All sweet peas varieties are annuals. They are easily raised from seed, and are considered one of the easiest of all seed plants to grow in the garden. The viability of seeds is good and the grown plants are large and easy to handle. In fact, every seed bought may well turn out to be viable and will grow into a healthy plant, provided it is given sufficient moisture and warmth. Sweet pea seeds will germinate quite readily and grow without a lot of fuss and preparation of soil.
One of the most adaptable garden plants known, the sweet pea is very easy to grow. The original wild flower, Lathyrus odoratus and the other related annual species behave as winter annuals under natural conditions. Sweet pea seeds will germinate in the fall, and a cool moist winter will encourage slow top growth, however, the development of the roots is greatest at this time - these will reach and grow down towards the subsoil layer. As spring approaches and the day light hours increases and intensifies along with a rise in temperature, there is increased growth of the shoot and leaves are given off in preparation for a floral bloom. At the same time, the rate of root growth is also accelerated and starting from an established root system. The roots begin to go deeper in search of moisture reserves in the soil as rainfall decreases to almost nothing and the heat of the sun begins to increase the rate of evaporation and moisture loss from the leaves of the plant.
The plants will bloom fully during the spring with the seeds ripening in the dry air of the summer season. Once the pods borne on the stems dry up, they split and twist with a snap and fling out the seeds on the ground. The presence of the hardened seed coat protects the seeds from drying out in the full heat of the summer. Germination can begin with the arrival of autumn rains, with the seed coat softening in the moisture from the rainfall.
The early development of the roots in garden sowed plants is promoted by sowing the seeds in the autumn season. This planned timing will result in plants that flower early, have a longer flowering period, produce longer floral stems and bear more flowers on a stem along with larger flowers on the stems. Such plants will usually be healthier as well and be far more productive in terms of flowers borne on the stem and quality of seeds. The reason for this is the increased flow of moisture and nutrients from the expansive root system that has the time to develop in such plants. This is the preferred approach of the majority of floral exhibitors, at the same time; most gardeners tend to leave off sowing until the arrival of the spring season. The approach of gardeners can work out quite, in places where the climate permits spring sowing, but on the whole, sowing seeds in the autumn may greatly help gardeners produce better plants with good flowers and other optimal growth characteristics.
The common method for autumn sowing is to sow seeds in prepared pots. Once they germinate, the young plants are over wintered in the pots, and then transplanted to the soil during the spring season. The time of planting for seeds sown in the autumn is also carried out around the same time that sowing is done in the spring. Thus, the plants sown in the former season have a clear head start in terms of growth over those sown in the latter. Where the climate is mild all year, it is quite possible to sow seeds directly outside in the open ground.
When sowing seeds in areas that are marked by very cold winters and by correspondingly hot summers, the practice of sowing seeds in the autumn either on the open ground or in pots will help ensure the flowering peaks before the arrival of excessive heat in high summer. This method of sowing seeds is also suited to places where the spring is short and serves simply as a brief period of transition from winter to summer. The protection of the seedlings from the full glare and ferocity of the winter is also essential so it is in such areas that growing sweet peas demands the most thoughtful consideration, and the maximum protection for pot grown seedlings is required in such places. The perfect place to grow plants in such areas may be a good sun room.
Sweet pea seeds can also be sown on the open ground in the spring season. This may be carried out in long rows for ease of cutting later. This method was at one time common and the preferred method, especially when seeds were cheap and easy to get. This method is also labor intensive and often required hired staff to help with the care and cultivation of the crop.
The sweet pea seeds available in the market are high quality seeds and are usually grown in a climate and in a manner that makes sure that their germination potential is good. Getting all the seeds to germinate is not a rare event. This may lead to the belief that all one needs to do is to sow seeds out in the garden and expect the plants to grow - however, this may not always be the case even if the viability is high. Optimal growth of seeds will still require the right conditions to exist and growth can depend on other factors, besides the viability of the seeds being sown.
Seeds that have been procured from professional gardening stores or seed houses are to be preferred over seeds that are saved at home. Enthusiasts and hobbyists may not take to this idea and it might even sound heretical to the floral amateur to whom saving their own seed from the garden is looked on as a right and an important safeguard against future losses. However, the seeds obtained from domestic gardens are usually from plants that have developed in an uncertain environment, especially if the place faces long cool and damp summers. Therefore, such seeds will not boast the high viability of seeds that have been grown by specialist seed growers and professional seed houses. Hobbyist and amateur gardeners growing plants in home gardens may miss unwanted variations in the color, the vigor or productivity of the seed producing plants. They may not be collecting seeds from among the best plants. Unwanted characteristics can reappear in plants grown from seeds produced by such rogues or off types. Such unwanted characteristics can become stronger in the progeny of plants grown from such seeds.
