Lottah Nursery Tasmania, Australia

LILACS - FAQ

Frequently asked questions and answers about lilacs and their cultivation are listed on this page. More will be added when we know what the questions are.

Why aren't my lilacs flowering? (back to top)
Assuming that the climate is suitable and the plants are healthy and getting sufficient winter-chilling check the following:
a) the flowering buds have not been pruned away in winter
b) flower buds had not been frost damaged
c) plants are getting sufficient sunlight
d) nitrogen/potassium ratio is adjusted for flowering - reduce nitrogen if growth is excessive
e) pH is around 6.5
f) clone is not in juvenile stage making a lot of vegetative growth
g) clone is not floriferous - we have found some clones to have poor flowering, e.g. our S. x hyacinthiflora 'Clarke's Giant'.

Would deep planting of grafted lilacs establish scion roots? (back to top)
Our limited experience using constriction ties on nurse-grafts over a range of rootstocks suggest that while it is possible with juvenile material, the likelihood decreases with increasing age, i.e. more than a few months old. However any suckers emerging from the scion underground are likely to initiate their own roots.

Should grafted lilacs be planted with the graft underground? (back to top)
Probably; at worst that will hide the unsightly union. However any rootstock suckers developing will emerge from underground and be more difficult to remove completely.
The belief held in certain gardening circles that grafted lilacs do not flower unless they form their own roots is a fallacy. Some of our newly introduced Russian cultivars grafted in December 2004 were flowering 10 months later when plants were standing around 300 mm high.

Why are self rooted lilacs superior to grafted plants?(back to top)
a) no long term incompatibility
b) no rootstock suckering problem
c) generation of multiple stems for renewal pruning
d) easy multiplication with clonal suckers
e) no loss of plant if top is lost to blight or animals - more shoots will emerge from the root system
f) dwarf varieties require their own roots to preserve size

How long do I have to wait for the first flowers?(back to top)
Most varieties are precocious and flower the second season, if not the first, in the greenhouse; provided plants make normal growth, flowers may be expected the year after planting.

I live in (somewhere) - would lilacs grow here? (back to top)
Best advice is to check neighboring gardens for presence of lilacs. Given the popularity of the genus their absence would probably indicate their unsuitability. Presence of apple trees is likewise another good indicator that the area experiences sufficient winter chilling for growing lilacs. For marginally suitable areas with lower winter chilling we would suggest trying S. protolaciniata or its hybrids x chinensis. Please check our page on warm climate lilacs.

What fertilizers should I use for lilacs? (back to top)
Check soil acidity and add lime/dolomite in late Autumn or early Winter to bring pH up to around 6.5 - at the rate of no more than 250 g/m2. If phosphorous is required add some a few weeks after liming. Nitrogen and potassium are best applied in split applications through the growing season.
Alternatively add your favorite mix approximating 5-10-10 (relatively low nitrogen and high potassium to encourage flowering) a few weeks after growth begins. On no account should concentrated fertilizer other than the slow release types be applied into the planting holes as excess salts would damage emerging roots.
Another method used by growers elsewhere is to apply fertilizers in Autumn but we have no first-hand experience in this.
We link to an article for treating clay soils with gypsum.

How long do lilacs live? (back to top)
In the U.S. vulgaris selections growing at the Governor Wentworth estate in Portsmouth, N.H. are reported to be 250 years old. Trunk diameters approaching 600 mm are not unknown.
S. pekinensis trees in their natural habitat have been reported to have trunk diameters over 600 mm and standing at 12 m high, which would make them fairly ancient trees.

Would suckers emerging from self rooted lilacs cause a problem in later years? (back to top)
We suspect this is likely - a sharp spade to remove undesirable suckering in the early stages should prove temporary respite.

Can lilacs be multiplied using suckers? (back to top)
Certainly, if they are on their own roots and not grafted. Simply dig up the sucker with sufficient roots after leaf fall and transplant them to another site.
For a better root system girdle the sucker or use electrical cable ties for constriction underground to encourage more profuse rooting during the second season.

Do you export lilacs outside Australia? (back to top)
Generally we encourage northern hemisphere customers to purchase from north America or Europe because the seasons are synchronised. Tasmania has a relatively mild climate and plants do not get sufficient winter chilling until late August. This is rather late in the season to be planting lilacs in the north.
Although we have successfully exported lilacs to Japan, our preference is for dealing with southern hemisphere customers.

How do I learn more about lilacs? (back to top)
A great deal of information together with a good selection of images is available in Fiala's book, Lilacs: The Genus Syringa.
Beyond that, join the International Lilac Society to keep up with the latest in lilac happenings:

ILS Secretary
c/o The Holden Arboretum
9500 Sperry Road
Kirtland, OHIO 44094-5172
USA.

How do I prune lilacs? (back to top)
Go to our Pruning page.

How large are the plants offered for sale? (back to top)
There would be a fair amount of variation amongst the different cultivars. Dwarf varieties may be expected to be offered as smaller plants. Size of tissue cultured lilacs bear some relation to the time when they were deflasked as well as on cultivar charcteristics. In general we are more interested in providing an adequate foundation in the form of a good root system than in stem height.
To be more specific 'Maiden's Blush' offered in 2004 range from 500 mm to 1 m height, often with multiple stems.

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