Category: Greenhouses

Cold frames are four-sided boxes with transparent covers sloping towards the sun. You can buy readymade ones or easily make your own with new or recycled materials.  They are out of fashion nowadays because more people have tunnels or glasshouses, but still very useful.

You can use cold frames to hold plants for which there is no room in your greenhouse just now. They are good for hardening off vegetable plants or half-hardy annuals raised in the greenhouse before planting them out in the garden.  You can sow seeds earlier than possible outdoors if greenhouse space is not yet available, or quarantine new plants, or keep plants that need warmer or cooler conditions than you have in the greenhouse.  Cold frames are good for rooting cuttings, or warming up water or potting compost before use.  If you need an extra degree or two of frost protection for plants inside the greenhouse, you can put a lightweight cold frame over them for the night.

Cold frames are best placed near your greenhouse for convenience, and facing as near south as possible. Their south walls should be low enough to let in the sun.  To ventilate, prop open the downwind side of the top cover.  If you raise its upwind side, a gust could flip it off, and if you slide it the gap may be on the wrong side letting in chilling draughts.  It is harder to control their temperature due to their small volume, so you must anticipate the day’s weather and ventilate accordingly, closing the cover at night.  If you expect hard frost, lay a quilt of weighted bubble-wrap or sacks stuffed with leaves over the cover for extra insulation.  Water plants in the mornings to let the leaves and soil surface dry off before night.

We associate mangetout peas with early summer, but you can harvest them from April onwards if you sow them now. They are surprisingly hardy.  Sow about four seeds of ‘Oregon Sugar Pod’ or any other variety in four-inch (10 cm) pots of good compost and place them in your tunnel or glasshouse.  Protect them from mice until they germinate, and from slugs thereafter.  Don’t water them too heavily, and keep them covered with bubble-wrap or fleece at nights to speed up germination.  Plant them into a composted trench in the border soil when the plants are about 3” (8 cm) tall.  Push in short pea-sticks on either side of the row to support the plants and keep their growing tips off the soil surface, where slugs would eat them.  Ventilate well during the day to reduce mildew infections.  Cover over the rows at night with fleece or bubble-wrap to protect them on very cold nights.  Add in longer pea-sticks if the plants need them.  The plants should be ready to flower by April, and generous watering and some feed will help boost yield.  Harvest the pods often to keep the plants flowering.  You can sow a second, later crop to extend cropping until the outdoor crop comes in.  Enjoy!

Mibuna is a traditional Japanese green crop, ideal for greenhouses in winter. Like mizuna, it is a member of the cabbage family and produces green leaves for salads and cooking over a long period.  It is grown in much the same way.  It is less hardy and productive than mizuna, but its narrow strap-like leaves (often with a white midrib) have a more spicy flavour that gardeners enjoy and some slugs don’t (though some like it hot).  It can be harvested as whole plants, but excels as a cut-and-come-again crop.

Seed sown now in containers or borders can produce leaves from October to April or May next. Add in plenty of compost, and sow seed thinly in drills 1cm deep.  Border rows should be about 30cm apart.  Keep the soil moist: dryness encourages bolting, especially in spring-sown crops.  Watch out for flea beetles and slugs.  Cut off and compost overgrown leaves and any flowering stems that appear; it diverts the plant’s energy into growing more fresh leaves.  Use leaves while they are still young.  Eat them raw in salads or lightly steamed or pickled.

Image courtesy of GIY

This summer’s drought may make vegetables scarce and expensive until next year. Plan now to maximise the cropping potential of your tunnel or glasshouse and to leave no square metre unproductive over the winter.  It is too late to sow spring cabbage seed outdoors for planting out in the autumn, but raising plants in your greenhouse now may bring on seedlings faster and have them big enough to plant out on time.  If you do, harden them off before planting out and protect them from hungry pigeons.  Alternatively, plant them in the greenhouse for an earlier crop.  Plant single seed potatoes in large pots now, and they should still have time to mature before midwinter.  Beetroot, white turnips and kohl rabi will produce small but tasty roots, and you can eat their young leaves too.  Rocket, oriental greens such as Pak Choi, kale, winter lettuce, corn salad, Texel greens and winter purslane can be sown in succession for salads.  Calabrese, French beans and Florence fennel can all yield well in greenhouses from August sowings if the early winter is not too cold.

If your greenhouse is full already, bring on seedlings in cell-trays and then small pots until planting room becomes available. You can sow radishes, baby leaf greens and other short-term crops between rows of slower growing crops, as they will be harvested before the space is needed.  You can still have your five a day!

Sweet potatoes are related to morning glory and not ordinary potatoes. It’s possible and fun to grow your own.  Plants are usually raised from ‘slips’ taken from sprouting tubers.  You can sometimes buy them online or in a garden centre; ‘Beauregarde’ and ‘Georgia Jet’ (with orange flesh) and ‘T65’ (white flesh) are suitable varieties.  ‘O’Henry’ produces tubers close to its base and is good for container growing.

Bought tubers can be from varieties less suitable for Irish conditions, but you can still get a small crop from their shoots. Organic tubers unsprayed with sprout inhibitor are best.  Stand the tubers half-submerged in lukewarm water with their narrow ends down.  Place them in a warm sunny spot to sprout, changing the water daily.  Cut off the sprouts when they are about 15cm long.  If still rootless, root them in warm water or cutting compost and plant when rooted.  Soak bought-in slips overnight in lukewarm water before planting.

