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Lilac General Care

Planting
Lilac trees will do best when planted in the fall, as this allows the tree to establish a good root system before it flowers in the spring. They are known for their rapid growth, and once it has been in the ground for 4-5 years, it will grow from a shrub size to a tree size.
Lilac trees should be planted in an area where they will get full sunlight, a minimum of 6 hours each day. Less sunlight and the flowers will not bloom as fully in the spring, and shade encourages powdery mildew. Make sure that your Lilac tree will have enough room to grow, as their canopies can reach up to 12 feet wide.
Adding 3-4 inches of mulch around the base of the Lilac will help to retain moisture and help keep weeds from growing.

Soil Information
A good-draining soil is necessary for Lilac trees as they require moist but not soggy soil. A good rule of thumb is to dig a hold 12 inches deep and 8 inches wide. If it drains within an hour after you fill it up with water, your soil is in good condition for housing a Lilac tree. Lilac trees also like alkaline soil that is rich in humus. You can increase the alkalinity of your soil by applying wood ash or garden lime after testing and seeing that the pH levels are not correct.

Watering
You should irrigate your trees instead of watering from above, as the roots are what mainly need water.
During the spring, it is recommended that you water your Lilac tree every 10-12 days until the flowers are completely bloomed. From there, whenever the top of the ground is dry, you can water them. Lilac trees prefer deep, infrequent watering.
Young trees cannot survive as well as older, more established trees and should be watered once weekly to ensure the ground does not get too dry. If your leaves begin to wilt, you should water your Lilac.

Fertilizing
Lilac trees should be fertilized when planted with a balanced tree fertilizer. After the 2nd or 3rd year, you can use an NPK ratio 10-10-10 once a year in the springtime. Bonemeal and fireplace ash over the root area will keep the alkalinity of the soil balanced and help blooming in the spring.
However, if you fertilize too late in the season, you could run the risk of bacterial blight.

Pruning
Lilac trees should be prunes in the late spring or early summer, after the tree is finished blooming. This ensures that the next year’s buds have plenty of time to grow. However, if you prune too late, you may chop off the buds that are for the next year’s bloom.
Start by looking for suckers, which are small shoots that grow around the bottom of the trees. You should trim them down to the ground, then remove the dead and dying flowers to their stems. This encourages blooming since it removes the dead parts. If you want to keep your Lilac tree shaped a certain way, cut back 1/3 of the branches. Air circulation can be increased by cutting internal branches.

Pests
One of the main pests attracted to Lilac trees are Lilac Borers. These are caterpillars that eat the wood parts of the tree. They leave behind small piles of sawdust, small holes left behind in branches, and leaves turning yellowy. These can be removed by cutting off affected branches and spraying your Lilac tree with an appropriate insecticide.
Leaf miners are small yellow and black flies that do not grow any longer than a few millimeters. They lay larvae that tend to mine down into the leaves, causing damage to them. A close examination of the leaf will show you small, empty tunnels left behind by the leaf miners, with dark larvae visible at the end of said tunnels. One solution is Neem oil, which slows the leaf miner down and keeps them from continuing to tunnel, mating, and flying around. This will not remove them completely and immediately, but continued use will cause them to die out. Make sure to spray both top and bottoms of leaves. White oil will do the same as the Neem oil, and is made by using 1 teaspoon of vegetable oil, 1 teaspoon of dish soap, and just under 500mL of water. Mix well and spray a light, even coat on tops and bottoms of leaves.
Oyster-shell scale insects will drain the juices from the Lilac tree. These insects live inside the bark, and will leave evidence in the form of dark, gray, rough and bumpy branches. They are small and look like individual scales covered in wax. Sprinkle Sevin dust, wash the bugs off with insecticidal soap, or apply permethrin to the bugs to remove them.

Diseases
Leaving enough room between your Lilac trees will help prevent the most common diseases: powdery mildew and bacterial blight. These can also show up if the weather has been especially damp and stagnant for a while.
Powdery mildew can be removed by using a milk solution.
Bacterial blight will affect the leaves, causing them to turn brown and wilt. Remove these affected twigs, leaves, and flowers and destroy them.