JEFF YOUNG, VT MASTER GARDENER
LILAC WORKSHOP
At the Kellogg-Hubbard Library, Wednesday June 20, 2007

Recommended Best book:  Lilacs for the Garden, by Jennifer Bennett

Lilac Culture

1.  Common lilacs need to have 9-12 canes for each 6 feet (in diameter measured at the drip line.

2. Leave at least 2 feet between mature Lilacs. 

3. Plant new shrubs 16 feet apart (circular shape).

4. Allow for a few more canes if you are planting as a hedge with less depth (zigzag pattern).

5. Use the ratio of canes (9-12 per 6’ in dia.) to the space available. Remember to use the drip line as your perimeter. 

6. Determine the canes to be removed or added.
 
7. If too many canes, remove the oldest (tallest) canes first, leaving good spacing between canes.
 
8. If not enough canes, pick one or two of the best suckers each year until there are enough. The best shrub has a good diversity of age among its canes. Leave at least 2’- 4’ of space for mature lilac between house/fence and dripline.

9. Once the lilac is established, consider adding one new cane and removing the oldest cane each year; this will create a vigorous, healthy full flowering plant.
 
10. Lilacs like full sun or at least 10 hrs/day. If sun is limited, sun should be full in the morning. 

11. Avoid excessively windy locations in winter, cold won’t kill a lilac, but the wind will. Lilacs like the summer breeze. Reduce the amount of interior branches to improve aeration. When placing a plant look for what surrounding trees will look like in the future.
 
12. Lilacs don’t like wet feet; they need good drainage, slopes are best.

Lilac Health Maintenance
13. Apply 2” of compost each spring, 18” on either side of the drip edge. 

14. Apply 2” of ground bark mulch each spring from 18” outside of the drip edge toward the center, keep mulch 6” away from any cane. In succeeding years work the compost into the previous year’s compost and mulch, reduce compost and mulch accordingly to avoid a buildup of over 4”. 

15. Lilacs like 7.0 to 7.3 pH, if you suspect the soil has a pH lower than 6.5, do a soil test. Normally, 3-4 cups of pelletized lime for a mature shrub, more if the pH is below 6.5. 

16. Fertilizer should not be necessary, but if the lilac needs a boost after a drought or excessively wet year, use sparingly (2-3 cups) of 5-10-5 or 4-12-8; apply along with the mulch. 
Organic fertilizer, use highest phosphate (middle #) you can find (usually 2-3-3) 

17. #1 reason Lilacs decline is soil compaction. Avoid fertilized lawn to about 2’ outside the drip edge. Avoid heavy foot traffic or lawn tractors to 2-3 feet from the drip edge. 

18. Do not use herbicide (weed and feed) to within 10’ down slope of the Lilac.

19. #2 reason lilacs fail is string trimmer and lawn mower damage. The canes are small; even small bark damage will greatly limit the health of a shrub and weaken the cane making it susceptible to disease.

Pruning
20. Heavy pruning should be done right after the flowers have passed. Spring pruning should be done only to remove winter damage.
 
21. Deadheading the lilac will improve the shrubs ability to flower each year and keep it from producing seed. Most lilacs are cultivars, they can only be reproduced by cloning. Seed from a cultivar will almost always be a different shrub. 

22. Look for disease several times a year. lilac borer is rare, lilac leaf miner common. Kill lilac borer in the hole, seal any hole with garden wax or potters clay, evaluate each year as wound may heal. Leaf miner usually does minimal damage, but it can be easily recognized by its ink spot signature; remove that section of the leaf and destroy. Powdery Mildew is unsightly but rarely hurts the plant. Most other disease issues are addressed by good maintenance practices.

LILAC QUESTIONS:  jeffeyoung@yahoo.com