Growing leeks indoors for a healthy harvest

Delicious leeks are the mildest flavoured members of the onion family (and if you didn’t know, also the national emblem of Wales).  

I love leeks for their versatility as much as their flavour. They’re great in soups, casseroles, pies, risottos and many more tasty things – especially where cheese is involved. Pretty much wherever you can use an onion, you can switch it for a leek.

For indoor gardeners, it’s perfectly possible to grow a good amount of leeks indoors to enjoy over winter. A decent sized trough planter on the windowsill will give you at least 2 rows – 3 at a push.

Plus, when you’ve eaten them you can grow more leeks from the leftover scraps (more on that later)!

What you need to grow leeks indoors

Providing you have a windowsill that gets plenty of light (south facing is best), you won’t need any special equipment. If you don’t have a well-lit spot, you can get around it by using grow lights, but I’ll cover that another time.

All you really need is leek seeds/seedlings, a planter at least 9 inches deep, some peat-free multipurpose compost and a watering can.  

If you’re just starting out and don’t want to spend too much, you can get creative with the planter. 

You could grow your leeks in any container that’s deep enough and has a decent surface area. So that might be an old crate, half a barrel, a catering size coffee tin – whatever you can lay your hands on. 

Just be sure it’s good and clean, hasn’t been used for any nasty chemicals, and will fit somewhere!

The same applies to the watering can – you don’t need to buy one. You could rustle up your own from a screw-top plastic bottle, making small holes in the lid to produce a fine spray.

Now let’s get to the nitty gritty of how to grow your leeks.

Growing leeks indoors from seed

Sowing your seeds

You want to sow your seeds early in spring (March/April) to have leeks ready for a winter crop. Leeks typically need a long growing season – about 140 days from sowing to harvest.

If your planter doesn’t already have them, you’ll need to make some drainage holes in the base. You only need a few and they don’t need to be too big – about 1cm. 

If it didn’t come with a tray or saucer, you’ll want something non-porous to stand it on to collect excess water. But don’t worry too much if you don’t have anything suitable. 

You can always move your planter to the sink for watering instead, bringing it back to the windowsill once you’re sure it’s dripped dry.    

Fill the planter with compost to about 2 inches from the top, give it a good water, then sow seeds thinly on the surface in rows. Ideally, leave about 2-3 inches between seeds. 

You’ll have to thin them out as they grow, so you don’t want to have to discard too many. But it’s best to sow more than you need in case they don’t all germinate.

Sprinkle compost lightly over the seeds, just enough to cover them, and firm it down gently with your hands. Make sure the seeds have good contact with the compost. 

The seeds will usually germinate in 10-14 days. Once they reach an inch or so, thin them out to leave 6 inches between seedlings. 

Want to grow more indoor veg? You might also like: How to grow radishes indoors.

Growing temperature

Unlike peppers, aubergines/eggplant, etc, leeks aren’t a particularly heat-loving crop. They’re best grown in daytime temperatures of around 55-70°F, dropping to 50-55 degrees at night. 

Most homes tend to naturally fall somewhere in the 65-70°F range, which should be perfectly fine for your leeks. 

In very intense summer sunshine, you may want to move the planter away from the window to prevent the leaves from scorching. You could also use a slatted blind or some sheer fabric to help diffuse the sunlight. 

Watering needs

Water your leeks enough to keep the compost moist but not wet. Push in your finger and if it’s still damp an inch below the surface, don’t water yet. 

Water in the morning and use tepid water rather than cold. Being raised indoors, these crops will be more tender than usual, so ice cold water would be quite a shock!

Give the compost a good glug, but not so much it pours out of the drainage holes and leaches out precious nutrients.  

When you’re watering, aim for the soil around the leeks and try to avoid wetting them. The window will act as a magnifying glass to any water droplets and can scorch your crop.

Fertilising

The compost will contain enough nutrients to last your leeks a good while, but as they grow and the compost depletes they’ll need a little extra help.

Apply a nitrogen-rich liquid feed every now and then when watering. Something like a seaweed-based fertiliser is ideal.

Follow the advice on the bottle for the right strength/frequency. Resist the temptation to over-feed as this can make mineral salts accumulate in the compost and do more harm than good. 

Humidity

Unless you’re growing your leeks in the bathroom (unlikely), the air indoors is probably going to be on the dry side.

In centrally heated homes, relative humidity (the percentage of water vapour in the air) can drop to 20% or lower.  

Vegetables prefer much higher humidity – anywhere from 50% up to around 80% – which is one of the biggest differences when growing indoors vs outdoors.

Your indoor leeks will be much healthier and happier if you take steps to boost the humidity in the room. 

A simple way is to place several bowls of water around the room, particularly close to radiators. You can also give your leeks a daily mist with tepid water.

If you plan to do lots of indoor farming, treating yourself to a humidifier might be a good investment – especially if you’ve got humidity-loving houseplants too.  

Growing your leeks from seedlings instead

It’s a little quicker and easier to grow your leeks from shop-bought seedlings. If you’re pressed for time, you’ll find ready raised seedlings easily enough at a plant nursery or garden centre.

All you need to do with these is get your compost-filled trough and make holes about 6 inches deep and 6 inches apart. A pencil is perfect for the job.

Drop in your seedlings, one in each hole, then fill the space around them with water (not compost!). Carry on caring for them as above.

Preparing your leeks after harvest

Your leeks can be harvested early for a smaller, sweeter crop once they reach pencil thickness. These young leeks make a great substitute for spring onions (green onions/scallions) in stir fries and salads. 

However, if you want more bang for your buck, leave the plants to mature and thicken into more substantial stems. 

If you’re used to buying shop-bought leeks, those are a little cleaner than your homegrown crop will be. After picking give them a thorough rinse, making sure you don’t leave any compost lurking between the leaves.   

Trim off the straggly tops (you can freeze these to use in vegetable stocks) and use the main stem in your cooking. But save the ends with roots and you can grow more leeks for free!

Growing leeks indoors from scraps

This really appeals to my thrifty side. Regrowing a whole leek from a scrap feels like magic – but is actually quite easy. Check out this little video to show you how to regrow leeks in water:

All you need is a 2-inch piece of stalk with the roots intact. Drop it in a glass, add tepid water to cover about half the stalk and place on a sunny windowsill.

Within a few days, you’ll see a new leek shoot emerging from the centre of the scrap. Replace the water with fresh every couple of days and the leek will keep on growing. 

In 3-4 weeks, you’ll have a ready-to-use leek right there in the glass. If you want it a little bigger and thicker, peel away the outer leaves that have been sat in water, pot it up and grow it on as above until it reaches your preferred size. 

So there you have it. No garden? No problem – you can grow fresh vegetables in very little space, right in your home. I hope you feel inspired to get growing leeks indoors!

Photo by ohefin on Foter.