Frequently asked questions about lilac

Its incomparable fragrance is associated with the long-awaited arrival of spring. Purple, pink, white or bluish, its clustered inflorescences attract all pollinating insects. Easy to grow, the lilac is one of the must-have shrubs in a garden!

To which botanical family does the Lilac belong?

The lilac belongs to the genus Syringa which has about twenty species and is part of the Oleaceae family.

Syringa vulgaris is native to the Orient as is Syringa persica, the Persian lilac, a lesser known but equally fragrant species. The lilac is a deciduous shrub that can reach 1.5 to 7 meters in height depending on the species and varieties.

How to water the lilac?

Once well established in the ground (more than 3 years old), lilacs can withstand a few dry spells, especially when it comes to the Syringa vulgaris type, as the cultivars are more sensitive to water shortages.

In the years following planting, the soil must remain cool throughout the summer. Mulch it copiously to preserve its humidity. Beware of winter drought in southern regions on recently planted plants!

In pots, the substrate should never dry out completely during the summer season, but should not remain soggy. In winter, reduce watering to the strict minimum.

How to grow lilac in the ground?

Lilac is not a difficult shrub to grow as long as the soil is well drained. Stony and chalky soils do not discourage it, on the contrary! It appreciates a very sunny exposure but can tolerate half-shade in southern regions.

The typical species Syringa vulgaris tolerates drought much better than its cultivars, which need always fresh soil, especially in the heart of summer. A thick mulching of the foot will help to maintain it.

How to propagate lilac?

The easiest way to propagate suckering species is to take the shoots in autumn, by detaching them from the mother plant with a spade and a pair of secateurs. You can then replant them in another part of the garden immediately and water them regularly if it does not rain enough to ensure that they take root.

Cutting is easy to do. Heel cuttings or T-cuttings are the most suitable techniques for lilacs. This type of cutting is done in summer.

Take an end of a semi-lignified secondary stem carried by a healthy branch of which you will keep a small part (bark for the heel cutting, section of two centimeters for the cutting in 'T'.

Place the cutting in a bucket containing a mixture of potting soil or sand, or even a commercial 'Special seedlings and cuttings' substrate after having left only the two leaves at the top. Water and place the cutting in the shade in a place sheltered from the wind.

As soon as the first signs of recovery appear, repot in a larger pot and in a richer substrate. Keep it until the fall of the following year, when it will be time to plant your lilac in the garden!

How to plant lilac in a pot?

Potting lilacs is best done after they have bloomed in late spring.

• Choose a container or a pot of at least 40 cm in all directions with a hole in the bottom.
• Provide a layer of draining material at the bottom of the pot (pozzolan, gravel, clay balls, etc.) to ensure good drainage, as the lilac hates having its roots constantly soggy.
• Make up a mixture of potting soil, garden soil (if it is calcareous, it is even better), river sand and compost to install your shrub.
• Leave the neck of the plant 3 cm below the top of the pot.
• Pack well around the base of the plant.
• Water and adjust the height of the substrate if necessary.

How to plant a lilac in the ground?

Choose a sunny spot to plant your lilac.

• Moisten the root ball in a basin of water at room temperature after removing it from its container.
• Dig a hole twice the size of the root ball in all directions.
• Add well-decomposed compost and organic fertilizer pellets to the soil, and add a little fireplace ash if you have it. If the soil is very clayey, mix in a few shovelfuls of river sand.
• Pour this mixture into the bottom of the hole and adjust the height of the soil so that the neck of the plant is just below the soil surface.
• Backfill, keeping the shrub upright.
• Pack well around the base.
• Water copiously.
• Form a basin to retain water at the foot of the lilac.

How to prune a lilac?

Future flowering will take place on the previous year's shoots, so pruning should be done just after the spring flowering and in a delicate manner!

In addition to the pruning of wilted flowers (Cf. 'Should we cut the wilted flowers of the lilac?'), a pruning of the aerial parts can be considered but only on the subjects already well established (3 or 4 years).

The purpose of this pruning will be to clear the center of the shrub by cutting off dead or crossing branches in order to let in light and to favor natural ventilation.

If an old lilac becomes less floriferous and bald at the base, it will be possible to perform a drastic pruning of all the aerial parts. Cut the dead and oldest branches short. Cut back the others to 30 cm from the ground. This pruning should only be done in winter during the resting period, well before bud break (opening of the buds). Obviously, flowering will be compromised in the spring, but the old lilac will find a new youth.

