Fertilizer Spikes Are Easy To Use Around Trees, But There Are Downsides

Nothing enhances the look of a lawn like lush, beautiful trees. While sunlight and proper watering are two key ingredients for healthy growth, so is the right mix of nutrients. If your soil is lacking and you want to give your trees a nourishing boost, fertilizer spikes provide an easy way to do so — simply hammer them into the ground and leave them to work. However, while convenient, they do have some limitations. These concentrated spikes only deliver nutrients to roots in their immediate vicinity rather than to the tree's entire root system. Fertilizer spikes may also shatter when hammered into hard soil, which is disappointing since they're typically more expensive than liquid and granular fertilization options.

Broadcast fertilizers are often a better choice for trees since they get absorbed more uniformly by the entire root system, reducing the risk of over-fertilization in specific areas. While this doesn't mean you shouldn't ever choose spikes, understanding how fertilizer spikes work and when you should use them is key to ensuring you don't accidentally cause harm to your tree.

Fertilizer spikes seem like an easy method for delivering nutrients to trees. After installing the spikes, they'll slowly release nutrients into the soil, providing long-lasting fertilization. However, too many nutrients concentrated in one spot may lead to fertilizer burn, which can damage or even kill your tree. Signs of fertilizer burn include weakened branches and scorched or wilted-looking leaves, even if the tree has been adequately watered.

Even when installed properly, fertilizer spikes tend to deliver nutrients to roots in the spike's immediate area instead of the root system as a whole. Installing multiple spikes evenly around a tree's drip line may help prevent over-fertilization, but it's still a risk you take when using this method. That risk may not be necessary in the first place, since most healthy, mature trees won't need additional fertilizer once established.

Another potential problem lies in attracting unwanted insects. Too much nitrogen fertilization can make trees more susceptible to pests, and may even be the reason your plants are covered in aphids. While a small number of aphids isn't usually cause for concern, a large aphid population can turn a tree's leaves yellow and do more serious damage to surrounding ornamental plants.

If you still want to use them despite the downsides, safe use of fertilizer spikes starts with choosing the right nutrient mix. Fertilizers generally list an NPK ratio, which stands for nitrogen, phosphorus, and potassium. The best way to find the proper ratio is to have your soil tested, but you can also choose spikes that are specially formulated for the kind of tree you need to fertilize. Different types have different needs; for instance, you might find that spikes for shade trees contain a larger percentage of nitrogen, while spikes for fruit trees have a more balanced nutrient ratio.

Limit installation of the spikes to the tree's drip line, which is the area on the ground that aligns with the outermost reach of the tree's canopy. A tree's drip line is important in landscaping as this is where you'll find the most absorptive parts of the root system, making it a crucial area for watering and fertilization. Err on the side of installing farther from the tree trunk, since placing fertilizer spikes too close to the trunk can damage or kill a tree.

Manufacturers may recommend hammering the spikes into dampened soil, but you can also prevent breakage by hammering a wood stake into the ground first, pulling it out, and then inserting the spike. Spacing and quantity are also important. Generally speaking, you'll choose a number of spikes based on the tree trunk's diameter, but each product's packaging will have more specific instructions. Evenly space the spikes around the tree's drip line to avoid concentrating the fertilizer in only one area.