April 2024 Grow Me Now – Celery

A word of caution: (animal manures, compost, vermicast, and soil in general, can pose serious health risks. Learn how to use these garden additives safely before you begin working with them, especially when using them to make liquid manure plant feeds).

Super Celery!
Where would be without celery – at any time of the year – but especially over winter. It is an essential ingredient in slow-cooked comfort foods, provides a fresh, tasty crunch to cool season salads, and when stuffed with cheese, becomes a special snack that both children and adults can’t get enough of. Sadly, many tunnel house growers shy away from planting celery because they have had bad experiences with cultivating it in the past. Either it turns out to be bitter and stringy, or it bolts to seed before harvestable. Fortunately, growing celery isn’t at all difficult once you know how. And if, after reading the advice below, you still feel anxious about introducing celery to your undercover beds, we have a couple of alternatives that will tick the boxes (see the ‘tips’ section at the end of this blog).

Seed raising
Celery will perform well, but only on one condition – that you treat it like a king at all times. Just one slip-up, from seed to maturity, is enough to see it perform poorly. When you buy your seedlings from a garden centre or nursery, you don’t have control over the conditions they have been through. They may have been under- or over-watered, or been through very hot or very cold temperatures. All of which will affect the quality of your plants down the track. So, wherever possible, raise the plants from seed which you sow yourself.
To do this, sow seed into a seed-raising tray filled with quality commercial seed-raising mix, and cover it with a bare sprinkle of fine mix. Keep the seed raising mix damp, but not moist, by spraying it with water from a spray bottle. Germination takes place, ideally, when soil temperatures are around 21-25°C, so you may need to place your seed raising tray on a germinating pad if you are sowing at a cooler time of the year.
While you are waiting for the seeds to germinate (they take around 3 weeks to do so), fill single cell seedling punnets with potting mix (single cells makes for less disturbance at transplanting time). Unless you are experienced at making your own potting mix, choose a sterilised commercial brand so that there is less chance of introducing fungal disease to the tiny seedlings, and add to it an extra scattering of slow-release fertiliser pellets to it.
Once the seed have germinated, and the seedlings have developed 3 true leaves (leaves that look like those on an adult plant), it’s time to ‘prick them out.’ To do this, gently tease them out of the seed raising mix, using tweezers, and plant them (1 to each cell) into the seed raising mix. Be sure to plant the seedlings at the same depth they were growing at in the seed raising tray (certainly not any deeper).
Keep the seedlings in a sunny, sheltered spot, taking care not to expose them to temperatures of less than 10°C. If they do encounter cooler temperatures, or if they are allowed to dry out, the adult plants will likely run prematurely to seed once they are in the tunnel house.

Ground work
Come April, summer edibles have already spent months in the tunnel house, and by mid-autumn will have thoroughly depleted the soil you prepared for them back in September. Not only that, but as you have tapered off watering to assist with the ripening of fruit, the ground these plants have relied upon will be open and dry. Remove their spent summer growth, and before you replace them with anything else, water the ground deeply.
Deep watering involves applying a steady, light stream of water to the ground in an unhurried way, or turning on the sprinkler for half an hour or more. You can use a watering can for the job if you have strong arms. As a guide, use no less than 10 litres (two full, average-sized watering cans) of water for every half square meter of ground. Allow the moisture to seep in, then return 30 minutes later to repeat the treatment. Leave the soil overnight, then water once or twice again. You are now ready to add the hefty doses of soil additives that your celery seedling require for fast, unchecked growth.
Dig the tunnel house bed to a depth of a spade’s blade. As you do so, over the space of half a meter, chop in as much mature compost as you can spare (5 or 6 buckets, if possible). Also add 2 buckets of aged animal manure over the same area, a couple of handfuls of blood and bone, and a bucket or two of well-rotted kelp or seaweed.
Celery thrives in soil with a pH level of between 6.5 and 7.5, so, if your tunnel house bed has been set up for tomato plants, it will almost certainly need the addition of lime at a rate of 30-40 grams per square meter. Unfortunately, soil is slow to take up lime, so applying it at the time of planting your celery is unlikely to help. Don’t be concerned, because your celery will live without lime, and your tomatoes will appreciate the same space next spring, without it. Once you have dug all the nutrients into the tunnel house soil, water it twice, as above.
Lastly, prepare a concentrated liquid feed by soaking together for a week, in equal quantities, the following: chopped seaweed (seaweed extract can be purchased from the garden centre if you cannot lay hands on kelp), shredded comfrey leaves, and mature compost and/or vermicast. Note: if you don’t have access to kelp or seaweed, the same can be purchased in concentrate form from a garden centre. Dilute your liquid feed at a rate of 1 to 4 for use as liquid manure feed.

Transplanting
Gently tap the celery plants out of their individual cells (the best way to do this can be to up end the entire punnet onto spread fingers, supporting the little plants as they all drop out of their cells at the same time). Use a trowel or dipper to create pockets, 30cm apart in your prepared tunnel house bed, pop the seedlings in (without handling their roots), and gently firm the soil around them. Water around the base of each plant to settle it into position.
If you are not prepared to pick slugs and snails off the young plants after dark with the help of a torch, scatter low-hazard slug and snail bait around the seedlings, and keep children and animals well away from the area at all times.

Maintenance
Your aim, now, is to never let your celery plants dry out, or go hungry. Temperature is weather dependent to a large extent, but you can still try your best (by opening and closing doors, windows, and vents) to keep the tunnel house within an ideal celery growing range of 12-18°C. If severe frosts arrive, cover the plants (only for as long as necessary) with frost cloth.
Celery is a very hungry plant so, where safe to do so, apply liquid feed once a week, ensuring it does not touch the edible parts of any plants.

Care for your celery, perhaps more than you would for any other edible in the tunnel house, and it will reward you with thick, crisp, delicious stems and tasty, mild leaves.

Tips
Don’t be tempted to crowd celery seedlings. The stress it causes the plants can send them to seed before they mature. Keep to the recommended 30cm apart.

If you don’t have a germination pad (and even indoor temperatures can be cool in autumn), germinate your seeds, where it is safe to do so, on top of your hot water cylinder. Contain all water in drip-proof tray under the seed raising container at all times, and cover the container with clear plastic to lock in the heat. Check daily to make sure the seed raising mix remains damp. Remove from the top of the cylinder as soon as germination has occurred.

If successfully growing celery evades you, despite your best efforts, try growing ‘celery for cutting’ (Apium graveolens). This small-leafed, low-growing celery is harvested for its mild, celery-flavoured leaves and fine hollow stems. It’s make a tasty addition to soups, sandwiches, and salads.

Parcel is a herb alternative to celery that is easy to grow, and which thrives in a tunnel house over the cooler months. Use it as you would cutting celery.