Close up of fresh spinach in an early spring garden

How to Grow Spinach

Spinach is a cool-season crop grown for its delicious leaves that can be eaten fresh in salads or cooked. It is important to plant spinach before the weather warms and the days are getting longer as it will bolt (flower) in the summer which will make the leaves bitter.  It can be planted again in the autumn when the weather cools and the days are getting shorter.

Sowing 

Because spinach is a cool-season annual it should be sown in the winter, early spring and in the autumn. When growing spinach in your Harvst it is important not to keep the tray too warm or have the grow lights on for too many hours. Light for more than 14 hours and temperatures greater than 24°C will cause spinach to bolt, flower, and set seed. As bolting equals the end of harvest, keep well within those limits.  The ideal growing temperature is 10-21°C.

Spinach is fairly easy to grow from seed and can be direct sown or transplanted later. It is a perfect crop to sow in your Harvst as it can stay in there till it matures or be transplanted outside. It can however be a bit sensitive to being transplanted so try to not disturb the roots too much! It can also be harvested as baby leaves or be left to grow bigger.

Seeds can be refrigerated for a week to speed up germination but with the right timings and temperatures in your Harvst it should not be necessary. Seed germinates in 5 to 9 days at 20°C, but can take up to 3 weeks to germinate if the soil is 10°C. 

Fill a tray with compost, a general peat free multi purpose compost will do as the seeds are quite big and do not need the more expensive seed compost. Water the compost first and then sow the seeds about 5-10cm apart and sprinkle 1cm of compost on top. Press down slightly to make sure that the seeds are in good contact with the compost. Carefully water again. 

Keep the soil evenly moist until seeds germinate because if they dry out they will most probably not germinate at all. This can be aided with a plastic dome over the tray but it is not a must.  However, as a general rule, the colder the soil the less moisture you need.

Plant care 

Keep the soil evenly moist throughout the growing season to grow spinach quickly but avoid splashing muddy water onto leaves if you can. Also keep them well fed as they’re very hungry plants.

Growing options 

You can choose from one of the growing options below or do a combination of 2, 3 or 4! 

  1. Baby Leaves: Start harvesting directly from your tray when the leaves are as big as leaves in a Supermarket baby spinach salad bag! If you pick one or two leaves of each plant from the outside, rather than the whole plant, it should keep on growing for a while and give you a few harvests! 
  2. Grow till maturity in your Harvst: When the seedlings have emerged, thin them to 20cm apart. This can be done by cutting the rejects with scissors (eat them in a salad!) or carefully using a stick/pencil to loosen the soil and lift the seedling up by its leaves and transplant to elsewhere. Make sure they are big enough to handle before you set out to do this. The compost will only have enough nutrients for a few weeks so you will have to feed the plants with an organic fertiliser throughout the growing season. 
  3. Plant outside: When the seedlings have developed their true set of leaves (not the first set appearing but the second set) they can be transplanted out into your garden. Space them 20-25cm apart in a staggered pattern or in a row about 30cm apart. If you have problems with slugs, keep them in your Harvst a little longer. A bigger plant can resist a slug attack much better! When planting outside it is best to make sure that your soil is great before planting by adding well rotten manure or other organic material so that it’s full of nutrients for your plants. If your soil is not great you can feed the plants with an organic fertiliser throughout the growing season because spinach is a hungry plant. When transplanting seedlings, ideally plant out early morning or evening and/or on an overcast day. Avoid planting at peak sun times or on windy days as this can cause sun or windburn which can lead to death! 
  4. Container Grown: Spinach can grow well outside in a container but try to choose one that is at least 20 cm wide and tall. As spinach is heat-sensitive, move containers into the shade on warm days and keep in mind that containers will warm quicker than garden soil in spring. Also, keep in mind that the compost will only have enough nutrients for a few weeks so you will have to feed the plants with an organic fertiliser throughout the growing season. 

Harvesting 

Spinach leaves can be harvested as soon as they are big enough to eat and it is up to you if you like the small baby leaves for a salad or larger ones for cooking! However, very large leaves can be bitter so harvest sooner rather than later. In any case cut the older outer leaves first and allow the middle younger leaves to grow on. When the days have more than 14 hours of light and the temperatures go above 24°C the plants will bolt. Make sure you harvest before that! 

Watch out! 

Spinach are generally pest free apart from slugs but can also be attacked by aphids, flea beetles, leafminers and spider mites. Aphids are best treated by showering the plants. Leaf miners tunnel through leaves and those should simply be removed. Also, look for the eggs on the underside of the leaves. Spider mites are best prevented by showering the plants regularly. When it comes to slugs it is generally best to plant out the seedlings when they are a little bit bigger as they can withstand an attack better.

Pro Tip

Don’t grow spinach through the summer as it is guaranteed to bolt! Even ‘bolt resistant’ varieties will at some point. Instead, grow New Zealand spinach or Malabar spinach.

Nerdy facts

Spinach is related to Swiss chard and its botanical name is Spinacia oleracea. It originated from Asia.

Recommended Varieties

Here are three great varieties but there are many more fantastic varieties to choose from!

Spinach Matador is a fast-growing and relatively heat-tolerant variety which is good for growing in containers and small spaces.

Spinach Medania  is a very popular, easy to grow and reliable variety

Spinach Giant Winter is one of the hardiest varieties and produces enormous leaves