How to grow Petunia
One of the most popular summer bedding plants for hanging baskets, window boxes, and pots, this member of the tomato family is grown for its prolific and exceptionally long flowering period. The blooms are usually trumpet-shaped and are available in an enormous range of colours, forms, and sizes. Petunias can be either bushy and upright or long and trailing.
Petunias are fast-growing and can be expected to reach full size by late spring.
Zantedeschia is a genus of flowering plants from the family Araceae and is native to southern Africa. With a rich history dating back to the Ancient Romans, these deciduous or semi-evergreen perennials have been used as a symbol of celebration. Zantedeschia was Named after Professor Giovanni Zantedeschia, an Italian botanist.
There are two main forms of Zantedeschia: hardy and tender. Hardy forms of the plant can be grown outdoors, enjoy moist soil and full sun or partially shaded conditions - these are known as Arum lilies. Tender forms of Zantedeschia prefer being grown in containers or pots and should be brought inside over the winter - these are known as Calla lilies.
With tuberous flora in all colours from whites, yellows and oranges to deep reds and purples, Zantedeschias are not to be overlooked in any garden, as long as they have sufficient sunlight to grow in.
Ready to learn more about growing Zantedeschia? Read on for all there is to know...
Key Information
Soil pH
Position
Hardiness
Horticultural Divisions-
Habit | |
Bushy | Trailing |
‘Bee’s Knees’ | Amore series |
‘Black Velvet’ | Cascadia series |
Constellation series | Tumbelina series |
Fun House series | Fanfare series |
Go!Tunia series | Fortado series |
Espresso series | Itsy series |
Saguna Patio series | Designer series |
‘Mystical Midnight Gold’ | Pegasus series |
‘Phantom’ | ‘Sweet Miss Marvellous’ |
‘Pinstripe’ |
|
Where & when to plant Petunia
Position - Full sun or partial shade with shelter from strong winds
Soil - Fertile, moist, well-draining. Can be acid, alkaline, or neutral.
Flowering Period - Usually from around June to the first frosts, though some varieties (e.g., the Fun House series) flower earlier, from March until late summer.
Hardiness - H2/ tender. Unable to tolerate temperatures dipping below 1°C.
Plant your petunias outside once all risk of frost has passed in your area. This can vary depending on the region, though is usually around mid to late May. If your young plants arrive before it is safe to plant them out, pot into 9cm containers using a well-draining compost mix and keep in a frost-free environment such as a greenhouse, conservatory, or sunny windowsill. Alternatively, if space allows, get off to a head start by potting straight into hanging baskets, window boxes, or permanent containers and storing as above. Keep regularly watered but not soggy.
When the time comes, move your petunias outside into a sheltered spot (remember, their flowers can be damaged by strong winds). Any light level is fine apart from full shade. As well as containers, petunias can be grown in beds and borders as annual bedding. Use bushy varieties to line a path edge or fill gaps in the front of a border, and trailing varieties to cascade over the edge of walls and raised beds.
How to plant Petunia
- For planting in containers, first choose an appropriately sized pot. You may wish to grow your petunias on their own in a pot, or as part of a larger, mixed container display. Either way, ensure there are plenty of drainage holes in the bottom.
- If you are using a large or heavy pot, it can be a good idea to fill and plant it in situ to save yourself the trouble of moving once full.
- Use a good quality potting compost with some horticultural grit mixed in and, if not already present (check the labelling on the bag) some slow-release fertiliser granules.
- Start by partially filling the pot with compost; enough so that when placed on it the upper surface of the root balls are about 3cm lower than the top of the pot. In terms of spacing, petunias can be massed together quite for a dense and impressive display – think 6-7cm between plants. A general guide is three petunias in an average 22cm hanging basket, or five in a larger 30cm version.
- Fill around the plants with compost, firming down with your fingers then adding a little more so they are held tight.
- Pick up the container and lightly tap on the potting bench or ground a few times to help further settle the compost around the plant.
- Soak well with water.
- A mulch with horticultural grit will look attractive and help to prevent a ‘cap’ or crust forming on the top of the compost (something container plants can suffer due to the artificial nature of their watering).
- For planting in the garden, dig the soil area removing any large stones and weeds and breaking up any lumps. Mix in some organic matter such as manure or garden compost. If your soil is on the heavy side, now is also the time to add a generous helping of horticultural grit. Rake level and firm with your heels. Rake level again.
- Water plants well and allow to drain before planting.
- A good tip is to dig a hole twice the size of the root-ball. Fill with water and allow to drain before placing in the plant.
- Place the plant in the hole, ensuring the top of the root ball sits level with the surface of the soil. Too low and the plant may rot, too high and the roots can dry out.
- Give petunias a little more space in the open ground than you would in a container, aiming for around 30cm between plants.
- Backfill with soil and firm in gently with your foot.
- Soak well with water.
Mulch around the base with well-rotted organic matter.
What to plant with Petunia
For a professional-looking summer flowering container display overflowing with colour and texture, mix your petunia with other tender bedding plants such as pelargonium, nemesia, bidens, thunbergia, and verbena. For that all important foliage element, think helichrysum, artemisia, or dichondra.
