fungi, and small plants and animals that exists in healthy soil, and the role they play in sustaining the larger plants and animals that live above ground. Plants on Earth have evolved in conjunction with soil life to make the most use of the natural processes by which nutrients are recycled. Have you heard of mycrorrhizal fungi? These soil fungi exist in symbiosis with plant roots, extracting and processing soil nutrients for the plants in exchange for carbohydrate food which the plant produces by photosynthesis. They can increase the nutrients available to plants more than a hundredfold. This is but one example of the complex interaction between plants and the soil life that supports them. Soil organisms provide many other benefits to plants, such as reducing susceptibility to pathogens.

If nutrients were not recycled through living soil ecosystems in this way, every spot of Earth would become completely barren of life in a short period of time.

This handful of soil contains billions of microorganisms - more microscopic living creatures than there are human beings on Earth.

Feed the Soil, Not the Plants

Synthetic fertilizers bypass this natural process of nutrient recycling in the soil, essentially giving the plants a direct injection of specific nutrients, such as nitrogen or phosphorus. This can be very effective in producing growth, especially if the amount of nutrients available naturally through the soil is small. The agricultural revolution of the twentieth century was made possible in large part by supplying additional nitrogen and phosphorus in this way, thus increasing agricultural yields even in poor soils. But is there no “down side”?

The first potential problem with synthetic fertilizer use is that it affects everything in the soil, not just the plants you grow. All the soil microorganisms now find themselves in a radically different chemical environment, one they are not evolved to deal with. The additional nutrients can cause a population explosion in the microorganisms, which then devour every bit of organic matter in the soil. With the organic matter (their food source) gone, the microorganisms die off, leaving a soil without organic matter and without much life. The plants you grow have gotten their quick boost of nitrogen or phosphorus, and you can pat yourself on the back at how big and green they have become, but beneath your feet the web of life that supports them has been damaged or destroyed. As Tony Avent of Plant Delights Nursery explained, “If all you ate were Snickers bars, would you get larger? Absolutely! No question! You would get dramatically larger. But would you be healthy? That is the difference.”

Once the soil ecosystem has been damaged or destroyed, the synthetic fertilizer “boost” becomes an addiction. Without a healthy soil ecosystem, the plants now need the regular application of synthetic nitrogen and phosphorus to provide what the soil would otherwise provide naturally. The garden is now essentially an experiment in hydroponics, with the soil merely anchoring the plants in place as you wash solutions of chemicals past their roots.

Organic gardening uses an approach that seeks to enhance the natural nutrient cycling process, rather than bypass and cripple it. By building your soil with compost or other organic matter, the soil life builds up in a sustainable way. The organic matter not only provides the nutrients needed by the plants and the soil life, but also provides that soil life with the carbon-rich organic matter that is its food source. You thus secure not just the short-term benefit of a nutrient injection, but the long term benefits of healthy, living soil.

Nutrient Pollution

That might be enough to make a thoughtful person reconsider reliance on synthetic fertilizer. But there is more. Waterways in the US and indeed all over the world are being destroyed by synthetic fertilizer use, through a process called eutrophication.

When excess phosphorous or nitrogen applied to farms, lawns, and gardens makes its way into streams and lakes, the nutrients create a population explosion of algae that quickly consume available food and and block sunlight, depriving the water of oxygen and choking out the other water life. (Sound familiar? It is not dissimilar to what happens to the soil life when you saturate them with nutrients.) About half our lakes now suffer from eutrophication. The situation has become so severe than eleven states have enacted bans on phosphorus fertilizers. These bans all have various exceptions, so you may not be restricted from spreading superphosphate on your irises, depending on where you live. But it should give one pause for thought. If the environmental damage caused by phosphate fertilizers is becoming so severe that legislatures are trying to stop it, do we really need to be adding to the problem in our home gardens? [For an excellent summary of the history of phosphate fertilizer and the problems it causes currently, check out this episode of the Gastropod podcast.]

Climate Change and Sustainability

Fossils fuels are essential to the production of synthetic fertilizers, nitrogren and phosphorus fertilizers both. We now know that the Earth is plummeting rapidly toward higher global temperatures, faster than ever before in the geologic record, and faster than life can adapt. The Permian extinction, which eradicated 90% of life on Earth, was triggered by a global temperature increase of only about 5 degrees Celsius. We need to think of a better way of meeting our agricultural and horticultural needs, very soon.

The nitrogen for synthetic fertilizers comes from the atmosphere, but the phosphorus must be mined and extracted from minerals. This is a finite resource, and it is already under stress. We need to return to the natural process of recycling the phosphorus that is already incorporated in plant and animal tissues, rather than extracting the last reserves from the ground and poisoning our lakes with excess run-off.

Fertilizer Advice for the 21^st Century

So if the advice from fifty years ago is so problematic, what is one to do? Here is how I answer the question of how to fertilize irises.

1. Build your soil. Add lots of organic matter. Compost is the form closest to what the plants can use, but even partially decomposed organic matter will benefit the soil. Not only will you be providing nutrients and encouraging your soil life, but you will be improving the soil’s structure, too. Soil with organic matter mixed in holds both air and water better, and has improved texture. This is a win all around. Keep this up.

