Extend the growing season with a hotbed

Other people's gardens are always full of good ideas and inspiration, and few more so than Barnsdale, the garden of the late garden writer and presenter Geoff Hamilton. This 8-acre site is home to Hamilton's extensive kitchen garden and around 38 demo gardens or garden rooms. On my last visit I was particularly taken with the hotbeds in the kitchen garden.

I've been interested in hotbeds since reading of the Victorians' enterprise in building them to grow tropical fruit such as pineapples. But Barnsdale also demonstrates something else: the use of hotbeds to extend the growing season, getting seedlings off to an early start; as a nutrient-rich environment for hungry crops (courgettes, squash, beans, cucumbers) later in the summer, and then as a generator of well-rotted manure for the following seasons.

I've recently embraced the no-dig system of vegetable gardening with all the zeal of the convert, which means I need more and more compost, or manure, or organic matter generally, to cover new beds and top up existing ones. Buying it in each time would become very expensive very quickly. The obvious answer is to generate one's own. The vegetable compost heap is a rich source of - free - organic matter, and a hotbed adds an efficient - and free, again - source of manure.

The base of the bed is a four-sided box - I made my first one from leftover composite decking and a second one from gravel boards. You can then place a cold frame on top - again, either one you have already, or a DIY job. My DIY cold frame was made with more decking - softwood, this time - with the side boards cut diagonally lengthways to create a sloping lid. You can just see this in the picture, and the cold frame is positioned so that the angled top faces south to catch the best of the sun. I saved our two big double-glazed bathroom windows from our house renovation and these make a well-insulated glass lid. (Although they are rather heavy.)  

Position the cold frame on the base so that the glass cover faces south, if possible, to get as much light and warmth as possible in colder months. 

                                                

       

Hotbed number two, made with deckboards and lined with black plastic to help with heat retention.

The base is then filled with fresh - not rotted - manure. You may be able to get a local farmer or stables to deliver this, but for me it's a visit to the local stables to load the car up with bags full of fresh manure from the muckheap. Again, it's free, which is largely the point of doing it this way, but I do have to factor in the cost of having the car valeted afterwards. The smell lingers on a bit.

Once the base box is full of fresh manure and you've tamped it down to ensure the box is properly full, put the cold frame on top and fill with compost to a depth of around 5cm. Then fit the lid over the top and leave the manure for a week or so to settle. The contents will heat up under the glass and begin to rot down. You will probably find it sinks quite a bit in just a fortnight.

Top up with more compost to about 10cm depth, and from mid_January you could be ready to start sowing seeds for an early harvest. Sow thinly directly into the hotbed compost and keep the glass lid  on until they have germinated. Depending on the weather, I will start lifting the lid to ventilate the bed once the true leaves are showing, but will replace it at night and if temperatures drop.

I've sown salad leaves, lettuce, rocket, lamb's lettuces, radishes and Chinese broccoli in the hotbed in the third week of January and been eating fresh salads 4-6 weeks later. The beauty of the cut-and-come-again salad leaves is that you can keep cropping them all the way through until the summer.

Once the salad leaves begin to bolt in midsummer, you could re-sow, but instead I pop in a couple of courgette plants and watch them romp away as the roots reach the manure gently decomposing under the thick compost layer. Two courgette plants will grow to fill a 100cm x 75cm hot bed and provide plenty of courgettes throughout the summer and autumn.

 Other greedy crops such as squash, cucumber and beans could also go in the bed in summer. 

In autumn, once the courgettes have gone over, lift out the plants and chuck them on the compost heap. In the hotbed you should now find a thick layer of fabulous well-rotted manure ready to be dug out and used on the next season's growing beds.

And once the hotbed is empty, you can start all over again with a visit to the local stables ...

Salads in a box - reuse the recycling bins

Mixed leaves in an old recycling box: red mustard, green-in-snow,
tatsoi, mustard frills and komatsuna

I’m always on the look-out for different containers for plants. I’ve grown oriental leaves in the wooden crates used to deliver veg to the supermarket, I’ve raised microleaves in the shallow plastic trays used for packaging fruit and veg, I’ve grown herbs in a makeshift vertical garden using an over-the-door shoe-holder, and as an allotment owner, I am well-versed in the art of making raised beds out of pallets. Often these containers are more convenient than conventional pots: round isn’t always the best shape if you’re growing a mix of things in the one pot.

Last year our local council gave us wheelie bins to use for throwing out items for recycling, to replace the two 55-litre capacity boxes we’d had previously – one for newspaper and bottles, the other for everything else. No-one appeared to be responsible for taking away the old boxes, so I collected up the ones in best nick and have found they make excellent seed beds (I started off both leeks and chicory in a recycling box this year), and are particularly good for growing cut-and-come-again salad leaves. With a box kept just outside the back door, I have a variety of leaves available whenever I want them.