Therefore, it is advisable to source sweet pea seeds from sweet pea specialists or from reputed seed companies that have a good range of sweet peas in their inventory.
The presence of a hardened seed coat on the seeds of most varieties of sweet peas helps prevent the seed from drying out during the hot desiccating summer, especially, in places where sweet peas grow in the wild. Wild species of sweet pea also have another survival advantage due to the presence of this hard seed coat. The autumn rains may not soften all these hard coated seeds in the wild, though many will germinate after the rains, other seeds may not germinate at all, however, as the hard seed coat protects the seed from all natural elements in the intervening period - they stand a good chance of germinating after a further soaking the following year, or the year after that and eventually as time passes, all the seeds will germinate. The fact is those even though, the whole season's seeds will rarely germinate at the same time, but stands a good chance of germinating eventually. There are significant survival advantages of such seed coats in the wild, especially, if bad weather, insect damage or some other natural mishap happens to finish off all the current season's seedlings growing from seeds that germinated, the seeds left behind without germination in the soil will recoup the losses and produce a new generation of plants the following year or the year after and so on.
This fact should be contrasted with one other, that gardeners tend to want all their seeds germinating together. This not only makes for ease of handling and ensures that all the plants take up water and germinate in sync, it is very convenient when the seeds are being sown in pots. Germination of seeds is also aided by breaking through the hard seed coat to ensure that enough moisture penetrates the seed coat and reaches the seedling within.
This can be brought about by a number of different means:
The sweet pea seeds can be prepared for sowing by spreading them out onto a piece of sandpaper, a second sheet laid on the top and rubbed over the seeds will erode and wear out the seed coat in no time. All the seeds can be treated in this way and sown.
A large sized nail clipper is also employed by gardeners; this is used to nick the seed coat. This method has its limitations, as some seeds are easier to nick due to a slightly nobly surface or edge that can be conveniently clipped off, however, most sweet pea seeds are more or less round in shape - therefore, this technique may not always work.
One commonly used preparation technique involves soaking seeds. This is carried out by lining a small plastic box with moist kitchen paper and spreading the seeds on it. The lid is then placed and the box kept in a warm and well lighted place. To get the perfect soaking for seeds, the paper used must not be soggy but moist; the site chosen for keeping the box should be warm but not hot, the ideal range being 7-18°C or about 45-65°F.
Once they have been subjected to soaking, in a few hours, most of the seeds will swell up if not all of them. This is the sign that shows germination has begun and indicates the uptake of water by the seeds. The difference in seeds that took up water and those that haven't will be evident. Once this stage is reached, the seeds that have not swollen can be taken and treated further, by nicking the seed coat with a knife or file and keeping them on a damp sheet. This treatment will ensure that they swell up. Once seeds have swollen up, they are considered to be ready to germinate. Germination occurs soon after and the seeds can be left for a day or two for this to take place. The roots will soon emerge, this event occurs fastest under warm conditions, and the seeds should be sown immediately when they appear. The arrival of the seeds to this stage of growth is called "chitting," and many gardeners use this technique to ensure a good crop.
Many different approaches and alternative strategies can be followed when deciding location, or the type of pots and compost to be used in growing the sweet pea plants. These will in turn be dictated by the level of experience, the personal preference, and the facilities available to the grower.
The type of pots to be used in growing sweet pea plants is an important factor to consider. Sweet pea plants have been traditionally sown either in 12.5 cm or 5 inch clay pots and sometimes in individual open bottomed bitumized paper sweet pea pots - these types of containers are not utilized these days and are considered old fashioned. These days, the alternatives are to use plastic modules, large plastic pots, or small plastic pots - depending on the preference of the gardener.
Large pots can have certain advantages, one is easy availability of such pots, the other advantage is the relative ease with which a large mass of compost can be handled and kept suitably moist inside a large pot. The disturbance to the root system of individual plants is minimal when plants are planted out as a whole. However, when planted separately and the root ball broken up, some plants may suffer root damage. Only the gardening purist may be upset by this as the effect is so small and plants remain healthy.
