Scientifically known as "Matthiola Incana", Stocks are annual or biennial plants that belong to the Brassicaceae family. They are known for their heavenly spicy fragrance and vibrant colours, are a favourite among many florists, however they can be a bit tricky to grow. I tried for years and they were just never quite as tall, or fluffy or scented or amazing as the ones I could pick up at the wholesaler.
So honestly I thought that I needed some special skills to growing scented stocks or a greenhouse set up. Turns out I was just too impatient and looking for too much perfection, and they can be successfully grown outside here in the UK and look stunning.
CHOOSING THE RIGHT VARIETY
There are several varieties of scented Stocks to choose from. Some popular ones include:
Matthiola incana 'Cinderella Series' - This series is popular for its compact growth habit and is ideal for containers and small garden spaces. The breeding focus of this series is to produce smaller, more manageable plants. Therefore of you want long stems this is not the variety you need to grow.
Matthiola incana 'Iron'- Bred in Japan this variety is developed with an emphasis on strong stems and uniform growth, making them particularly suitable for use as cut flowers. The breeding focuses on producing robust plants that can withstand various conditions while providing an abundance of fragrant blooms.
Matthiola incana 'Katz' - The 'Katz' series of stocks is also Japanese-bred. These varieties are known for their long stems and profusion of fragrant blooms, making them ideal for both garden displays and cut flower arrangements. The 'Katz' series was developed to provide a wide range of colours and a strong fragrance, ensuring that they are a popular choice among gardeners and florists alike. Their breeding emphasizes uniformity and vigour, resulting in plants that are both aesthetically pleasing and resilient.
DOUBLE BLOOMS
Only around 50% of stock plants grow as doubles (plants with double blooms) is due to the genetic inheritance of the double-flower trait in stocks.
The double-flower trait in stocks is controlled by a recessive gene. This means that for a stock plant to produce double blooms, it must inherit two copies of the recessive gene (one from each parent). Plants that inherit only one copy of the gene will have single blooms but can still carry the gene and pass it on to their offspring. This is referred to at Mendalian Genetics.
In a typical Mendelian inheritance pattern:
If both parent plants are carriers of the double-flower gene (heterozygous), their offspring will display the following ratios:
25% will be double-flowered (homozygous recessive).
50% will be single-flowered but carriers of the gene (heterozygous).
25% will be single-flowered and not carriers of the gene (homozygous dominant).
However, horticultural practices often involve selecting and breeding stock plants to increase the likelihood of double blooms. Breeders typically select parents that are more likely to produce a higher percentage of double-flowered offspring.
For gardeners, this means that when planting stock seeds, only about half of the plants will grow as doubles unless specific breeding techniques have been employed to increase this percentage. Some seed suppliers offer "double-flowered" seed lines that have been selectively bred to maximize the occurrence of double blooms, but even in these cases, achieving a 100% double-flowered crop is challenging.
So if you want to only grow the double blooms then it is essential to weed out the singles at an early stage.
PREPARING THE SOIL
Scented stocks thrive in well-draining soil with a pH level between 6.0 and 7.5. To ensure that the bed these are planted in is well prepared:
Loosen the Soil - Use a garden fork to loosen the top 12-15 inches of soil.
Add Compost - Mix in 2-3 inches of compost to improve soil fertility and drainage.
Test the Soil - Conduct a soil test to check the pH level. If necessary, add lime to raise the pH or sulfur to lower it.
SOWING SEEDS & SELECTION OF DOUBLES
Sow 3-4 seeds into a plug tray filled moist compost and cover with a sprinkle of compost or vermiculite and place into a propagator to maintain even mosture, do not allow to dry out before seedinling germinate. Ideal temp 18-20ºC.
After germination grow on at a day temperature of around 16ºC and a night temperature of around 13ºC.
 After 8 days remove the last to germinate seedling with a tweezers. If only two seedlings germinate keep both.
 Around day 9-10 allow the soil to dry slightly which will make the final selection easier.
Around day 14 before the first true leaves emerge final selection can take place for doubles : The double-flowered seedlings are more vigorous and grow more rapidly. Double-flowered seedlings have larger and longer cotyledons with a more irregular/elliptical shape and are a lighter green colour. Single-flowered seedlings will be shorter, with smaller cotyledons, more round/oval shape and will be darker green colour - these can all be removed at this stage
When the seedlings have 4-5 true leaves, transplant out to final flowering positions. It seems too early, yes they look very small but getting then into the ground is key becaise they need space to develop a long root system. They can be planted very close together - around 10-15cm
Once planted ensure that you install netting of a framework of canes to support the plants as once the flower buds form they get very top heavy and flop over. Net when the plants are about 30 cm tall. Add additional netting as the plants continue growing tying in if necessary.
The highest day temperature along with the photoperiod are the mechanisms that affect flower bud initiation. Optimum temperatures for flower bud initiation are around 20ºC for Early Iron series, around 18ºC for Iron series and around 15ºC for Katz but can vary depending on day length. Flower bud initiation is also dependant on when the plants have more than 10 true leaves. Following initiation, warmer temperatures and longer days accelerate development whereas cooler temperatures and shorter days lengthen crop time.
This can all get a bit challenging and our weather here in the UK is really not reliable. If you are serious about stocks and want to be a specialist grower then having temperature controlled greenhouses would be a must but for the average flower farmer that's just not possible.
Consistency is key and avoiding heat stress, above 21°C will negatively impact flower bud development and may result in poor-quality blooms or reduced flowering. So these are COOL flowers and in the UK it rarely gets much above 21°C so our conditions here are ideal.
If starting seeds indoors, ensure a gradual transition to outdoor conditions to avoid temperature shock. Hardening off seedlings by gradually exposing them to outdoor temperatures helps them acclimatise.
WATERING
Keep the soil consistently moist, especially during dry periods. Avoid overwatering, as this can lead to root rot.
FERTILIZING
Feed the plants with a balanced fertilizer every 4-6 weeks during the growing season. An organic option, such as fish emulsion, or liquid seaweed works well. Stock has a higher need for potassium so target the N:K ratio at 1: 1.5. Avoid high rates of ammonium as it promotes softer growth and thinner stems.
MULCHING
Applying a 2-inch layer of mulch around the plants will help to retain moisture and suppress weeds.
PESTS & DISEASES
Watch for aphids, caterpillars, and whiteflies. Matthiola can also be susceptible to downy mildew and rust. If you have a problem with this then ensure good air circulation by spacing plants further apart and avoid overhead watering.
HARVESTING
Stocks will flower in 13-25 weeks from sowing based on when the plants initiate flowers.
They are a one hit wonder and once cut the ground can be cleared and used for another crop. Cut stems with 7-15 open flowers on the spike.
For the best fragrance, cut the flowers in the morning when the scent is most potent. Place in water immediately to keep them fresh.
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