If some of the plants start to bolt or if they just look straggly, I’ll pick one last harvest, uproot them and sow the next batch.

Right now, with the long days and the night temperatures beginning to warm up, they will germinate quickly and give you edible leaves in about four weeks. But you can sow seeds for salad leaves at just about any time of the year. In winter, growth will be much slower and to keep your salad box going you will probably need to protect the box with a cloche or fleece.

Carrots grown in a box - seeds sown in March directly
into seed compost, then covered with vermiculite.

To start with you need to source your box. Choose one in reasonably good nick and wash it thoroughly. Next you will need to make some drainage holes in the bottom. Then it needs to be filled with compost. Our recycling boxes are 40cm deep – rather deeper than the salad roots will go down, so rather than waste good compost buried at the bottom of a recycling box, I spread gravel or small pebbles along the bottom, to help with drainage, and then add a layer or two of leaf mould, spent compost or mulch – any good organic matter to fill the box up halfway. Then I top up with fresh seed compost.

Before sowing, water the compost thoroughly. Then scatter the seeds thinly on top of the compost – you can mix seeds randomly or sow different varieties in blocks or thin lines, as I have in the photo. Finally sprinkle a very fine layer of seed compost over the surface so the seeds are just covered. At this time of year, you don’t need to cover the box to keep the seeds warm, but if you’re sowing late in the year or in early spring, you can cover with a clear plastic propagator lid if you have one, or with horticultural fleece (I have also improvised with an insulating cover of clingfilm in the past, when I haven’t had either a lid or any fleece to hand).

You may also need to protect your salad seedlings against slugs and snails if these are a pest in your garden. I run a strip of copper tape along the rim of the box: the molluscs won’t slide over copper as it reacts with their mucus. My particular pest in recycling box beds is my own cat, who likes to either sleep on them, flattening the seedlings, or, worse, using them as a litter tray. A square of plastic mesh over the top, fixed with net pegs, keeps him off.

Salad days

 At this time of year I start to think longingly of the new season’s vegetables. We’re eating up the last of the winter roots and greens somewhat wearily now. The leeks are all finished as are the parsnips and cabbages – still a few maincrop potatoes in store and a never-ending supply of cavolo nero.

This ‘hungry gap’ between the old year’s produce and the new makes me very thankful for the mixed salad leaves which are giving us some variety on our plates. From oriental leaves like mizuna and mustard to lettuce seedlings picked as single leaves, a pot of mixed leaves on the windowsill will keep us going until the soil warms up and we can grow lettuces outside.

Usually I throw together some leftover salad seeds from last year to make my own leaf mix, but back in January I was distracted by a 2 for 1 offer in a local garden centre and came home with a Speedy Mix and a Winter Blend from Thompson & Morgan to add to a packet of Marshall’s Salad Finest Mix lurking at the back of the seed box.

Each type was sown in a 6-inch pot on January 8^th this year, using a mix of multipurpose and seed and cutting compost. The seeds were sprinkled over the top of the compost and covered very very lightly with more seed and cutting compost. The pots were all placed in an unheated propagator and set under a north-facing skylight window to germinate.

Each of the pots had seeds germinating after 5-7 days. They were then taken out of the propagator and placed on a sunny south-facing windowsill, watered regularly and turned each day so that all the seedlings didn’t lean too much into the light.

Six weeks later, and they are at that lovely tasty stage just past microleaf. Big enough to handle, but still beautifully tender and fresh-tasting. We’ve had a light salad of raw peas, feta cheese and the leaves and green salads dressed very simply with a smidgeon of balsamic vinegar. The leaves are still too delicate, I think, to be soaked in oil.

  

 

Winter Blend (left) contains Kale Scarlet and Blue Curled, Mustard Red Frills, Rocket Dentellata, and Mizuna.

Speedy Mix (right) contains Salad Rocket Victoria, Greek Cress, Mizuna, Mustard Green & Red Frills, and Pak Choi Canton White and so is a bit of a cross-cultural mix with mainly oriental style leaves.

According to the packet Marshalls’ Finest Mix (centre) contains rocket, spinach, lamb's lettuce, red and green lettuce and leaf beet, but even on the closest inspection I can only find one or two spinach seedlings – everything else in my pot is leaf beet.

Speedy Mix is heavy on the feathery leaves and the Winter Blend is more substantial, especially when some of the leaf beet from the Marshall Finest Mix is added. These cut and come again salad pots can be sown throughout the year although I do find that in high summer they are prone to bolting.

Enjoyable though these salads are, I’ll probably never look quite so ecstatic while eating them as these women.