Some species and varieties have a tendency to spread by suckers. You can prune them as close as possible to the mother plant, but be aware that this type of pruning stimulates the appearance of suckers.

Do I have to cut off the wilted flowers of the lilac?

This is not a requirement on non-remontant varieties, but it is possible to cut off spent inflorescences for aesthetic reasons. Prune above the first large bud just below the flowering stem. Cut at a sharp bevel away from the bud so that water does not linger on it.

Prune remontant varieties (which rebloom in autumn) systematically after flowering by simply cutting off the stalk of the cluster, this will stimulate the second flowering, as the shrub will not spend its energy on producing seeds.

Is it possible to grow a lilac in a pot?

It is quite possible to grow a lilac in a pot, so choose a low-growing variety such as Syringa meyeri 'Palibin' with pink flowers, S. julianae 'Red Pixie' with purple flowers, 'Bloomerang Pink' a hybrid with remontant pink flowers, or for those who like bluish shades Syringa persica 'Laciniata'.

In pots, it is important to be particularly careful about watering, as the substrate should never dry out more than 3 cm on the surface. Be also careful with a too hot exposure in the southern regions, prefer to place the pot in a shady area during the hottest hours of the day in summer.

Remember to feed the lilac with a liquid organic fertilizer (following the manufacturer's advice) or a mixture of ground horn and dried blood every 3 months from March to September.

Is the Indian lilac in the same genus as the common lilac?

No, the Indian lilac (Lagerstroemia indica) is part of the genus Lagerstroemia and of the Lythraceae family. As its Latin name does not indicate, it is native to China and not to India as one might think.

It is a tree which can reach 3 meters in height for as much of spread. It blooms in summer and is not hardy unlike the classic lilac.

Is the lilac hardy?

Yes, all species of lilac are hardy up to -15°C or more in well-drained soil, so it can be introduced in most gardens.

Attention: the Indian lilac (Lagerstroemia) which is not part of the genus Syringa (Cf. 'Is the Indian lilac part of the same genus as the common lilac? ') is not hardy, it will only be planted in the mildest regions.

When is the best time to plant lilac?

The beginning of autumn is the best time to plant the lilac, however winter and early spring are also other opportunities for planting.

Be careful, if you plant lilac in the spring, to wait until the end of the flowering period and be particularly vigilant about watering throughout the summer.

What are the most interesting species and varieties of lilac?

Among the numerous species and cultivars, here is a small selection which is not exhaustive:

• Syringa Vulgaris otherwise known as 'French lilac' or 'common lilac' comes in multiple cultivars selected for the color of their flowers. The typical species bears panicles of lilac colored flowers very perfumed.
• Among the cultivars, 'Souvenir de Louis Spaeth', 'Prince Wolkonsky' and 'Charles Joly' present clusters of purple flowers, 'Captain Baltet', 'Double bleu' and 'Firmament' decline beautiful shades of blue, 'Belle de Nancy', 'Belle de Moscou' or 'Katerine Havemeyer' resplendent in pink, while 'Madame Lemoine' remains the undisputed star of the white lilacs.
• Syringa patula 'Miss Kim' is a graceful and small (1.5 m in all directions) cultivar, ideal for small gardens. The clusters of flowers are full of small, deliciously scented pale pink flowers that maintain a very airy feel.
• Syringa meyeri 'Flowerfesta White' forms a bush of 1,25 m in all directions. It is ideal in pots or in city gardens. The fragrant, white spring flowers are repeat flowering in September/October. Note that this recent obtention is available in blue and pink.
• Syringa microphylla is an interesting species for its compact bushy habit (2 m in all directions) and its long-lasting (April to June), sometimes remontant, flowering from September to the end of October. Superba' is particularly easy to grow and is covered with pink flowers.

What are the most common diseases of lilac?

Very vigorous, lilacs are only really affected by fire blight, which manifests itself as black stained leaves and blackened shoots. Cut off all affected parts down to the sound wood, water with a decoction of garlic and spray with horsetail manure.

What are the main pests of lilac?

Otiorhynchus, cantharides and lilac moth (a caterpillar) are the most common pests. Spray fern purin every 15 days to prevent them.

Successfully planting a shrub

There are shrubs for every use in the garden. In a grove, isolated, in a bed or in a hedge, these plants will accompany you for many years if you take a few precautions when planting them.

Before buying

It is necessary to find out beforehand about the shrubs you wish to introduce into your garden. Each terroir, climatic zone or type of soil will have a certain number of plants.

