There is something strange that happens to us when we walk around in the garden work. Whether it’s a weekend garden warrior or an after-work gardener, we know intellectually that you can’t rush a good garden. But there seems to be an overriding urge among all gardeners who just want the plants to go on and grow.
And this is where all reason jumps overboard and leads otherwise smart people to do downright stupid things.
You don’t know where I’m coming from? Have you ever heard the saying, “if an ounce is good, a pound is better?” Have you ever fallen victim to its driving forces? No matter how hard we try, plant fertilization is where the identity of gardening trumps the superego without the intervening logic of the seasoned, all-knowing garden Zen master ego.
Basically, plant fertilization is a pretty basic thing. There is a list of chemical nutrients that all plants need to grow and reproduce effectively, and more importantly, to look fabulous in the garden. Our job is to make sure our plants have an adequate supply of these nutrients when they need them. Pretty basic stuff.
Now, we all know that when one or more of these essential nutrients drop below their optimum level, plant performance suffers. When we add more of this limiting element, plant performance improves. But we also know very well that the curve of increased growth with increased nutrient availability eventually flattens. And when we reach a certain point, a further increase in nutrient level can dramatically reduce plant performance.
Although there are many signs of nutrient deficiency which can vary widely, they generally follow a consistent pattern; reduced vigor, gradual loss of greenness, yellowing of leaves (usually in the center) and reduced flowering/fruiting. If fertilizer/nutrient levels are too high, you may see reduced flowering/fruiting (a particularly common problem with nitrogen on fertilization), yellowing/browning along leaf edges, and loss of root tissue . It seems logical – except for that pesky superego – that we instinctively pull towards the middle of the road.
To make things a bit more confusing, different types of plants require different levels of nutrients for optimal growth. Tropical plants and annuals that sprout tons of soft green growth each season tend to do better with higher fertilizer levels. You want giant cannas or massive elephant ears, give them plenty of fertilizer. Woody trees and shrubs occupy the opposite end of the spectrum, doing much better with lower fertilizer levels. Herbaceous perennials are a bit more varied but tend to fall somewhere in the middle.
The trick with fertilizers is to come up with a recipe that not only has the required nutrients at the correct level, but to make sure those nutrients are available to the plant when needed. This requires you to choose the right nutrient source, apply it in the right amount, at the right time, and hold it in the soil until it is needed. Each of these points represents an opportunity for the identifier to be crushed by its more exuberant cousin.
The most commonly used garden fertilizer comes in the form of soluble salts, the blue juice you form by first dyeing your fingers blue, then your jeans, then the driveway…and finally the watering can. . It’s relatively easy to mix, inexpensive to buy, and works well for plants that need readily available soil nutrients.
Soluble fertilizers are good for annuals and tropical plants planted in containers or in flower beds. The nutrients are immediately available, which is good. The problem is that they are easily washed out of the pot or the ground. These leached nutrients, whether from excess water or a downpour right after fertilization, run down the driveway, into the storm drains, and eventually into the creek down the road. Not a good situation.
Slow-release granules are kind of like solubles but they dissolve slowly, releasing their nutrients a little at a time. You don’t get as big and fast a kick, but you lose a lot less in the sewers. These are a bit pricey but they are very effective. We like to mix in slow-release fertilizers in our container planting mix and annual beds to reduce the need for soluble fertilizers.
Finally, there is the compost. For many plants, especially woody and most herbaceous perennials, the annual application of organic composts is the perfect nutrient recipe. They have low levels of nutrients that are released over a nice period of time. They are also very effective in improving soil structure, erosion resistance and moisture retention during periods of drought. Composts alone don’t provide enough nutrients for high-potency tropicals and annuals, but combined with the occasional addition of soluble fertilizer, they do a great job.
And when it comes to keeping that oversized super self in check, remember another old garden adage – an ounce of prevention is better than cure!
Yew Dell Botanical Gardens is located at 6220 Old La Grange Road, Crestwood, Ky.