Plant them deeply (to encourage tubers to form at the nodes) in light, well-drained, fertile, neutral or acid soil in full sun. Always keep plants and tubers above 10°C/50°F.  Give warmed water when needed, and feed weekly with tomato feed.  Tie up the sprawling stems or they will root into the ground at the nodes.  Green leaves can be eaten in salads or lightly cooked like spinach, but don’t take too many or you will reduce the tuber crop.  Dig up the tubers after 3-4 months when the foliage turns yellow and dies back.  Avoid damaging them as they bruise easily.  Dry the roots in the sun for a few hours and then cure them for five days at 30-32°C / 85-90°F and 85-90% humidity.  Store them above 10°C/50°F in good ventilation and either eat them soon or blanch and freeze them.

As the whole country is bracing itself for the ‘Beast from the East’ we would like to advise customers with Polytunnels and Glasshouses that once it is safe to venture outside you should remove snow as it is surprisingly heavy and can collapse structures if allowed to build up excessively.

If you have an electric heater for use in Greenhouses (specially sealed for a wet environment) you could leave it running as the warmth may help to melt snow before it has a chance to build up.  If you have a direct fired heater – e.g. a gas heater that works like a gas hob inside a metal cover, only leave it running if you can be positive that there is a fresh air supply to it that will not get blocked (otherwise it will burn up all the oxygen and produce carbon monoxide with potential disastrous consequences).

Any number of ways (such as soft bristled brushes, sheets, mop handles etc.) can be used to dislodge snow but whatever you choose try not to damage your polythene or glass in the process, so use something soft so that it will not scratch (causing reduced light transmission) or tear the cover or break the glass.

It is also possible to prop the roof inside your Greenhouse or Polytunnel, but of course this should be done before snow builds on your structure in case it could collapse while you are in there.

We hope that everyone will be safe and well which is the most important thing, your Greenhouse or Polytunnel can always be replaced – and you may even have insurance to cover it, but of course it is not worth taking any risks to protect it.

You can buy carrots in the shops almost any time, but nothing beats your own early carrots for flavour and juicy crunchiness, harvested just before eating in spring. Carrots sown in a tunnel or glasshouse in February are ready to eat about late May, well before any crop sown outdoors would be ready.  In milder areas, seed can be sown in January for even earlier crops.

The traditional varieties such as ‘Amsterdam Forcing’ or ‘Early Nantes’ are as good as any for early sowing. Border soil for sowing carrots should be light, stone-free, without recently added manure or compost and above 5°C.  Sow the seed thinly in drills about a centimetre deep and 20 cm apart.  If the soil is very poor you could sow them in large pots of prepared compost or compost/soil mixture.  Cover the drills or pots with fleece on cold nights to keep the soil as warm as possible: the warmer the soil the faster they germinate and grow.  Protect the emerging seedlings from slugs, and as soon as they are big enough to handle thin them out to about five centimetres apart.  Do not let the soil dry out, as it stalls growth and the carrots can split when watered again.  If not eating harvested carrots right away, cut off the leaves to prevent them drying out and shrivelling the roots.

Things can be quiet in tunnels and glasshouses right now; cold weather, perhaps even still turkey torpor (lethargy) to turn your attention elsewhere. But you know that soon you will want to begin sowing new crops.  When you do, wouldn’t it be nice to just grab seed trays and pots and use them without having to clean them first?  It’s good to get them all washed together now so you can choose the exact pot you need and use it right away, and as they are all clean none can carry forward pests or diseases to the new crops.

Gather all empty pots, saucers, seed trays, tools and equipment. Bin any cracked or broken ones.  Place a big bucket on a stool or in a wheelbarrow to raise it up so that you don’t need to stoop.  Fill it with water (a kettle of boiling water can take the chill off) and add some (preferably eco-friendly) detergent.  Some like to add a bit of disinfectant but if you had no major pest or disease problems last year a good washing should be enough.  Scrub them well with an old washing-up brush, rinse them in a bucket or jet of clean water and leave them to air-dry.  To save even more time later, sort them by shape and size when stacking them away.

We at Polydome would like to wish all our customers, friends and suppliers a lovely Christmas and offer our best wishes for the coming New Year.

We will be closing on Saturday at 1pm and reopening on Tuesday 2nd of January at 9am.

The Polydome Team

If radishes were harder to grow, we might plant them more! Maybe because their fast and reliable growth makes them an ideal crop for children to plant, adults tend not to bother with them so much.  But if you are sowing green salad crops in autumn and early winter, why not enjoy some crunchy fresh radishes with them?

Sow the seed very thinly in drills about one centimetre deep and fifteen centimetres apart. The soil should be tilled finely with no clods.  Keep the soil moist and as warm as you can in winter, watering them when needed with water that has been stored a few days in the greenhouse to avoid chilling the plants.  Cover them with bubble-wrap on frosty nights, but remember to take it off again in the mornings.

Warm moist conditions and radishes are attractive to slugs, so take precautions against them: one slug can wipe out a whole row of seedlings in one night.

Some radish varieties are better than others for winter sowing under cover. Check the seed packet before you sow, but try some anyway – radishes are very accommodating and the seed is not expensive.