Thus, turn to acidophilic shrubs such as rhododendron, camellia or hydrangea if the pH of your soil is below 6. In neutral soil, everything is allowed by adding the right amendments if necessary (compost, sand, green manure...). In soil with a pH higher than 7, choose plants that appreciate limestone! You will find pH tests in all garden centers.

Remember also to make your choice according to the exposure of your garden, some shrubs appreciate the shade, others really need full sun to thrive.

Another important parameter is the persistence of the foliage, especially when it comes to creating a privacy hedge! Think about this before choosing your shrubs!

If you prefer flowers, think about encouraging biodiversity by choosing shrubs that will bloom over several months and produce berries to feed birds and small mammals.

Finally, find out how tall your shrub will be so you can tailor your purchase to the size of your garden. There are low-growing varieties that are ideal for urban backyards, patios, or very small gardens!

Soil preparation

Logically you have made your choice according to the parameters described above. We will therefore start with a shrub adapted to the soil in which it is to be planted, which avoids many worries.

• Ideally, the hole should be dug at least two weeks before planting, which will give the soil time to loosen and rebalance itself, thus promoting a better recovery.
• Choose the best planting time, depending on whether it is a bare root or container shrub. As a reminder, bare-root shrubs are planted in fall and winter outside the frost period, while containerized shrubs are planted in fall or spring. Note that the first ones have a better chance of recovery.
• Soak the root ball in room temperature water for at least an hour to hydrate it. Dress (prune) the roots of bare root shrubs if necessary and prune them.
• At the bottom of the hole, spread a thick layer of a mixture of garden soil and compost, add a good dose of mycorrhizae to promote recovery and ensure a better resistance of your shrub to weather conditions, pests and diseases. Don't neglect this step because the results are often spectacular!

Planting

• Install your shrub in the hole previously prepared by adjusting the height so that its collar is flush with the ground. Add soil to the bottom of the hole if necessary.
• Fill in the empty spaces until the hole is completely full.
• Water thoroughly to evacuate any air bubbles in the soil, then add more soil if the level has dropped during watering.
• Create a basin at the foot of your shrub to facilitate watering and to keep water at the foot of the plant.
• A mulch will prevent competition from weeds and protect the stump from the cold in winter and from evaporation in summer. This mulch is very useful on shallow-rooted shrubs such as raspberry bushes for example. Avoid it, however, on xerophilous shrubs that would not tolerate this constant humidity! To prevent weeds from growing, use a mineral mulch for these plants, which will retain heat and release it while remaining very attractive.

After planting

Every shrub needs about three years to establish itself and develop its root system properly. Be very careful about watering spring plantings, which will require a lot of water in the summer to ensure their recovery. This is why fall plantings are preferred, however, they can only be done on hardy varieties.

Remember to water your shrub well the three years following its planting, and don't forget to do so in winter, especially in southern regions where drought can last for long weeks even in winter! If it rains enough, don't add more water, because an excess of water can be as harmful as a lack, it's all a question of the right dosage.

Scratch a little compost and a few granules of organic fertilizer at the foot of the shrub in the spring to support the vegetative recovery, do the same after a pruning operation.

Pruning will take place at different times depending on the variety and the flowering period if the shrubs are in bloom.

A cleaning pruning in winter will favor the entry of air and light in the center of the shrub, which will avoid the installation of many parasites and diseases. Pruning also ensures a more opulent flowering on the shrubs that bloom on the new shoots produced.

With all these precautions, from selection to planting to maintenance, you are assured of a much better success with your shrubs!

Knowing where to plant your shrubs

Each garden has its own ecosystem, divided into several zones that may or may not be of interest for planting shrubs. It is important to know where to plant them to ensure optimal success.

The microclimates of the garden

Each garden has its own specificities. Exposure, climate and soil type will help you determine the ideal location to plant your shrubs.

1- Exposure

With a southern exposure, the garden will be able to accommodate most flowering shrubs or variegated foliage because, contrary to what one might imagine, this exposure is not the most delicate, except in very hot and dry regions where the choice of plants should be made accordingly. An eastern exposure poses a little more concern, because the morning sun after a frost can cause the plants' tissues to burst. The prevailing winds also often come from the East, drying out the plants, breaking branches and inducing more evaporation. A western exposure will avoid the phenomenon of burning after the frost, the shrubs will be subjected to the afternoon sun and will have less direct contact with the wind. In the North, the cold and humidity are more important, so hardy shrubs should be planted there, which can tolerate little sunlight.

