As the weather warms up, I’m itching to start growing again and it’s tempting to start as soon as possible but there are good reasons for sowing a bit later in the year. I’m going to focus on sowing under cover, as this is the method I use for the majority of my annual flower seed. The other option is direct sowing where you sow straight into the soil outside but you must wait for the soil to warm up for this.
Sowing under cover means that you gain a head-start and will get earlier flowers. You don't need a greenhouse or potting shed for this. I use my windowsills and using 2 windowsills, I have space for all the annuals that I grow. By having my seedlings in the house, I can keep an eye on them so that I don't forget to water them and turn the pots each day. You can also protect your seedlings from being munched by slugs and other pests, until they are larger - larger plants are more able to withstand a bit of nibbling.
Q. When should I sow my annual flower seed? - (every packet seems to have slightly different timings!)
A. When it comes to sowing, day-length is more important than warmth. If you sow too early, your seedlings are likely to become leggy from straining for the light by the time you plant them out.
The first thing to do is to split the annuals you want to grow into hardy* and half-hardy** types to simplify things. Then, sow all the hardy seed from early - mid March and all the half-hardy ones from early April. You can also sow at any time throughout the spring and summer so if you miss sowing in March and April, you can still have flowers this season, they’ll just appear later.
As long as there is time for them to grow and flower before the first frost, you can sow annuals at any time. I sow a 2nd batch of hardy annuals when my first batch start flowering, so that once the first batch have flowered for 2-3 months, I have plants to replace them with. Using this method, I have a continual supply of flowers from late May until the first frosts.
*Hardy annuals are just that, hardy - meaning that they’ll survive winter cold and wet and withstand a frost.
**Half-hardy annuals cannot withstand frosts and so need to be planted out after all risk of a frost has passed. This is generally mid-late May in this area, so if I sow at the beginning of April, I know that my plants will be the perfect size for planting out when the warmer weather arrives.
Hardy annuals can also be sown in late August - October for early flowering the following year. They go into a semi-dormant state through the winter, coming into growth again in the spring. Sweet peas, Cornflowers and Ammi all do well with this method.
Q. Do I need special seed compost?
A. Seed compost is specially formulated for growing seeds but for me, a good multi-purpose compost is less expensive and performs just as well. Trials have shown that multi-purpose can be really good and the good ones had less peat than the top rated seed compost in a recent Which? trial. Peat-free options generally performed less well but they are being improved all the time. Whichever compost you use, break up any large lumps and fill your seed trays or pots loosely to the top before firming it down gently – the bottom of another tray/pot can be used to press it down. Leave a small gap at the top for watering.
Q. How deep do I sow the seed?
A. Seeds vary in size, generally, larger ones like sweet peas should be buried under about an inch of compost and smaller ones just need a fine sprinkling of compost over the top. Very fine ones like poppies can be left on the surface.
Q. Should I use trays or pots?
A. Seed trays can be useful for small seeds where you want to sow a lot of one type of seed. However, I find that I don't want to grow more than 3 or 4 of each type of annual in my cutting beds so to make things as simple as possible, I sow all my seed directly into square black plastic 9cm pots. This is the ideal size to house seedlings for up to 6-8 weeks, without getting root-bound, which is a good size for planting out and prevents the time-consuming need to prick them out and pot them on.
I plant 2-3 seeds per pot (or a small pinch of very tiny seeds) and pull out all but the strongest seedling once they emerge). 8 of this size pot fits nicely into a square seed tray that acts as a reservoir for water. The tray fits perfectly on to my windowsills and means the whole tray can be easily turned every day to prevent seedlings growing towards the light. I also happen to collect large numbers of this size of pot as it’s a popular size for garden perennials to be housed in when you buy them from the garden centre. At Miles Garden Design, we are left with lots of this size pot left at the end of a planting job so, for me, they are essentially free - lucky me! You may be able to get them for free on sites like Freecycle or you can buy them fairly cheaply on the internet. You can re-use them, making sure that you clean them thoroughly at the end of each year.
Q. How often should I water my seedlings?
A. Water the compost well before you sow the seeds, rather than after sowing, so that you don’t dislodge the seeds or wash off the covering of soil. Check pots daily and water sparingly with tepid tap water. Don't use water from a rain barrel as it may harbour diseases and small seedlings are vulnerable. Use a small watering can with a fine rose. Keep pots moist but not wet.
Other seed sowing tips
Labeling. Label all your individual pots or seed trays as it is very easy to lose track of what you have sown. I use sturdy multi-coloured plant labels and use a black wax pencil to mark them. At the end of the season, you can scrub off the writing with a sponge scourer and some washing up liquid and re-use them. I like using coloured ones as you can use a different colour for different plants in each tray so you can immediately see how many of each type you have. Plus, they look pretty.
Create a list, use fresh seed. Have a plan for planting up your annual cutting bed and a list, so you know exactly how many of each plant you need to sow. I generally only grow 3/4 of each type of annual and actually don’t need much seed from a packet. Spare seed can be shared with friends or stored for using the following year but do check expiry dates on packets as the germination rate does go down, the older the seed is. If you are unsure, you can perform a simple test to see if the seed is still viable.