The serious sweet pea enthusiast may prefer the use of plastic modules, rootrainers in particular; this is the successor to the old sweet pea pots - most professional gardeners prefer to use them. Each single tall and slender, re-usable module is used for a single seed. The advantage of the module is that it splits to permit growing plants to be removed easily for planting out; the module can then be washed and re-used many times. The modules allow a deeper root run, and this is a distinct advantage. The benefit of these modules also lies in the fact that they are part of a simple system in which the modules are suspended on a plastic frame so the base of the pots hangs free and unobstructed, allowing for maximum growth. This is called 'air-pruning' - an allusion to the fact that the roots start to emerge from the base of each module, and the exposure to the air causes growth to cease automatically and the roots to put out root branches higher up in soil inside the pot. This causes the development of a well branched root ball, which can develop a very strong root system when the plant is out planted in the soil.
A peat based seed compost or multipurpose compost or a peat-free alternative has been utilized by many growers to get excellent results. Gardeners and enthusiasts are advised to test soils when using peat free composts; it is always a good idea to run a small trial alongside using the usual compost before changing to the new formulation for growing the plants. This is because plants grow differently in peat-free composts than they do when grown on peat rich composts. This is particularly so, with respect to the requirement for water and nutrients, these composts cannot be managed in exactly the same manner as plants have different growth characteristics in different soils.
To get a good growth of plants, the compost must be kept moist, but not soggy at all times and repeated checking may be necessary. Composts must be filled to the rim of the pots, no matter what type is used; the pots will then have to be tapped on a table or bench to allow the compost to settle down in the pot. It is also a good idea to firm up the compost gently to remove any air pockets in the soil, the forceful use of the fingers to firm up the compost must be avoided as compacting the compost too much can dramatically reduce the drainage potential of the soil - this will affect plant growth. The simplest way to firm up soils when using round pots is to gently firm the compost down by tapping with the base of another pot.
The pots can be kept in a well ventilated cold greenhouse, in a cold frame with the lid slightly open, in a cool sun room, or in a sheltered place out of doors. The most important factor is to keep the compost from turning soggy due to excessive moisture retention. Drainage is necessary to avoid soggy composts, especially when sowing seeds in seed pots during the fall. When these are stood outside on a slab or on some other hard surface, they tend to become too wet if they are not raised up to a height to permit all the excess water to drain away from the soil. To allow for good drainage, it may be a good idea to improvise a gravel bed, which can be surrounded by bricks or timber to keep an inch of gravel in place beneath the pots. This gravel bed can be ideal for proper drainage when using smaller pots. There is another advantage of rootrainers, as these can be stood in their frame and have little problem with drainage.
For plants that have been sown in the fall inside greenhouses, the frames should be placed on gravel beds or stood on slatted bench and kept well ventilated at all times. If cared for properly, the plants will not be damaged by a light frost, however, precautionary measures must be taken if the weather is severe and all ventilators should be closed as protection against damage. A greenhouse with a good heater is a requirement for gardeners living in very cold regions, as a heater can help keep out the worst of the frost and prevent damage.
One more option is to sow in pots placed on the windowsill, this is especially ideal for dwarf varieties of sweet pea. When growing plants on a windowsill, the best approach is to employ Rootrainers or modules, or sets of pots in a series, each 2 inches or 5 cm square connected together to fit neatly into a seed tray for support on the windowsill. The direction of incipient light is the main problem encountered when growing plants on the windowsill as the light will come only from one direction. One way to slightly improve the situation is by turning the tray once every day but the tall climbing types of sweet pea are still apt to become too very thin and their roots too constricted due to poor lighting on one side. Therefore, in some cases, the quality of the plants will be below par.
When seeds are sown in spring on the other hand, the place where plants are grown must be kept cool at all times to avoid fluctuations in temperature. The growth of sweet peas may be impaired and plants can be thin and wispy if they are raised in a greenhouse alongside half-hardy annuals that need warm temperatures to grow properly. When sowing in the spring, the place where plants are growing must be well ventilated with no additional heat - this condition is crucial for ensuring the proper development of a strong root system. It is also necessary to avoid vigorous top growth by pruning the plants from time to time.
The emergence of a slender pointed shoot from the soil is the first sign that germination has occurred. This event will be followed by the appearance of simplified leaves that will unfurl along with side shoots that break towards the base of the plant near the soil. The development of the side shoots varies with the growing conditions and the variety of sweet pea plant grown. The usual practice is to encourage robust side shoots growth by pinching the main root from time to time, particularly because the main shoot tends to weaken and die off as the side shoots take over the task of maintaining the plant in the soil.