2- Climate

Each region, or even micro-region, has its own climate, well beyond the specificities between the North and the South. However, in the North and in mountainous regions, it is wise to plant shrubs adapted to cold and humidity. Avoid non-hardy subjects, of Mediterranean or tropical origin, which would have a hard time establishing themselves.

Rainfall is another important factor. Some regions are subject to regular and very frequent rainfall. Shrubs should be chosen with this in mind. As for snow, it can be a good winter protection against the cold, but in regions where it is abundant, you should preferably choose hardy shrubs with branches that are flexible or strong enough not to break under its weight.

In very hot regions where the summer is very dry and the winter mild, you can introduce more chilly subjects that appreciate this type of conditions and are resistant to drought in order to avoid continuous watering.

Regions subject to thick and frequent fog but where the temperature is mild will appeal to many shrubs because the dew that settles down facilitates gas exchanges and of course increases the hygrometry rate. On the other hand, the most fragile ones are likely to be sensitive to cryptogamic diseases.

3- The nature of the soil

Acid, fertile limestone, poor or balanced, the soil of your land will partly determine the choice of your shrubs. There is no point in trying to grow calcifugic plants that require fresh soil, such as rhododendrons or camellias in the garrigue of Marseille! You will be faced with disappointment. Always choose your shrubs according to their specific needs.

A hydrangea with blue flowers

You chose it for its beautiful deep blue color, but surprise, once installed in your garden for some time, your blue hydrangea has turned into pink. Did the fairies of 'Sleeping Beauty' come to you? No way! Let's see how to give it back its original colors.

Mysteries of Nature

Hydrangea macrophylla, better known as the florist's hydrangea, is a spectacular flowering plant, as much for the rounded size of its inflorescences as for its colors. Some varieties have a variable flower color passing strangely from blue to pink. There is no mystery behind this, it is simply a physical phenomenon that comes into play in the color of the flowers: the pH and the composition of the soil.

In a soil with an acidic tendency, the flowers remain blue or are purple if the variety chosen was it at the base.

In a calcareous soil with a pH higher than 7, the color turns spontaneously to pink, or even to red if the variety allows it.

Another parameter concerning the soil, the iron and aluminum content in their assimilable forms must be sufficient. Knowing that in calcareous soil, iron is very poorly assimilated by plants, everything is explained...

How to maintain the blue color in hydrangeas?

As we have seen, the color varies according to the pH of the soil. It is therefore obvious that it will be a little complicated to maintain a beautiful blue color in calcareous soil. However, here are a few ways to help:

• Apply a fertilizer rich in potash and alum in August when the future flower buds are forming to prepare for the next year's bloom.
• Apply every spring and during the growing season a bluing product.
• Be careful with tap water, which, if hard (calcareous) will not suit your hydrangea. Always prefer to water it with rainwater in these conditions.
• When planting, if the soil is chalky, dig a pit of 1 meter by 1 meter and fill it with heather soil, compost and a little dried blood before installing your hydrangea. Each fall, scratch some heather soil on the ground.
• If the soil is very calcareous, prefer planting in a large container in a mixture of heather soil.
• Mulch the base of your hydrangea with a thick mulch of pine bark. This mulch tends to slightly acidify the soil. If you are a fan of mineral mulch, don't hesitate to mulch the base with crushed slate, known to give a beautiful blue color to the hydrangea.
• You can find it in DIY stores or garden centers under the name 'Blueing Fertilizer for Hydrangeas' . These products contain iron sulfate and alumina, in addition to NPK formulations adapted to hydrangeas.
• Remember to water your hydrangeas regularly so that they do not suffer from water shock and so that the roots can synthesize the elements provided.

How to choose your bamboo?

To appreciate the quality of a healthy and vigorous bamboo, you should not only look at its aerial parts but also unpack it to discover its rhizomes.

If it is impossible to remove the pot, i.e. if it is swollen by the rhizomes or bursts under their push, this is the plant you need.