2. Observe your plants. If you’ve been building your soil for several years, chances are your plants will be healthy and getting what they need. You’ll have Earthworms and insects enjoying your soil too. Now go have a lemonade. Most gardeners will never have to proceed to the following steps.

3. Identify the problem. If there is a problem, figure out what it is. If your plants still seem sickly or fail to thrive, have your soil tested. Don’t just guess and dump things on your soil, because an advertisement or someone on the internet says a particular product will work miracles. This can do more harm than good.

4. Research solutions. If your soil really is deficient in a particular nutrient, despite all your soil building work, investigate the options for addressing the deficiency. There are organic sources for most nutrients, and those are to be preferred.

Yes, they do bloom. This bed was planted eight years ago. No synthetic fertilizers have ever been used.

And Finally…

These are messages that not everyone is receptive to. I understand. I started gardening in a time when following that old advice just meant you were a good gardener. Now, it has come under criticism, and some of those criticisms seem to carry moralizing overtones. I, like many other advocates of organic gardening methods, have a certain passion about the subject. But that does not mean I expect everyone who reads this to have some kind of religious conversion and abandon their evil ways. Rather, my goal is more modest. I’d just like to see all iris growers study a bit. Learn a bit about soil. Learn a bit about fertilizer pollution. Learn a bit about organic methods. Then follow up with making a few new choices you are comfortable with, and try them out. Then see what your irises have to say.

Growing Irises Organically

by Tom Waters

Today, I thought I'd write about organic gardening methods, particularly my experiences of them as an avid iris grower. When I first took up growing irises in the 1970s, organic gardening was still very much a fringe movement. Storage sheds full of bags of synthetic chemicals intended to address every conceivable gardening problem were the norm.

Today, organic gardening has become mainstream. Most modern gardening books emphasize organic practices, and many people are excited about having gardens that resemble nature and use nature's own cycles and processes. This post is not meant to be polemical. Rather, I'm just hoping to provide some starting-off points for people interested in using more organic methods in their own gardens.

Fertilizer

When I began transitioning to organic gardening methods in the 1990s, I was relatively unconcerned about synthetic fertilizers. A fertilizer is not a poison after all. And what difference does it make if the nitrogen a plant needs comes from a factory or from a compost pile? Nitrogen is nitrogen, after all. But a lot has been learned about the negative effects of synthetic fertilizers in recent decades. The processes used to synthesize nitrogen and phosphorous fertilizers depend on petroleum, and so are not sustainable and contribute to greenhouse gases in the atmosphere. Furthermore, fertilizer runoff has created an enormous problem: eutrophication of our lakes and waterways, causing ecosystem destruction on a huge scale. Granted, home gardeners are not the main culprits in this problem, but why should we be adding to it if we don't need to?

despite rumors to the contrary, irises do grow and bloom
without the use of synthetic fertilizers

Beyond all these considerations, our understanding of soils has progressed tremendously since the mid-20th century. A healthy soil is an ecosystem unto itself, harboring extraordinary numbers of decomposers, from earthworms and beetles down to micro-organisms and fungi. All these creatures process waste matter into nutrients that plants can use, creating a self-renewing reservoir of the ingredients plants need to thrive. A blast of highly soluble nitrogen or phosphorus from synthetic fertilizer can completely disrupt the chemical environment in which the soil organisms live. The instant "boost" the irises get from the synthetic fertilizer comes at the expense of destabilizing the soil ecosystem over the long term.

Consider doing nothing. Beginning iris growers are often told something like "fertilize with superphosphate or a low-nitrogen fertilizer such as 5-10-10 before bloom in spring and again in fall." So common is this mantra, that people often do not even step back to consider why fertilizing is necessary at all. There have been flowering plants thriving on the Earth for the last 160 million years or so, and petrochemical-based fertilizers have only been around for about a century. So obviously they are not needed - in the big picture of things, at least. Irises will grow and bloom almost anywhere their water and sunlight needs are met. My advice to beginning growers is to not worry about fertilizers unless your plants appear unhealthy. And then, have a soil test so that you know what exactly is deficient. Then, look for organic methods to supply the deficient nutrients.

The virtues of compost. Compost is the single most important thing you can do for your soil. If improves soil texture, helping to capture air and water which plant roots need. And it feeds all the decomposers and other organisms that make for a healthy soil ecosystem. Even better, it does all this almost irrespective of what type of soil you are starting with. Everyone should have a compost pile. But remember its main virtue is as a soil amendment; it must be added in volume to make much of a difference. Composting your kitchen scraps is not going to produce enough compost for a whole garden. You can buy compost from commercial sources. You can also collect leaves and other vegetation waste to compost. Animal manure is also an excellent compost ingredient.

There are various other organic products intended to provide specific nutrients, such as cottonseed meal, alfalfa meal, bone meal, blood meal, and so on. These provide organic alternatives to some of the synthetic fertilizers. But as with synthetics, it makes sense to do your homework and learn if the specific deficiencies these products address really apply in your case.

