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Starting from seed

assorted seeds

Seed Details

With a few exceptions most vegetables are annuals or biennials – or are treated as such – and are started from seed. Contrary to their inert look, seeds are living organisms that exist in a dehydrated state of suspended animation. Each one has an embryo and enough stored food to get it through germination – all it needs is air, sufficient water and the right temperature to germinate.

Getting things started

Ideally, seeds should be sown onto a moist, well-structured soil or propagating compost made up of fine particles, and then covered with more soil or compost. When wetted the seeds will take in water and swell up. Using the stored food, the embryos then develop both roots that stretch downwards and shoots that push upwards to the surface. By the time the shoots emerge the seeds have evolved into seedlings ready to grow on their own.

germinating cucumber

By the time the shoots emerge the seeds have evolved into seedlings ready to grow on their own: A cucumber seedling just emerging from the compost.

Buried alive

If seed is sown too deeply, the seedlings run out of food before they surface, suffering an untimely subterranean death. Because large seeds have more food reserves than small ones, they can be sown deeper in the soil or compost. As a comparison, the large seeds of beans can be buried 50mm deep, while the more diminutive carrot and lettuce seeds cannot survive depths of more than 20mm.

tomato seed broad bean seeds

Large seed has more food reserves than small seed and so can be sown deeper: tomato seed (left) and broad bean seeds (right).

Putting on the heat

Crops respond differently to their surroundings, and each one has an optimum temperature germination. Onions and leeks, for example, are at their best from 7 to 21 degrees C, while cabbages, peas and broad beans will germinate between 6 and a remarkable 32 degrees C.

Some crops are especially sensitive to low temperatures and need extra warmth for successful for germination. Tomatoes and sweet corn, for example, require temperatures above 10 to 12 degrees C. Despite their high standards, though, they are not as demanding as peppers, which must have temperatures of at least 15 degrees C to germinate.

Seeds sown when the temperatures are too cold will not germinate and may rot. To avoid crop failures, sowing should be done only when the soil or compost is warm enough to stimulate germination. Temperatures can be monitored with a soil thermometer, taking some of the guess work out of sowing.

seeds in a propagator measuring the soil temperature
Some crops, like peppers, require extra heat; measuring the temperature of the soil before sowing seed.

Numbers game

A garden’s success depends on seeds that are able to produce uniform stands of healthy plants. Only the best quality seeds will deliver this, and it is a false economy to buy anything second-rate, however cheap it might be.

One measure of seed quality is the percentage of seeds that germinate under the right conditions. No matter how good the seed is, however, germination is unlikely to reach 100%. This fact is reflected in the EU minimum requirements for vegetables, which range from 65% for carrot and leek seed, to 80% for cucumber and runner beans. Usually, however, the germination of seeds coming from a reputable company exceeds the legal minimum.

Like all living things, seeds are not immortal, and they start to age as soon as they are harvested. Though seed quality will stay high for a period of time after harvest, it will eventually start to deteriorate, ultimately ending in the death of the seed. Heat and humidity hasten the demise, while cool, dry surroundings will increase the life expectancy.

Proper storage under the right conditions will significantly increase seed longevity. To store seed all that is needed is a plastic food storage box or similar air tight container. The seed should be packed into the container with silica gel, a drying agent that absorbs moisture from the air. The container is then sealed up and put where the year-round temperature is maintained at 10 degrees C or less, which for most gardeners will probably be the refrigerator. The system is cheap and effective, though the silica gel, available from photography shops and web-based companies, must be periodically dried out – by heating in a low oven or on a radiator.

 

Starting Plants Off

Direct Seeding

‘Direct seeding’ is the term used when crops are established from seed sown directly into their final growing places. It means that after the seeds germinate, the seedlings are left where they are so that they mature into full-sized plants.

 

 

There are several ways to do direct seed vegetables . Narrow troughs called ‘drills’ can be drawn in the soil, and a single line of seeds dropped into each one. If wider troughs are made, then the seeds of closely space crops such as coriander and radish can be spread evenly as bands in the bottoms. Alternatively, large-seeded vegetables like peas and sweet corn can be sown singly into holes poked in the ground. Gardeners who grow large plots of vegetables may wish to consider buying a specialised push sower to facilitate direct sowing.

making a trough for sowing into
Making a drill to direct seed.
direct seeding direct seeding broad beans
Direct seeding radish seedlings (left) and broad beans (right).

Good quality seed sown in perect conditions will produce a good stand of seedlings. But if the weather is too dry or too wet, or if there is an invasion of slugs, the numbers of seedlings that emerge might be so small that vegetable yields are reduced. So when direct seeding, it is better to sow more seed than might seem necessary, thinning out seedling to the right population if too many emerge. Seed, even expensive seed, is cheaper than a lost opportunity.

crowded seedlings thinning seedlings
Row of Chinese cabbage overcrowded seedlings (left); seedlings being thinned out (right).

Producing transplants

Transplanting is the practice of moving plants from one place to another. In the case of vegetables, seeds are sown in one place, where they germinate and develop into young plants. Once big enough the plants are removed and transplanted to the spot where they will mature.

The advantages can be summarised as follows:

• Getting a jump on pests and weeds.

