With most of the crops in our Kitchen Garden there is always a pressure for earlier harvests. True there is also the necessity to give a succession of crops, and a decent yield in total. But ask most people which crop they look forward to most and it is nearly always the first or earliest strawberries,, cherries, tomatoes, new potatoes and so on........
Of course economically it makes sense as with earlier crops you invariably get higher prices. That is in the sense of earlier in the season for that crop; which in Northern temperate zones usually means earlier in the calendrial year as well. However with plants 'early' can also mean 'quick' so that 'early' potatoes come to maturity and harvest much quicker than 'main crop' potatoes, and 'second earlies' come in between. And so you can start 'early' potatoes quite late in the year if you want to get a (late) crop as they can yield in the short time remaining which may not be long enough for a 'main' crop to crop.
There are further benefits from earlier crops; the first is that getting to harvest earlier in the year may free up the space in time for another or different crop to replace the first. And finally and much more importantly, they are giving us fresh vitamins earlier each year after we have probably been eating mostly stored foods for many months all winter and into spring. (To say nothing of the competitive spirit that places undue value on beating one's peers rather than concentrating on enhancing one's table.)
Of course it gets progressively harder to get crops earlier and earlier. It is easy for the amateur in the UK to have ripe tomatoes in July, harder by June, difficult by May and damn near impossible in April without an inordinate expenditure on heat. So although it may be possible to have almost any crop almost as soon as you want the effort and cost involved will become untenable, but don't let me stop you. The earlier you try to start the more difficult it is, and although the young seedlings do well initially that is because they are running on stored fuel which soon runs out and then they stagnate. The difficulty is the cold combined with low light levels as then things do not prosper. From late autumn till early spring the sun is low, dim and absent for longer than it appears, the plants simply can't grow strongly as they do not get enough energy and they are then subject to moulds and rots. Even if the top seems to escape the roots may be attacked resulting in wilting and death. None the less if we do not push too hard then each year we can grow most things a bit sooner than we do already.
Indeed whatever you are growing already, by whatever method, almost certainly will take less time to mature than it did a few years ago. Constant commercial pressure has bred earlier and earlier varieties of crops, especially some such as peas and sweet corn, reducing their time to harvest by weeks. This improvement continues and if you are growing only heritage seeds or do not try new varieties very often then you may be surprised when a new sort eventually reaches you.
Also the improvement may not be so much as in how many days the new plant variety can crop given perfect conditions but how quickly it does crop in less adequate conditions. For example the new all female small fruited disease resistant indoor cucumbers are not actually much quicker than the traditional sorts given commercial treatment but they do also crop incredibly easily and reliably given the very amateur conditions obtainable earlier in the year when the older ones would fail. The moral here is read all the catalogues carefully and try new varieties. There may also be alternatives, rather than trying to grow an early, or even an over-wintering, crop of lettuces which are prone to several complaints discover a taste for Lamb's lettuce or Miner's lettuce which thrive in the depths of winter. If you want early turnips then maybe some of the various forms of radish may serve as well and more quickly. Likewise many of the Chinese brassicas are much faster to mature than 'equivalent' Western ones, and for growing under cover they're invaluable.
The most usual approach for a slightly earlier crop is to start earlier; but as I pointed out above this gets progressively harder the earlier you try, even if you improve your methods and say go onto raised beds. Certainly in the open unprotected ground it is foolish to sow too early! Very rarely do the earliest sowings do half as well as those sown weeks later and not often do they crop that much earlier either. If you don't believe me sow a row of peas in only short sections at any time, a week apart, over a couple of months and see the difference. However give their ground a cloche to warm it up before sowing and keep the worst of the weather off and you can successfully sow and crop many weeks earlier than an unprotected sowing.
Indeed as we all know more protection, more heat, more light are all necessary to get the earliest crops. With the outdoor crops the best effort is to effectively bring them indoors; be it with plastic bottles, cloches or coldframes. To actually grow indoors enables us to provide heat and even more light artificially. Although these are possible outdoors, as with a hotbed or soil warming cable and outdoor lights, the expense is wasted unless the plants are also given weather protection with glass or plastic as well.
Outdoors the economics forces us back on improving the micro-climate (which I will be dealing with in a future issue) and then almost inevitably to putting the crops under cover. An exception is using soil darkening agents such as soot, or black plastic, to warm the soil, but again these would probably be more value still if combined with a clear plastic cover! Even under a cloche I can't plant out seed potatoes but I'm already eating ones grown in pots in the heated polytunnel. New potatoes can be had from pot grown plants in the warm year round; though the yields are poor and the plants miffy they taste grand.
For home consumption it's likely that a walk in greenhouse or poly-tunnel will provide more use year round than a series of temporary low covers which do not keep warm half as well. A load of big cloches are poorer still as they have too many gaps but they are of course movable and make crop rotation easier. A sufficiency of small cloches are essential for planting out earlier crops and particularly for the tender summer vegetables. Cloches can also be used within coldframes and polytunnels or greenhouses to give an additional level of protection, but the light is then very much reduced. Indeed this is always the difficulty with the earliest crops; the more protection you give them against the fierce weather and cold the more you reduce the already dim sun light. In fact under walk in cover of glass or plastic I reckon it is cheaper to increase the layers of insulation in winter to reduce the expensive heat loss and to substitute artificial light for the increasing dimness. Particularly as a proper growing light gives off a lot of heat anyway.
