Thuja Green Giant is certainly a fast-growing tree, and will grow happily in many different soil types. The natural rate of growth is influenced by the soil conditions it grows in, as well as the amount of light it receives, and these are not things that can be altered, but we can greatly influence the growth of this tree by using a fertilizer program, and selecting the best fertilizer to use.
Plant Nutrients
There are three main minerals needed by all plants to grow, and these are also needed by your Thuja Green Giant plants. The most important for evergreens is Nitrogen. This nutrient makes proteins, and especially chlorophyll, the green molecule that turns sun-light into plant, and gives your plants that healthy green glow. The second important nutrient is Phosphorus, which helps the tips of both roots and shoots develop and grow strongly. The third important nutrient is Potassium, which creates the pressure inside plant cells that holds the softer parts like leaves up in the air. It also makes thick cell walls that resist pests, diseases, and cold damage.
Another important nutrient for your plants is Iron. These helps make those chlorophyll molecules and gives you plants a rich green color. It is especially important if you garden on lime soils. Almost all blended fertilizers contain some iron.
Reading the Fertilizer Packet
All three of these nutrients are needed, but your Thuja plants especially need lots of nitrogen to make them grow fast, strong, and give them a healthy green color. On a packet of fertilizer you will find three numbers, looking like this: 15-19-5. The numbers will be different, and they don’t add up to 100, or any other particular number at all. The first number is nitrogen, the second is phosphorus and the third is potassium.
For your Thuja Green Giant plants you need a fertilizer that has a high first number, and the other two should be equal or lower than that nitrogen number. Numbers like 10-8-6, or 15-5-10, or 20-20-20 are all good formulas to use. Most soils in North America have plenty of phosphorus (the second number) so that one is not important at all in making your choice – it can even be ‘0’. Especially in late summer and fall, a high third number (potassium) is good for winter protection in colder areas.
To check if there is iron in the fertilizer, look for the letters ‘Fe’, which is the chemist’s abbreviation for that mineral. You will probably find a bunch of other nutrients in small quantities as well, and they all help the health of your plants.
What Type of Fertilizer should I Use?
There are three main types of fertilizers sold for gardens:
Water-soluble Fertilizers
These are the kind where you add a few teaspoons to a watering can of water, or put them in a special mixer that fits on the end of your hosepipe. They are great for producing quick growth, especially in newly planted trees with small root zones, so they are a good choice for the first season or two. However, they have to be made dilute, so as not to burn the roots, so they don’t last long in the soil, and they need to be applied every few weeks. It makes sense after that first season to switch to another type that is easier to use.
Granular Fertilizers
These look like fine gravel, often with grains of different colors, and they are either mixed into the soil when planting, or scattered over the surface around established plants. A great idea when planting is to use a fertilizer with a high middle number (phosphorus) to stimulate root growth in your young plants. This should be blended into the soil as you prepare the planting area. The nutrients will be released over a period of weeks, so you get slow and steady feeding for your plants.
Slow-release Fertilizers
These also look like gravel, but normally they will all be the same color. Most of the fertilizers of this type are a blend of nutrients wrapped inside a coating material, which allows them to be released over a long period – often several months. They are usually more expensive, but since you only need one application a season they are great for a low-maintenance garden.
Fertilizer Spikes
These are fertilizer shaped into a spike which is gently hammered into the ground. They slowly dissolve and feed your trees. Be careful to follow the recommendations for the spacing and number to use, and always put them well away from the trunks of your plants.
How and When to Fertilize Thuja Green Giant
The best time to feed your plants is in early spring, just before the new growth begins. This is after the risk of hard frost is mostly gone and the days are becoming a little warmer – what month exactly will depend on where you live. Always follow the directions on the packet to know how much to use per plant or per square foot. Too much fertilizer is worse than none at all. Spread it evenly over the area beneath your trees, and include the area a couple of feet further out as well, which will be where the active, growing roots are. If you are using a water-soluble feed, apply plenty and let it soak down into all the root zone.
Water-soluble solutions should be re-applied every three or four weeks throughout the growing season. Granular fertilizers usually need re-applying in early summer and again in early fall. Slow-release formulations and spikes only need to be applied in spring.
Avoid fertilizing your trees during hot, dry weather, or water them thoroughly after putting down fertilizer.
It doesn’t matter much which kind of fertilizer you choose to use – it only affects the method and frequency of application. Whatever you choose, a good fertilizer program for your Thuja Green Giant trees will make sure you have the fastest-growing and healthiest plants around.