Autumn Jump Starter 2023

Agrostemma (23 September 2023)

Easy to grow from both an Autumn sowing and/or a late winter sowing.

Autumn sown plants will flower from late May and will be slightly taller at 120-140cm.

Late Winter sown plants will flower around a month later and a tiny bit shorter 110-130cm.

Not quite as hardy as some of the seed varieties, but in our moderate UK climate Agrostemma grows quite happily in the shelter of an unheated greenhouse over winter.

We sow Agrostemma gracilis ‘Sensation Mix’ in exactly the same way. I’ll do some follow up videos for you shortly!

Euphorbia oblongata (22 September 2023)

Euphorbia oblongata is a short lived perennial so if you miss your sowing window you can try again in the Spring. Germination can be slow and erratic.

Never throw away the compost where seeds have not germinated.

You can get a sudden surprise months and months later.

This video includes a catch up on the plants started during the previous Grow-A-Long.

A short lived perennial, however once planted Euphorbia oblongata will grow bigger and bigger and gently self seeding, new plants will naturally choose ideal conditions in your garden so you’ll always have a new patch coming through.

Ammi visnaga daucoides (20 September 2023)

Extra video for the new variety of Ammi from this years Autumn Jump Starter Seeds shop!

Grow-A-long Ammi majus (20 September 2023)

Ammi majus is a hardy annual that is best sown in Autumn.

Very hardy, seed actually benefit from a bit of prechilling ahead of sowing, it really speeds up the germination process.

If you are looking for your seeds, they are in the fridge!

This video will take you on a journey from sowing the seeds all the way to blooming in June.

I will follow up with Ammi visnaga daucoides in the next video coming up shortly.

Grow-A-Long = I sow, you sow, from seeds to flowers together!

Grow-A-long Cornflowers (Centaurea cyanus) (18 September 2023)

Cornflowers are one of the easiest Annuals to grow and a brilliant one for the beginner gardener. As well as cut flowers, cornflowers are edible, use them to dress cakes or salads.

For best results Sow one seed per cell during September or early October while the temperatures are still warm.

Cornflowers will germinate and grow quickly so it’s important that if not started in a greenhouse, you move trays out where there is plenty of light as soon as seedlings emerge.

Note: although It is easy to trick cornflowers into germinating during the dark days of winter, it’s not a good idea, they will quickly become leggy and sickly. plants need to develop a good root ball before the nights cool.

Grow-A-Long Nigella (16th September 2023)

Following on from the Sweet Rocket and the Snapdragons Nigella is our next seed out of the box for the Autumn Jump Starter Grow-A-Long.

Watering Seed Trays

While the temperatures are still quite warm I like to water my seed trays from underneath. This fully hydrates the compost to stop it drying out as quickly.

Prevents seeds that need light for germination from being accidentally buried under the soil surface. Helps with wasting water. Helps prevent soil capping, this is where a hard crust or cap can develop on seed trays that are constantly watered. However once we move towards Winter trays will take much longer to dry out and over-wet compost will rot seeds. We will switch then to ‘spot watering’.

This is watering with a small can just the plants that need it.

New Mini Butterfly Snapdragons & sowing seeds in Quarter sized trays (13th September 2023)

If your greenhouse is still full of tomatoes and short on space then sowing in a quarter sized tray may be useful.

Snapdragon seeds are tiny and take a long time to germinate and grow (compared to Cornflowers for example), so it is important to get them going sooner rather than later.

Later on once the greenhouse is empty we can prick them out into 40 cell trays, you will also be able to make sure there are no empty cells taking up space in your greenhouse or cold frame.

Snapdragons (Antirrhinum majus), are technically a short lived perennial best grown as an annual.

I find that Snapdragons bloom best in their first year, especially from a Autumn sowing (Autumn Jump Start). Aging plants don’t flower as well and are susceptible to Antirrhinum rust (Puccinia antirrhini).

