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Basil originated in tropical regions of India and Southeast Asia and there's a clue in that as to what conditions basil prefers throughout its life, from seed germination to harvesting. It likes warm conditions! It also does not do well in windy conditions.
Basil seeds
To germinate basil seeds, a temperature range of 70°F / 21°C to 80°F / 27°C is ideal. For this reason it's only really practical to sow the seeds indoors. A heated greenhouse might be OK but it will be very expensive to heat it to that temperature in spring.
With the above in mind, our recommended timings for growing basil from seed are:
Sow basil seeds (indoors) in the first week of April in average UK areas.
Thin out basil seedlings in the last week of April in average UK areas.
Harden off basil starting in the third week of May in average UK areas.
Move basil to final full sun position in the first week of June in average UK areas.
Begin to harvest seed sown basil in the first week of July in average UK areas.
Unless you want to grow basil on an industrial scale we suggest sowing seed in 8cm / 3in pots. It saves all the effort of transplanting them when they outgrow smaller pots and it works just as well.
Fill the pot nearly to the top with good quality general purpose compost and place four or five seeds on the surface of the compost. Very gently press the seeds onto the compost surface and then sprinkle a small amount of compost over the top of the seeds to just cover them. Lightly pat the compost down with your fingers.
Place the pots in a tray of lukewarm water for half an hour or so to allow the compost to absorb the water. Move the pots into another dry container.
Gently cover the individual pots with cling film, just enough to stop the majority of water evaporation but also allow some air to circulate. Place the container in a room which will have temperature of approximately 70°F / 21°C for most of the time.
At this stage light is not important so the tray can be placed on the floor if you prefer. The seedlings will take anything from three to ten days to emerge.
As soon as you see the seedlings emerge from the soil surface, remove the cling film. Place the pots on a draught free windowsill or somewhere that receives a decent amount of light. Try to maintain a very minimum temperature of 15°C / 59°F, preferably a little higher.
As the basil plants are growing you will notice that they grow towards the light. So every day or so turn the pots round to encourage the stems to grow straight up.
When the seedlings reach about 5cm / 2in high , identify the strongest growing one and gently pull out the other seedlings leaving only the strong growing one in the pot.
Up until the point when you begin to harden off the basil plants outside (see below), the basil plants should be watered sparingly and preferably by placing each pot in a tray of water for 15minutes or so to allow it to absorb the water from the base of the pot.
The compost the seeds were sown in will contain all the nutrients the growing basil plants need over the next eight weeks so don't add any liquid feed until the plants are growing outside.
Basil is unusually temperature sensitive and they also dislike windy conditions. For this reason they need to go through a hardening-off process for a week or two after they are first placed outside.
When you first start to harden-off a basil plant, do not expose it to prolonged full sun at first, do this gradually.
Start to harden off basil seven to eight weeks after the time we recommend sowing the seed - see the calendar at the beginning of this page. On this basis, start hardening-off basil grown from seed in the third week of May in average UK areas.
Start thinking about planting out your basil plant around the first week of June in average UK areas. Always err on the side of planting out a week or two later if you have any doubts about the strength of the plant or the weather conditions.
The two options you have for planting out basil plants are to either plant it into a larger pot with the idea of growing it in pots for its life or to plant it into a prepared bed in open ground.
The option I choose each time is to grow basil outside in pots / containers. I aim for an eventual pot size of around 25cm / 10in. This will require potting up the plants in two or three stages. Place the pots in a full sun position protected from strong winds.
Planting basil out in open ground seems pointless to me. Three plants will supply all your needs for fresh leaves with plenty left over for drying to last over winter and spring.
Watering basil plants in containers growing outside involves keeping the compost moist but not waterlogged. How often this is required will depend on weather conditions.
As far as feeding basil is concerned, basil requires minimal feeding. Once a month when you water basil add a small amount of general purpose liquid fertiliser. Do not use tomato feed, this will only encourage flowers which in turn will reduce leaf production.
Pruning basil plants improves their health considerably and should be done regularly whether you need the leaves or not. Harvesting basil is achieved in the same manner but you will only do this when you need some leaves.
Every week or so examine your plants to identify any stems which have four or more leaf nodes on a stem. A leaf node is the point at which a pair (although sometimes only one) of leaves are attached to a stem. See the picture below where we have cut part of a stem to identify what a leaf node looks like.
Basil Plant Leaf Node
The area in the white circle, where two leaves join the stem, is the leaf node. If you look carefully at the circled area (click the picture to enlarge it) you will also see that two very small shoots have sprouted between each of the leaves and the stem. These will grow into new stems.
Prune each stem leaving just two leaf nodes remaining. This will encourage the plant to produce more stems and at the same time, stop the plant growing weak and leggy stems.
Note that when your basil plant, grown from seed, is young it will have just one stem. As soon as that stem reaches four or more leaf nodes it's time to prune it.
It may sound harsh but by pruning that stem the plant will grow two stems from each of the remaining leaf nodes. And that's the way to grow a healthy and bushy basil plant from seed - each time you prune it you will be rewarded by two stems instead of one.
To harvest basil leaves don't simply pull off the leaves. Instead, prune as many stems as you require using the pruning technique described above. The pruned stems / leaves can be put into a bowl of water for an hour or so until they are required, at which point the leaves can be pulled of the stems for use.
To store basil leaves they can either be dried or frozen in water. Click here for some ideas on how to preserve basil leaves for many months.
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