Preparing and maintaining annuals: it’s not rocket science!

Annual flowers are a wonderful way to transform a balcony, patio or garden bed into a colourful space. Geraniums, impatiens, begonias and lobelias offer beautiful combinations throughout the growing season.

But how do you keep annual flowers healthy and blooming into fall? The key is a few simple habits: choose the right location, prepare a suitable potting mix, water according to actual conditions and avoid overfertilizing.

At Jardin Chez Michel, located at Montreal's Jean-Talon Market since 1968, we help gardeners select and care for their plants. Here is our practical guide to planting and caring for annual flowers in Quebec, informed by university horticultural research and extension recommendations.

1. Choose annual flowers for your sunlight conditions

Before buying plants, observe your growing space. How many hours of direct sunlight does it receive? Is it sunny in the morning or during the hottest part of the afternoon? These details can make a big difference.

Geraniums: for sunny locations

Balcony geraniums, generally belonging to the genus Pelargonium, appreciate bright conditions and several hours of direct sun. They are popular choices for patio containers and window boxes. During heat waves, monitor container moisture carefully.

New Guinea impatiens: for partial shade

New Guinea impatiens produce colourful flowers in bright locations, often performing well with morning sun and some protection from intense afternoon sunlight. Certain cultivars tolerate additional sunlight when moisture is adequate.

Rieger begonias: for gentler light

Rieger begonias generally prefer bright conditions without prolonged exposure to harsh direct sunlight. Proper watering and good air circulation help maintain healthy plants.

Deep Red geranium: a beautiful option for sunny balconies.

New Guinea impatiens: colourful blooms for bright, partly shaded locations.

Rieger begonia: beautiful flowers in generally gentler light conditions.

Wax begonias: versatile plants for beds and borders

Wax begonias, often sold as Begonia semperflorens, are known for their compact habit and abundant flowers. Depending on the cultivar and conditions, they can grow in partial shade or full sun. Afternoon shade may help in particularly hot locations.

They are excellent for edging, garden beds and group plantings. Bedding packs make it convenient to plant several flowers at once.

Wax begonias: a lovely choice for colourful borders and flower beds. Explore our packs of nine plants.

White lobelias: for borders and container arrangements

Lobelias, particularly Lobelia erinus, are valued for their delicate flowers and compact or trailing growth habits, depending on the variety. They work beautifully in window boxes, hanging baskets and garden borders.

They generally prefer consistently moist but well-drained soil. Flowering may slow during periods of intense summer heat. Light trimming after the first flush of flowers, combined with appropriate watering, may encourage renewed growth and blooming when conditions improve.

White lobelias: delicate flowers for borders, window boxes and mixed container arrangements.

Growing requirements vary by cultivar. Explore our annual flower collection for more options.

2. Prepare the right potting mix

Successful planting begins below the surface. Roots need water, nutrients and oxygen. Growing media that are too compact or constantly waterlogged can restrict healthy root growth.

The University of Maryland's guidance on container growing media explains why good aeration and drainage are essential.

For pots and planters: use a container potting mix

Choose a growing medium formulated for containers. It should retain adequate moisture while allowing excess water to drain. Ordinary garden soil used alone is usually too dense for small containers.

For garden beds: add compost when appropriate

Mature compost can improve certain physical and biological soil properties and contribute organic matter. However, not every garden bed requires large additions of compost.

Commercial potting mixes may already contain compost and fertilizer. There is no universal need to add one part compost to every two parts of potting mix.

Isabelle potting mix: an option to consider for container plantings.

Isabelle marine compost: an organic amendment to use according to soil needs and label directions.

3. When should annual flowers be planted in Montreal?

Most greenhouse-grown annual flowers are sensitive to frost. In the Montreal area, late May is often a useful reference point for outdoor planting, but actual weather conditions should always guide your decision.

Watch for cold nights, particularly with impatiens and begonias. If you purchase plants before outdoor temperatures are suitable, keep them sheltered or protect them when necessary.

Hardening off: an important step

Greenhouse-grown plants may need time to adjust to outdoor sunlight, wind and changing temperatures. Gradually increase their exposure over several days rather than placing them directly in full sun all day.