Plants can also be wiped out by a very cold winter. I sow seeds twice, once in Autumn and then again in late Winter for flowers from late Spring to late Summer.

Sweet Rocket (Hesperis matronalis) (12 September 2023)

This is the first seed that we are going to sow for the new season Autumn Jump Starter. Sweet Rocket (Hesperis matronalis) is a biennial and can be sown in the summer, but I find it a lot less hassle to grow with the hardy annuals.

Not all biennials respond as well to being sown in Autumn but this one has never let me down.

To chill or not to chill

I thought you might appreciate a video for this!

There is no hurry to start sowing, we are best to wait until this heatwave is over… otherwise you might have problems with germination, seeds getting frazzled and knocking some of the hardiness out of your plants. You then might have to resow later putting you up further behind than if you waited.

In the meantime just enjoy the weather, the flowers are thriving, it’s been an excellent year for Dahlias!

You can also keep yourself busy washing your greenhouse to clean out any pests and diseases before the new plants go in and maximise the light by clearing any green algae and dust from the windows, this will make a real difference as light levels dip.

Welcome to the Autumn Jump Starter Grow-A-Long 2023

Getting Started

You can watch all my Shopping List Videos here:

Ahead of our seed sowing Marathon I thought we’d just have a quick chat about compost

Autumn Jump Starter Video 2 – Compost

While the temperatures are still quite warm I like to water my seed trays from underneath.

This fully hydrates the compost to stop it drying out as quickly.

Prevents seeds that need light for germination from being accidentally buried under the soil surface. Helps with wasting water. Helps prevent soil capping, this is where a hard crust or cap can develop on seed trays that are constantly watered.

Watering Seed Trays (from underneath)

Getting started

Fill seed trays or cells to the top with soil, tapping gently as you go so the soil settles and there are no trapped pockets of air and water. 

You can place in a tray of water to moisten but not soak. You can also overhead water but do this before sowing so you don’t dislodge your carefully sown seeds.

Compost mix should be thoroughly damp, but not dripping wet.


Get your label ready, you forget very quickly what you have sown so write them first.

Sow seeds according to the instructions, a general rule seeds requiring darkness for germination should be sown twice as deep as the seed is large. Make a small hole with a pencil or dibber.

‘Dust like’ seeds are sown on the soil surface and often benefit from light to germinate.


Sow 1 or 2 seeds to each cell, you can remove the weakest if both germinate later.

I do not use heated propagation mats for Autumn starting or propagator lids. The Autumn greenhouse will naturally be warm and humid enough.


Check seedlings daily and water (from underneath if possible) when the soil appears dry. this is very important for seeds needing light for germination. The watering could push them below the soil surface into darkness. This will then prevent germination.


No matter how carefully you sow, extra seeds will appear and you must remove these extra seedlings, if you don’t your seedlings will be cramp and crowded and won’t have the space to grow on well.

Some seedlings resent root disturbance such as Larkspur and Nigella and are not suitable for pricking out.

Swan Cottage Flowers Seed Sowing and Propagation Workshop and Classes

As young plants grow, they need to be fed. Liquid seaweed is a gentle water on feed suitable for young plants.

Eventually your seedlings will outgrow their trays, we will start poting on into a larger cells or pots in late Winter.


Be care not to mother your plants too much, this can reduce their hardiness. On warm days even during winter open the greenhouse. Ait flow is vital for a healthy environment.

Before planting out in late Winter / early Spring we will harden plants off by setting trays in a sheltered spot outside, increasing the amount of time they are out each day.

This helps the young plants acclimatise to outdoor temperature fluctuations and toughen the leaves so they can cope with the outside environment. Failure to do this can cause plants to go into shock.

Watch out for greenfly, slugs and snails. your newly sown plants will be full of delicious sappy growth. They can be mown down overnight.

This page will be updated every week during the growing season so you can follow along in real time.

Detailed variety specific information of all the steps from seed to flowering is contained in our Grow-A-Long handbooks.