A final thought: A boost of synthetic fertilizer can indeed create visible effects quickly. You might get taller stalks and larger flowers, for example. Putting synthetic nitrogen on your lawn can make it look noticeably darker and greener a week later. But these effects do not mean that the synthetic fertilizer is improving the overall health of your irises, or your lawn. Health requires more of a focus on the long term.

Weeds

weed or wildflower?

One well-known herbicide is the focus of controversy everywhere you look these days. I don't intend to engage that particular debate here, as it would quickly take on a life of its own and distract from the bigger picture of organic gardening practices, which is the subject of this post.

I find that weed control represents most of the labor involved in my garden. It's a huge task, much more laborious and time-consuming than watering, soil building, grooming, planting, dividing, and all the rest. I think most gardeners' experience is comparable, wherever they live.

Consider doing nothing. That sounds ridiculous, but let me explain There's two parts to this suggestion.

(1) Consider not using any herbicides at all. I remove weeds from my iris beds mechanically (pull them out). This is really the only way that is 100% safe for the irises and other desirable plants in the garden. And although it is a lot of work, it does have the bonus of keeping you familiar with how every square inch of your garden is doing. I couldn't do it without my handy padded kneeler, but at present I can more or less manage. Having said that, I do understand that there are many people who would have to give up gardening entirely if hand-weeding were the only option.

(2) Consider what needs to be removed, and what doesn't. In recent years, I've become very interested in native plants, and it has changed my philosophy of gardening. Certainly, there are some plants that will absolutely overrun a garden if left unchecked. But there are others that are really only a problem in the eye of the gardener. Originally, I ruthlessly pulled everything I didn't plant. Now, I know all the regular interlopers individually, and I pull things that I specifically know to be problem species. Some other natives (and self-sown garden plants) get to stay if they are in a place where they will not cause serious harm, Native plants in the garden help "tie it in" to the surrounding landscape, and provide benefits for local wildlife. They are also inherently adapted to the environment, reducing water needs and other types of care for the garden as a whole.

Understand what you use. If you do decide to go the herbicide route, there are certain questions you need to answer in making your selection. This is just as true for organic or "natural" herbicides as for others. (1) What does it do? Does it just kill top growth, or does it get the roots of perennial weeds? (2) How harmful is it for humans, pets, or wildlife? (3) Does it damage the soil? Some popular "recipes" for making herbicides out of household products circulate on the internet. Just because you can find something in your pantry doesn't mean it's "harmless" in the garden. Do the research.

This year, I've been using a commercial product that is a mix of highly concentrated vinegar, orange oil, and molasses. It's very satisfying to use, as it burns off top growth almost instantly. It does have limitations, though: it really needs sunlight to act fully, and it only kills the leaf surface that it actually lands on. This means the to completely kill a plant, you need to apply a lot of it. And of course, it has no effect on roots. I have extremely alkaline soil, so I'm not worried about the effects of the acid - that might be different if I lived where soil was too acid to begin with. It's useful stuff, but not suitable for all jobs.

Pests

The dangers of chemical insecticides have for decades given great impetus to the organic gardening movement. Things presumed safe by one generation of gardeners are later understood to be dangerous and taken off the market.  It's not surprising that some people just want to stay clear of all of them.

Today, people are also just more aware of the shortsightedness of introducing poisons into the environment we share with other plants and animals, even if there are no direct consequences for us humans.

But most every gardener at some point or other has experienced an insect infestation that has gone completely out of control.

'Dollop of Cream' with chives

Consider doing nothing. It's not necessary to react to every insect sighting or every sign that something has been nibbling on a leaf or two. In most places, in most years, there is an ebb and flow between pests and their predators; nature can be wonderfully self-correcting. Garden planning is an important too, as well. Pests tend to exploit monocultures. The more different kinds of plants you grow, the less likely you garden is to become a beacon to one particular pest species. Some plants actively repel certain pests. Aphids don't like alliums, for example. I have not had the tiniest aphid issue since I studded my garden with clumps of chives.

Now this has gone too far! Sometimes, though, doing nothing is not an option. Organic controls fall into two broad groups: predators (ladybugs, for example) or species-specific parasites/diseases. As I write this, I am in the midst of grasshopper infestation of Biblical proportions. All 150 iris seedlings I lined out this spring were killed in a matter of days. A friend recommended Nolo bait, a parasite that eventually spreads through the grasshopper population. It's not instantaneous, but works gradually over months, sometimes requiring further application the second year.

local fauna or evil incarnate?

A little research on the internet will turn up a range of organic solutions to most gardening problems. One of the things we give up when going organic however, is instant gratification. Organic methods are not about the quick fix, but about putting things in place now that will reduce problems in the future.

I know that for some people, the choice to use or not use organic gardening methods has a political dimension. For myself, I am more motivated by a passion for the natural world, the great diversity of life, and a love of growing things. When I use organic methods, I feel like I'm learning how nature works and gardening with nature, participating in the great web of life rather than battling with it.

Do you use organic methods in your garden?