Once the pot is removed, we observe:

• Root system condition with the presence of rhizomes. It is the future of your plant which will give the future turions. Check that the roots and rhizomes are dense enough.
• A beautiful hair (assimilating roots) with beautiful root caps mainly in spring when there is a resumption of the vegetation. These rootlets will allow a good absorption of water and mineral salts. They can go down to several meters under ground.
• The bamboo can develop a bun, that is to say to make a spiralization of the roots. What is a handicap for many plants is not for bamboos. Once planted, it will not repeat this way of growing. It has developed a bun by constraint due to the pot. Once released, the rhizomes will resume their horizontal growth.
• Advice: at plantation, separate the rhizomes which spiral by distributing them in the ground.
• In summary, it is better to choose a bamboo with few culms but many rhizomes than the opposite. Vigorous rhizomes are more important than beautiful stems. The future of your bamboo depends on the reserves stored in its rhizomes.

The characteristics of a rhizome

• Horizontal underground stem
• Hollow and partitioned stem (fistulous rhizome)
• The nodes carry eyes that will develop into new culms.
• Roots adapted to the storage of energy reserves (starch) for its future growth. A well-fed and well-maintained bamboo the year before will give beautiful culms the following year.
• It fixes the plant to the ground with its adventitious roots. There are also docking roots that make the culms more resistant to wind.
• The rhizome is a potential propagule. From a section of rhizome one can obtain another plant (cloning)
• Although endowed with a positive geotropism, the tip of the rhizomes sometimes emerges from the ground to give a culm (positive phototropism). It can also be diverted from its trajectory (stone...), go out of the ground and then enter it again under the effect of its positive geotropism.

The questions that we must ask ourselves are the following

Different types of underground devices ?

A cespitose bamboo has pachymorphic rhizomes (from the Greek prefix meaning thick) .

The apical bud of the rhizome evolves in thatch. It doesn't go very far in the ground. In this case, the internodes are short and more or less swollen. Horizontal growth is done only on a few centimeters. Bamboos with these pachymorphic rhizomes form tight clumps. They do not spread on the surface.

A tracing bamboo has leptomorphic rhizomes (from the Greek, leptos=thin and morphos=shape), often with unlimited growth (monopodial). In this case, the internodes are long and thin. Their growth is horizontal.

Does the plant have a good root system?

The most important is in the substrate which is not in sight. It is the rhizomes that will ensure the future of your bamboo plant and not its culms.

Was the bamboo well fed last year?

Its rhizomes, which store reserves thanks to the photosynthesis of its foliage, not only allow the plant to be fixed to the ground but are also the carriers of future culms. The good work of the nurseryman is mainly found in the quality and the richness of the rhizomes. The good conditions of culture (heat in spring for a good exit of the shoots and in summer to facilitate the accumulation of the reserves in the rhizomes) make it possible to obtain a subject with well augusted shoots, resistant to the cold and rich rhizomes for the future of the plant.

Bamboos for all tastes

Bamboo has become an essential plant in our gardens. Fast growing, sometimes even invasive, this carefree plant comes in countless varieties, each with its own place in the garden. Giant, slender or bushy, dwarf or variegated, you will find the bamboo that suits you!

Ground Cover

Take advantage of the power of expansion of this plant to cover spaces where you want to eradicate weeds or create green areas without worrying about requiring only low maintenance. Indeed, the tracing roots and the density of the foliage will prevent the regrowth of weeds and will avoid you the always painful chore of weeding.

Choose the Sasa genus with its shiny and wide foliage which will do wonders in shady and humid areas. In dry and sunny soils, Pleioblastus is preferable as it can be pruned at will and will cover large areas very quickly.

Isolated subject

Always very elegant installed in a large pot, it will enhance a wooden terrace. Cultivated in a pot, the water and fertilizer must be constant to keep the brightness and beauty of the foliage and avoid its wilting. For this use Semiarundinaria fastuosa will give good results because it is not very tracing. Its culms rise very straight like candles erected towards the sky. In the sun it takes a beautiful amber color very characteristic. Very graceful, Phyllostachys decora resists well to dryness and will find its place on Mediterranean terraces.

Boundaries and borders

Bamboo, if well contained, can also be used to create borders, as well as to stabilize sloping ground. The genera Sasa, Shibataea or Pleioblastus lend themselves well to the creation of borders and the delimitation of paths as long as they are well contained with the help of anti-rhizome barriers. In early spring, prune them very short to induce the formation of new foliage and keep a compact habit.

Bamboo hedges

This is the most common use of bamboo. These hedges offer excellent visual, acoustic and wind protection, creating favorable microclimates for fragile plants.

Fargesias and Phyllostachys are most often used to create hedges. Beware, because if the conditions are right for them, their growth can be very fast, and they will easily reach 15 meters high. But don't panic, they can be pruned in height as well as in width!