It is important to keep the pots in a moistened condition at all times. There is a danger of over watering the growing plants as excess of water can rot the seeds, seedlings and later the roots of the growing plant. At the same time, the reluctance on the part of the gardener to use too much water, must not prevent the pots from receiving a good soaking now and then; the aim is to follow a policy of cautious watering of the potted seedlings, in which only the top half of the compost in the pot is dampened - the problem is that such an action can stop the roots from putting the depth of the compost to maximum use in their search for water.
It is best to feed during these early stages of growth. This step is desirable particularly when the compost employed is standard commercial seed-sowing or multipurpose compost. A specialist sweet pea fertilizer or a liquid tomato feed may be used on the compost, but overuse must be avoided at all cost as it can affect the plants. Plants that were sown in the fall tend to grow slowly over a period of many months and one should not force them into untimely and vigorous growth but it may be better to ensure that the growing plants never go short of the nutrients they require for proper growth. Plant growers can use the nature of the season and the prevailing weather conditions as a guide for growing plants. Compost must be fed only if the conditions are naturally likely to promote good plant growth.
It is also beneficial to regularly feed plants sown in spring to help maintain consistently growth, once about every two weeks is ideal. At all times, gardeners must check that the compost is thoroughly soaked to ensure good growth of the growing plants.
Pinching of the seedlings of all types of sweet pea can be done when the growing seedlings are about 7.5cm (three inches tall.) The pinched plants will benefit and quickly develop side shoots; the dwarf and intermediate varieties need not be pinched, these shorter varieties can be left growing without being pinched.
The easiest way to pinch plants is by giving each stem a simple nip using the thumb and forefinger, the plant can be nipped off just above a leaf joint and left to grow on its own. Side shoots will begin to come out of the stem, two or three side shoots will usually come forth from the base and when these are about 7.5cm to 10cm (three to four inches high), and still self-supporting - they can be planted out. If these newly emergent side shoots are left longer on the stem, not only will the roots become restricted in growth but the shoots will tend to flop and require constant support. This will disrupt the process of strong and sturdy growth, often growth will occur in spurts rather than continuously as it should.
It is not vital or even necessary to sow seeds in pots, though sowing in pots does tend to produce the best plants - with good and sturdy physical characteristics. Good and even impressive plants can also be obtained from seeds sown directly into the garden soil, either in the fall or the spring season - the good growth of plants may also depend on the climatic regime in the area where the plants are being grown. As a rule of thumb, spring sowing is preferable in all areas except in places that have mild and equable winters. The type of soil on which the plants are grown may also influence their growth characteristics, sowing in the fall in the open garden on heavy clayey soil for example is likely to result in far less successful plant growth. Soils that are used for sweet pea should preferably be loose and crumbly in texture. This can be brought about by lightly forking over the area, working some organic matter like old potting compost, the contents of last season's growing bags, or a soil improver from the garden centre, into the soil can boost plant growth. The usual technique is to initially tread over the soil, then raking it level, with some fertilizer finally being raked into the soil.
Sites used for sowing the seeds should be placed fifteen to twenty three cm apart (six to nine inches apart along a row of netting, or even at the foot of individual canes to support a single plant.) The successful growth of the plants will also depend on the method of support employed to grow the plants. The biggest error is to sow seeds too closely together, although more plants will grow as a result, the seedlings undergo intense competition for resources and, this in the end becomes counter productive, as fewer surviving plants usually mean fewer flowers even if the plants are sturdy. Once seeds have been sown on the soil, the seeds can be covered lightly with soil then watered in thoroughly using the hose on the watering can. The use of liquid feed to the water is important when sowing chitted seed; this will ensure that plenty of dissolved nutrients are taken up by the new roots as soon as they appear. It is also important to protect the seeds and growing seedlings against attack by mice, slugs and pigeons. When new seedlings emerge, ensure they receive enough water to avoid them drying out before they are properly established in the soil.
This technique of managing seedlings came into prominence many decades ago as an occasional method of increasing stock of new varieties or to help produce more plants when a seeds sown germinated poorly against expectations. The technique involves pinching out growing seedlings in the usual way, with the resulting growth of young shoots being snipped off and then rooted in soil when they are approximately 7.5cm (three inches) in length. These seedlings can then be treated in the same way that spring cuttings of perennials are treated. It is best to root them in a 50:50 mix of peat and perlite in a propagator with heat at the bottom around 70°F (twenty one degrees centigrade.) Once handled in this way, the seedlings will give off roots in two to three weeks, and these can then be moved into pots and grown before being planted out in the soil. It is important to always leave at least one shoot growing on the original seedling so that it can develop properly. As the shoot tips from older plants will not root - older plants cannot be used in this technique.