• Caring for small and expensive seeds that might otherwise get lost in the garden soil • Timely sowing of cold tolerant crops in wet springs

• Getting a head start on warm season crops like tomatoes and cucumbers

Along with its benefits, transplanting also has its limits. It may, for example, be too labour-intensive to transplant closely-spaced crops like coriander, while the long-rooted carrots and parsnips tend to fork if they are transplanted.

Ready-grown transplants can be bought from garden centres and nurseries, but gardeners striving for self-sufficiency may prefer to grow their own. A number of techniques have been devised over the years, and there is enough choice to suit most needs.

Compost-based methods

One method of transplant production is based on the use of bought-in propagating composts that encourage seed germination and seedling growth. Not to be confused with garden compost, the commercial composts used for propagation are spiked with nutrients and adjusted for pH, while being well-structured, well-aerated and well-drained. They should also be free from pests, diseases and weed seeds, though weeds particularly can sometimes be a problem.

The most popular brands of compost for vegetable gardening are made either from peat or coir fibre taken from coconut husks. Both, however, come burdened with issues of sustainability (the peat is mined from bogs, while coir fibre is shipped from India and Sri Lanka) and more environmentally-concerned gardeners might wish to look for alternatives.

One possibility is composted green waste that is produced specifically for propagation. There are several brands on the market but they should be tested before being adopted on a large scale.

Ambitious gardeners with small areas can try making their own propagating composts from ingredients such as worm compost, leaf mould and comfrey. Various innovative individuals and gardening organisations have devised their own recipes, and it is probably better to try these before making up something new.

Module living

A relatively new method of transplant production uses specially-designed seed trays called modules. The modules are divided into individual cells that are filled with compost. Seeds are sown into the cells, and the trays kept either in a heated propagator or unheated structure like a greenhouse: the final site depends on the crop, time of the year and whim of the gardener.

lettuces in modules 
Lettuce transplants raised in modules.

The normal goal is to grow only one seedling per cell. Some crops, however, can be multi-seeded and grown at higher populations. The extent of the population increase depends on the crop, and varies from 3 to 4 seedlings per cell for turnips, 5 to 6 for bulbing onions and 7 to 8 for salad onions. The seedlings from a single cell are transplanted together as a group without being separated. The planting distance left between the groups should be greater than it is for single plants.

Once the roots fill the cells, the seedlings with their compost need to be taken out of the trays and relocated to the garden soil. Crops destined for tunnels or greenhouses can go directly to their final resting place. Those going outside, however, should be kept in their trays and moved to the cooler outdoors to be hardened off before transplanting. This move is supposed to toughen up the seedlings and prepare them for a less-pampered life in the open air.

mizuna module
Plants raised in modules are ready for transplanting when their roots have filled the cell.
using toilet rolls  using toilet rolls as a module
If you don't have a module tray for raising transplants toilet rolls can be used.

Pottering about

Warm season crops like peppers, tomatoes and aubergines respond to heat at every stage of growth. Started in February or March, their seeds can be scattered in compost-filled trays and put into heated propagators to stimulate germination.

After the seeds germinate, the seedlings are gently teased out of the trays – in a time-honoured practice called ‘pricking out’ – and transplanted into small pots filled with compost. The heating should be continued, and the pots either kept in the propagator or moved into a mini-tent constructed inside a tunnel or greenhouse. A mini-tent is inexpensive to make from plastic sheets or film, and can be fitted out with a heater that is turned on whenever the temperatures drop. Because it is small, the tent is quite cheap to heat.

Around April or May, when the pots have been infiltrated with enough roots to hold the compost together, the young plants can be transplanted to their final growing place which can be a large pot, grow bag or soil in the greenhouse or tunnel. With warmth and sunshine, harvesting should begin sometime in July or August.

sowing tomato seed into a tray pricking out tomatoes
Sowing tomato seeds (left); pricking out tomato seedlings (right).

Bare-rooted transplants

With bare-rooted transplanting, seeds are sown directly into the garden soil – either outdoors or under cover – where the seedlings grow until they are lifted and transplanted elsewhere. Unlike compost-based propagation, this technique requires no special equipment, though the seedlings have to put up with competition from weeds and the unwanted attention of slugs at all stages of their development.

Growing bare-rooted transplants is generally restricted to leeks and brassicas like kale, sprouts, and cabbage. Seedlings are closely spaced in rows 25cm apart, and are ready for transplanting when the brassicas are about 15 cm tall and the leeks as thick as a pencil. After watering the day before, the soil is loosened with a fork and the seedlings are gently pried out of the ground with as little damage to the roots as possible.

Handling transplants

Moving seedlings from one site to another is likely be a traumatic experience for the young plants, especially if they are bare-rooted. The seedlings’ roots must be treated gently, and the tradition of firming transplants into the soil to ensure good soil contact is not recommended. Instead, a thorough watering immediately after transplanting will achieve a good root-to-soil contact without doing any damage. Establishment of seedlings is facilitated by transplanting into a well-worked soil on a dull day, followed by light, frequent waterings.

 

Young bright light seedlings mature bright ligts
When Chard var. Bright lights is multisown in modules, the clumps have mixed colours! Young plants just transplanted (left); the same bed with mature plants of bright lights.

 

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