The use of extra light to give the plants a boost each day can be used in several ways. You can merely have it on for a short time, say from eleven till three; this will make them happier and stronger. If you give them more they will be more happy. But better still is to extend the day-length beyond the short winter's day of eight hours to a summery eleven or twelve per day. Most crops can be made to respond even more by a carefully programmed increasing, or lessening, of the day length, and even by extra short bursts in the middle of the night but that's another story.
Unfortunately although extra light is relatively cheap to run the equipment itself can be very costly initially as for safety it has to be specially constructed to work in the humid atmosphere under cover. But without doubt it is the way to most improve your success with the earliest crops. Just adding heat though can be counter-productive; without extra light the plants get drawn and leggy and it may be best to keep them cooler. Indeed even with extra light it's probably always best to have plants just a little warmer than their barest minimum rather than much warmer.
Extra heat is essential though for all the earliest crops; be it electric, gas or hot water radiators from the house system, all must be able to maintain the plant's minimum temperature on the coldest nights. If you have an inadequate heating capacity you risk losing all your early crops as the coldest nights nearly always come in February and March when many tender crops are well underway.
Heat underneath the roots is more efficient and promotes growth better than raising the air temperature. Modern soil warming cables are simpler than a hot bed. Though the latter is a much better device it takes careful management and cables are cheap to run and install. With the soil warmed most early crops will take much lower air temperatures than when standing in colder soil so the cost of heating the air can be reduced. This can be extended if the area warmed is given the additional subdivision of it's own cloche or coldframe. But once again we are back to low light.
Even position can affect the light levels considerably; we all know in the Northern hemisphere we need give the plants a southerly aspect facing the sun to catch the few rays of winter. We tend to forget that the sun is also low and so objects cast shadows that are not in the way in summer and thus the elevation becomes important. Invariably there is much more light on the staging than down on the ground in the border. This makes a big difference to plants and increasing the height of the staging or fitting shelves can improve their light no end.
Raised plants are also in warmer air, it may be many degrees warmer up near the roof. This can be a problem if there's insufficient ventilation as one fine day the sun may make them too hot. Cooking is a very big risk for all early crops under cover. Early crops especially strawberries do exceptionally well in pots on open shelving high up in the roof where the hanging fruits have few moulds and are free of slug damage.
For most early indoor crops the staging is usually the optimum place. It's considerably brighter and warmer than down on the floor and it is counterproductive to put early crops into the ground if they can still be accommodated higher up. A hot bed is a wonderful aid, self heated and raised, but requires a book of management in itself. Many plants can be grown in compost on top of a hot bed but still do not crop as early as the same plants confined there in pots.
Early crops should never be over- fed; they want only just enough to keep them growing. Other than some leaf crops there must be no lushness or the harvest will come late, and they'll be overwhelmed by disease and pests. In general the less you feed the better, as in cold soils when the plants do not take up the feed it converts to free ammonia which sickens the roots and poisons plants. Over-watering can be as bad as over-feeding and the earliest crops invariably need to be kept no more than moist at the most!
Likewise if you over-pot early crops the unused compost out of reach of the roots can go stale and again the ammonia given off may kill the plant. Also many plants such as tomatoes and peppers need to be kept confined in smallish pots to induce earlier flowering (effectively bolting) and fruiting. Continually re-pot and you'll wait longer for your harvest!
Even if you well light and don't over-heat, over-feed, over-pot or over-water your early plants under cover they will probably still not grow well because of a lack of carbon dioxide. In a closed space all this vital gas is rapidly used up. Without carbon dioxide the plants can't grow and although they can get some carbon from the soil they cannot prosper. A tightly shut up greenhouse or coldframe has little decaying compost full of animal life and there is no change of air. The answer is to provide the essential gas with bottles of fermenting sugary water and yeast. These can double as home brewing or slug traps depending on your whim!
This is even more important if you have a lot of big perennials as these will need a lot of carbon dioxide. Pot grown peaches, cherries, apricots are all extremely good for forcing early crops but do need good management to hold a heavy early crop. They need to be brought in in mid-winter and then crop before the outdoor ones have finished flowering. Grapes and figs are also easy to have months earlier than usual if they are brought indoors in late winter after being outside since summer.
With the greenhouse plants such as tomatoes, peppers and melons then stopping and disbudding to direct the growth into the earliest fruits can bring the first to ripen forwards by a month or more. For example if you remove the top of a tomato plant one leaf above the first flower truss you will be surprised how quickly the fruits set and swell. Furthermore a replacement leader will grow from below so the plant can be planted out later as normal anyway.
With tomatoes the disbudded tops and sideshoots can be potted up to root as new plants which being biologically mature flower and fruit much sooner than similar sized seedlings would. Cucumbers do not want stopping but melons do, either can be rooted, best by layering, for new mature plants. Peppers can be rooted from cuttings but do not then perform very well. However peppers are perennial and over-wintered plants will ripen fruits weeks ahead of those sown afresh.
To ripen quickly many of the greenhouse fruits require more warmth than is available, especially for the earliest crops. Luckily some such as tomatoes can be hastened by the ethylene gas given off by ripe bananas left with them. These also help bring pineapples into flower earlier! Unfortunately there is also a tendency in many plants for a ripening fruit to suppress other flowers on the plant setting or other fruits swelling. Thus it is better for production to remove maturing fruits as soon as possible. Some of these can be ripened off the plant with a ripe banana in a bag in the warm. But from the gourmet's point of view this is horrendous. So grow several lots of plants; for speed, quality and for sheer production if you need it.