4. Plant annual flowers in five simple steps

1. Check drainage: clean reused containers and make sure excess water can escape.
2. Lightly moisten the potting mix: it should be damp, not waterlogged.
3. Gently remove the root ball: support the plant without pulling on its stem.
4. Follow proper depth and spacing: for most annuals, keep the top of the root ball level with the surrounding growing medium.
5. Water after planting: moisten the root zone to settle the potting mix around the roots.

When planting in garden beds, avoid working soil that is excessively wet, as this increases the risk of compaction.

5. Water wisely: observe instead of following a rigid schedule

There is no universal watering frequency. Water needs depend on container size, sunlight, wind, temperature and plant species.

In pots and planters

Check the moisture in the upper few centimetres of potting mix. When it has dried sufficiently for your plant's needs, water slowly until a little water drains from the bottom.

Avoid leaving containers standing in water-filled saucers for extended periods.

In garden beds

Water deeply enough to reach the root zone rather than repeatedly wetting only the surface. Watering near soil level, preferably in the morning, can also reduce the time foliage stays wet.

During heat waves, small containers in sunny locations may dry quickly. Check them more frequently, but do not water automatically without assessing moisture.

6. Fertilizing annual flowers: 20-20-20 or 15-30-15?

Container-grown annuals have a limited volume of growing medium. Nutrient levels can decline as plants grow and repeated watering causes leaching. Supplemental fertilizer may therefore be helpful.

The three numbers on a fertilizer label represent its guaranteed proportions of nitrogen (N), phosphate expressed as P₂O₅, and potash expressed as K₂O.

• Nitrogen: contributes to leaf and plant tissue development.
• Phosphorus: plays a role in energy metabolism and plant reproduction.
• Potassium: supports water regulation and several physiological functions.

Jardin Chez Michel 20-20-20: equal proportions of N, P₂O₅ and K₂O.

Jardin Chez Michel 15-30-15: a formulation with a higher relative phosphorus proportion.

Should you alternate between these fertilizers?

Not necessarily. Both 20-20-20 and 15-30-15 can be useful in appropriate situations, but a higher phosphorus concentration does not guarantee more flowers when the plant's phosphorus requirements are already satisfied.

University extension recommendations emphasize matching fertilization to the growing medium, plant needs and application rate. Excess fertilizer can lead to salt accumulation, root damage or unbalanced growth.

Always follow product label instructions. Browse our fertilizer collection for more options.

7. Maintain your plants for longer-lasting blooms

Removing faded flowers, known as deadheading, can encourage some annuals to produce additional blooms. It also helps maintain a tidy appearance.

However, deadheading is not essential for every variety. Many modern cultivars flower for extended periods without requiring the regular removal of spent blooms.

Remove damaged or diseased foliage, inspect your plants regularly and lightly prune overly leggy plants when appropriate for the species.

For lobelias, light trimming after the first flush of flowers may help encourage renewed growth, especially when temperatures become cooler.

8. Common annual flower care mistakes

• Planting too early: cold nights can damage tender annuals.
• Choosing the wrong exposure: partial-shade plants may struggle in intense sunlight.
• Using compacted potting mix: roots need oxygen to remain healthy.
• Following a rigid watering schedule: water requirements change with the weather.
• Overfertilizing: more fertilizer does not necessarily mean more flowers.
• Overcrowding planters: plants compete for water, light and nutrients.

9. A simple maintenance routine through fall

• Regularly: check container moisture, especially during hot weather.
• Weekly: inspect foliage and remove dead or diseased growth.
• As needed: fertilize, lightly prune and remove spent flowers.
• Late in the season: monitor cold nights and protect containers when possible.

With suitable potting mix, the right growing location and regular maintenance, annual flowers can brighten your space for months. And it really does not have to be complicated!

Horticultural and scientific references

1. University of Maryland Extension — Growing Media (Potting Soil) for Containers. Root aeration, potting media and drainage.
2. NC State Extension — Plants Grown in Containers. Irrigation and nutrient management.
3. Iowa State University Extension — Care of Plants Growing in Containers. Fertilization and maintenance.
4. University of Illinois Extension — Lobelia. Exposure, heat sensitivity and pruning.
5. University of Missouri Extension — Flowering Annuals: Characteristics and Culture. Species selection and growing conditions.
6. Purdue University Extension — Growing Annual Flowers. Planting and deadheading.