Healthy trees often do not need extra nutrients. Adding fertilizer to good soil can put the nutrient ratio out of whack, causing your tree to overgrow and weaken the wood.
If the rings are spaced out evenly, you probably won’t need to take precise measurements. However, you still may wish to do this to understand exactly how much your tree is growing. A new tree will grow by approximately 9 to 12 in (23 to 30 cm) every year. An older tree will grow by about 4 to 6 in (10 to 15 cm) every year. Depending on the species, your tree will reach maturity within 10 to 30 years. Expect the growth to slow down by then. [3] X Research source
You can also purchase a testing kit at most home improvement stores. Some of these tests may not be as detailed as an official test, but usually the results can help you figure out how to improve your soil. Sometimes the soil’s pH is the problem. This isn’t fixed with fertilizer. Instead, increase the pH with garden lime and lower it with sulfur or aluminum sulphate. However, you should only adjust your soil if it’s not in your tree’s optimal pH range.
Fall is the ideal time because the tree is still active, so it will absorb nutrients and store them for spring growth. If you add fertilizer too early, the tree will continue growing. You may notice new growth that dies in summer or winter, leaving damage on your tree.
Make sure you measure the tree’s trunk at about chest height in order to get a safe estimate on how much fertilizer you need.
For example, a tree 3 in (7. 6 cm) thick needs about 0. 3 lb (0. 14 kg) of fertilizer. 3 x 0. 10 = 0. 3. Areas such as sidewalks, driveways, and buildings don’t count when determining the tree’s growing area. Trees near these structures will need less fertilizer overall. Another way to estimate how much fertilizer you need is to multiply the tree’s age by 0. 10.
For example, if you estimate you need 0. 3 lb (0. 14 kg) of nitrogen in a 30-10-10 fertilizer, you will need about 0. 9 lb (0. 41 kg) of fertilizer. 0. 3 divided by 0. 3 = 0. 9.
Low nitrogen is the most common reason to add fertilizer. If your soil is low in nitrogen, you can get a fertilizer with little to no other nutrients. Look for something with 3 to 12 parts phosphorus and potassium, depending on the composition of your soil. For nitrogen fertilizers, use a slow-release fertilizer. If your soil lacks phosphorus, potassium, calcium, or other nutrients, you can get liquid fertilizer and inject it directly into the soil. General fertilizers for woody plants will have a nitrogen-phosphorus-potassium ratio of 8-1-1 or 15-5-5.
This measurement is the diameter of the branch spread and will give you an idea of how far the tree’s roots have spread.
You can use a drill with an auger attachment to easily make the holes. The holes should reach about 1. 5 times further than the reach of the branches. Drilling holes can help any tree absorb nutrients from fertilizer. It can be particularly useful if you rake up the tree’s leaves or if there are grass and other competing plants above the roots. Most of the roots will be no more than 18 in (46 cm) below the surface, so be careful. Also be aware of any utility lines under the soil so you avoid damaging them. Avoid disturbing the root zone too much. Trees have both large, conspicuous roots and smaller roots in their root zone. Try as best as you can to avoid all of these roots.
If you dug holes to access the roots, fill the holes with the fertilizer.
Compost is low in nitrogen, but it does add more potassium to the soil. Factor your fertilizer choice into the amount of compost you add.
To test the soil, push a screwdriver or metal rod down into the soil. It should come out wet and dirty. If you can’t use a hose, using a bucket or sprinklers can help.