How to care for Petunia
Pruning and Deadheading
Deadheading your petunias regularly throughout the flowering period will keep them looking neat and encourage further blooming.
Petunias are usually treated as annuals, meaning once they have finished flowering, they are simply removed to the compost heap and replaced with summer bedding. A light trim midseason may be required if they are starting to look untidy.
Watering
Petunias grown in containers require regular watering as they can dry out very quickly, particularly in warm weather. To avoid overwatering, a good rule of thumb is to allow the top couple of centimetres to dry out between soakings. To check this, wiggle your finger down into the soil/ compost until you feel moisture.
Petunia in the ground should be watered regularly for the first few weeks, and then in hot, dry weather.
Feeding
To get the most out of hungry summer bedding plants such as petunias, regular feeding is a must – particularly for those grown in a container.
In a container, petunias should be potted in a good quality compost with slow-release fertiliser granules mixed in, then fed with a high potassium liquid feed, such as tomato feed, at weekly intervals throughout the growing season to boost flowering.
In the open ground, mulch newly planted petunias with well-rotted organic matter, i.e., a layer of manure or garden compost applied to the soil around the plant. As well as boosting the nutrient content of the soil, this has the added benefit of suppressing weeds and locking in moisture.
After this, a weekly or fortnightly application of high potassium liquid feed, such as tomato feed, will boost performance significantly.
Cold Protection
Petunias originate from the warm climes of South America and will not survive a frost. Keep in a protected, frost-free environment until it is safe to plant them out, then remove to the compost heap at the end of the growing season.
Pests and Diseases
Overall, petunias are mostly trouble-free, though slugs and snails can be a nuisance, when plants are young. Encouraging natural predators into your garden, such as birds, frogs, toads, and hedgehogs, will make a big difference. Torchlight searches after dark (when slugs and snails are at their most active) are also effective, allowing you to collect the offending molluscs in a bucket and dispose of as you see fit. Relocating to a nearby woods or bagging up and putting in your freezer before popping them in the bin are said to be the most humane approaches.
Aphids can also crop up from time to time. Again, our advice is that these are part of a balanced garden ecosystem and the best approach is to leave them to their natural predators (e.g. birds, ladybirds, and wasps). When numbers are so large, however, that their feeding starts to inhibit and disfigure growth, you may feel it necessary to take action. Regularly blasting off with a hose or wiping away with a cloth or piece of kitchen paper can help to keep numbers down without harming other members of the ecosystem.
How to propagate Petunia
Petunias can be tricky to propagate and, given their relative low cost, most gardeners prefer to buy them afresh each year. If, however, you wish to try your hand at propagating them, cuttings in late summer/ early autumn can be an option.
- Find non-flowered shoots 5-10cm long and snip off the plant.
- Put them in a plastic bag straight away to prevent drying out.
- Fill a container with a compost mix which is at least 50% perlite (or if you prefer, as we do, 100% perlite).
- Trim the end of the cutting to just below a node (point at which leaves grow).
- Remove the lowest third of leaves.
- If the remaining leaves are large, cut them in half with a sharp knife (to reduce water lost through transpiration).
- Insert the cuttings into the compost and water lightly. Several cuttings can be put in the same container if there is enough space to do this without them touching.
- Place in a propagating unit with bottom heat if you have one or covered with a plastic bag on a windowsill or in a greenhouse if not (out of direct sunlight).
- Keep the cuttings misted and occasionally watered until they root. You will know this has happened when roots emerge out of the bottom of the container.
- Gently remove rooted cuttings and pot them into individual pots. Grow on in a warm, frost-free environment such as a conservatory, greenhouse, or sunny windowsill, until it is safe to plant them out the following May.
* Many plants carry Plant Breeders Rights and cannot be propagated for commercial purposes.
Common Petuinia questions
Are petunias easy to grow?
Spectacularly so! The advice given above will achieve best results, but in reality petunias are very tough and will tolerate a certain amount of neglect. They draw the line at drying out completely or being grown in full shade, but aside from this will have a good go at growing almost anywhere.
How long do petunias last?
In terms of flowering period petunias can bloom for up to six months of the year, particularly when deadheaded and fed regularly. Their overall lifespan is one growing season only, as they are either annuals or short-lived perennials treated as annuals.
What month is best to plant petunias?
Never plant petunias outside when there is still a risk of frost. For most of the UK this risk passes in May, though can be earlier or later depending on where you are. See our ‘When and where to plant petunias’ section above for more information.
What is the best fertiliser for petunias?
We recommend a high potassium liquid feed, such as tomato feed, to encourage flowering. See our ‘Feeding’ section above for more information.
How often should I water petunias?
As often as it takes to maintain a consistent level of moisture in the compost or soil. In a densely planted container, this might mean as often as once a day during hot weather. Follow our guidance in the ‘Watering’ section above to help avoid overwatering, which can be as harmful to plant health as underwatering!
