Best Time to Sow Seeds

When growing a garden you can choose to either buy seedlings from a local nursery or garden center, or you can choose to grow your plants from seeds.

While it is more labour intensive, sowing seeds is cheaper and provides a great sense of accomplishment to many gardeners as they can see the entire process of growing food from seed germination to harvest. Care must be taken to sow seeds correctly whether it be indoors in trays, directly into the soil outdoors, and done at the proper time -- all variables dependant on the individual vegetable varieties.

Growing season in the United Kingdom

The typical growing season in the UK begins in April or May when soil temperatures begin to warm up and extends through until October or November.

Southernmost areas experience slightly warmer climates and the gardening season may start up to 2 weeks ahead of the central area. On the other hand, the start of the growing season in northernmost areas can be up to 2 weeks behind the central region.

This fluctuation in climates mean there is the potential to be a lag of a month between when the growing season starts in the southern part of the United Kingdom compared to the north, affecting the planting dates in the different regions.

Sowing Times for Different Seeds

When thinking about sowing seeds, it’s important to take two aspects into consideration: how long it takes plants to mature from the time seeds germinate, and what ambient temperatures mature plants prefer. Temperature needs to be considered since it affects harvest; do plants prefer to be harvested in cooler seasons, do plants need the heat of summer to grow well, or do plants grow well regardless of the temperature changes?

In terms of when to sow seeds, plants fall into these two main categories:

Seeds that need to be sown indoors before the growing season starts,

Seeds that can be sown directly into the ground.

Some of the common garden plants are categorized below, and dates given for when you should sow seeds (these recommendations are based on the central growing region, adjust for your specific location).

Sowing seeds Indoors

Some plants have a slightly longer growing period than the actual growing season. If they are frost tender then they can’t be planted outside before the chance of the last frost passes; to get them to maturation seeds need to be started indoors, under cover and then seedlings transplanted outside when the soil temperatures permit.

Artichoke, aubergine, and celery seeds prefer to be started indoors mid February to the end of March.

Both broad and french beans do well if you sow seeds in January/February and then transplant outside in April.

Peppers are fairly slow growing; start seeds in February or March to move plants outside in May.

Tomatoes have one of the longer growing periods and do not like frosty temperatures. Start seeds indoors under cover in late January or February to have them ready to move outside in when the chance of frost is gone.

Sowing seeds Outdoors

Plants that tolerate having seeds sown directly into the ground fall into further categories, based on exactly when in the growing season you should sow them.

Early Season

There are a fair amount of plants that can tolerate cooler soil and air temperatures, and even survive a light frost.

These seeds can be sown directly outdoors before the rest of the garden can be planted.

• Beetroot seeds should be sown anytime starting in mid March through June. Plants grown in the cooler months will be sweeter and more tender.
• Broad bean can be planted directly in the ground mid February to late March.
• Brussels sprouts can be started under cloches in early March and left covered until May for a September harvest.
• Cabbage seeds should be sown in mid March through April, regardless if summer or winter variety.
• Carrot seeds can be planted as early as February, if the ground isn’t frozen, with successive plantings through June.
• Parsnip likes to be sown in late February through April for a late fall harvest.
• Pea plants are another early season plant; sow seeds late February through June for continuous harvests.
• Turnip seeds can be planted late February through until September, with later plantings ready for harvest just before the ground freezes.

After Last Frost Threat

Plants that grow quickly, and thrive in the heat of summer can be sown directly into the soil after the last threat of spring frost has passed.

• Courgette seeds should be sown in late May or June and then covered with cloches for 2 weeks to promote germination.
• Cucumber likes to go into the ground in May after the temperatures warm up.
• French bean can be planted directly into the garden in May or June.
• Sweet corn loves the heat of summer and grows quickly.

Sow seeds in May or June for a late summer/autumn harvest.

Sow seeds anytime

Surprisingly, there are a handful of cold-tolerant plants that can handle being sewn directly into the ground anytime of the year.

During the colder winter months plants may benefit from the protection of a cloche or cold frame.

• Cauliflower can be planted anytime if using the “All Year Round” variety. It is one of the easiest types to grow and produces big, tight heads.
• Leafy greens (lettuce, rocket, swiss chard, spinach) prefer cooler weather, and will tolerate winters. In the hot summer months they benefit from dappled shade or shade cloth to keep them from bolting.
• Spring onion seeds can be sown early in the spring, or planted later in the fall and the onions allowed to overwinter in the ground.
• Radishes are one of the quickest plants to go from seed to harvestable fruit. When temperatures are optimum they can be ready to harvest in 3-4 weeks from the time of planting.

What Month is the Best Time to Plant Vegetable Seeds?

Knowing when to sow seeds for your garden, and whether they need to be sown indoors or can be directly planted into the soil is critical for making sure they germinate, and plants have enough time to mature before the growing season ends.