If you’re new to gardening, or simply want to learn more about how to sow seeds, this beginner’s guide is for you. We’ll teach you the basics of sowing seeds, including choosing the right type of seed, how deep to plant them, choosing the right type of soil and when to water them.
When purchasing seeds online you may come across different abbreviations used in the descriptions. These are used to represent the characteristics of the seed. The following are common abbreviations you may encounter:
HA – Hardy Annual
These are flowers whose life cycle lasts just one year. If allowed to germinate, they will mature and bloom in the summer after being sown in the early spring. This group of flowers can be sown directly into their flowering positions in the garden and does not require indoor cultivation.
HHA – Half-hardy Annual
These also germinate, bloom, and then die in the same year, but they need more time to grow than hardy annuals. They are sown in trays in the early spring and placed in a warm, light location like a propagator, sunny windowsill, conservatory, or heated greenhouse to give them this early start.
Half-hardy plants are frost-tolerant and should not be planted outside in their flowering positions until all frost danger has passed. They are gradually hardened off in preparation for transplantation. This category contains the majority of popular summer bedding plants.
HB – Hardy Biennial
The young plants in this group are moved to their flowering position in autumn or early spring to flower approximately one year after the seed is sown.
HHP – Half-hardy Perennial
This group of flowers will flower in their first season if the seeds are sown early in the year in a heated greenhouse or propagator. This is true for the likes of Geranium and Gerberas, which are regarded as annuals that are only half-hardy and are discarded after flowering. However, geraniums can be removed before the first autumn frost and kept frost-free throughout the winter. In the latter part of autumn, Dahlias and other plants with tuberous roots should be lifted and stored.
HP – Hardy Perennial
This group includes the stunning border plants lupins and delphiniums, which continue to bloom year after year. Although it is possible to sow the seeds as with hardy biennials, many gardeners prefer to do so indoors in trays in March or April. When the young plants are large enough to handle, they are put in their flowering positions for the autumn of the same year.
Coping with small seeds
Handling tiny seeds can be challenging. There are times when the foil packet appears to contain nothing more than a trace of dust-sized particles. How to make the process of staking small seeds a little bit simpler is as follows.
For sowing, use a small pan or pot about 4 or 5 inches deep. Then, add seed compost to the point of overflowing the pan or pot. First, use your fingers to press it down, then use a wooden presser. Shake the seed packet to combine the sand and seed after adding a heaping teaspoon of silver sand.
To evenly distribute the sand-seed mixture over the compost, directly sow the seed from the packet by tapping it slowly. Use the wooden presser to simply press the seeds into the surface rather than covering them with compost. Standing the tray or pot in a bowl of tepid water will allow you to water the compost from underneath. Cover the compost with a piece of glass, cling film, or a polythene bag to keep it moist and the air a little humid. Keep in mind that the germination rate of very fine seeds is lower than that of normal-sized seeds, and the right temperature for germination is very important.
Damping Off Disease
One of the most prevalent and troublesome forms of the garden disease is damping off. It can affect any kind of seedling, but it’s most troublesome for flower seedlings that are growing quickly. Some slow-growing trees and shrubs are also particularly susceptible to damping off in the form of grey mould.
Seedling death is the result of all symptoms. Young seedlings frequently shrivel up into small, roughly circular patches, appear weak and have shrivelled stems, or the root system simply rots away. Leaf spotting or other discolouration, as well as grey mould on the stems or leaves, occasionally appears on larger seedlings or young plants.
There are a variety of organisms that cause damping off symptoms. The fungi Pythium and Rhizoctonia solani, which persist as spores in the soil, are the ones that most frequently result in patches dying out. Alternaria species that live in the soil frequently cause stem lesions, and Phyllosticta and Pseudomonas fungi that live in the soil typically are responsible for leaf spots. Botrytis cinerea is responsible for the grey mould that frequently develops after damping off.
The garden environment makes treatment difficult. Chemical controls have been used in business, but they aren’t yet available for small-scale use. Hygiene is essential for amateur or small-scale growers at all propagation stages. Use only pots and seed trays that have been cleaned and disinfected, and ensure that greenhouse benches are clean. Additionally, you should use proprietary sterilised seed compost and the mains water that is moist but not excessively so. The majority of purchased compost is not sterile, so don’t assume it is.
By “cooking” small amounts of compost for seed sowing in an oven at 150 degrees Celsius for about an hour, it can be sterilised. When using water that isn’t from the tap, be careful. When treating susceptible plants, tap water should always be used first. All storage tanks should be cleaned and disinfected regularly.
By avoiding waterlogging and high humidity, which will make plants and seedlings more susceptible to attack, stress should be avoided. Seeds should be thinly sown and pricked out as soon as possible, with the stems and leaves of the seedlings being handled. Remove all affected seedlings, a few additional seedlings, and the affected compost if only a portion of the seed tray has shown symptoms. Do not reuse affected compost. To help stop the spread, water with a fungicide like Cheshunt Compound. As a preventative measure, Cheshunt Compound can also be applied to the soil before sowing seeds, but this will not eliminate all issues. It ought to be utilised as a tool for prevention.
There may be a mention of “pre-chilling” in some instructions. Seeds that would otherwise take a long time to germinate often benefit from this pre-treatment, which speeds up the germination process. However, you should never throw away a seed container too quickly because some seeds may continue to refuse to germinate even after being pre-chilled for at least a year.
Traditionally, the pots were pre-chilled by being placed outside in a cold frame during the winter. If you get your seed outside of the winter, the following method is especially useful because it is frequently quicker to use a domestic refrigerator.
Sow the seed in moistened seed compost, place it in a polythene bag, and leave it at 15-18 degrees Celsius for three days before putting it in the refrigerator for the recommended time. Large seeds can be mixed with damp seed compost that is two to three times their volume and put directly into a polythene bag that is sealed and kept in the refrigerator for convenience. However, the compost should never become excessively dry or wet, and there should always be enough air in the bag. These seeds can be firmed up by spreading them on top of a seed container with compost after being pre-chilled.
While pre-chilled, the seeds must be moist, but if they are actually in the water, it will be harmful. If any of the seeds begin to germinate while they are in the refrigerator, check on them once a week and move them all into the appropriate warm conditions.
After pre-chilling, it also appears that light is beneficial; therefore, pre-chilled seeds should only have the lightest covering of compost, if any, and the seed trays or pots should be exposed to light and not covered in paper.
In two ways, soaking is beneficial: It can soften a tough seed coat and remove any chemical inhibitors from the seed that might prevent germination. In most cases, one to three hours in water that is initially hot is sufficient. If the soak is prolonged, the water should be changed every day. Some species’ seeds expand when they are wet. The remaining seeds should be gently pricked with a pin and returned to soak in some of the batch’s seeds swell within 24 hours. Before each seed has time to dry out, it should be removed as it swells and sows.
Pricking out seedlings
When seeds germinate, the cotyledons, or seed leaves, are the first leaves to appear. Most of the time, these are two oval, fleshy leaves that look nothing like the mature leaves of the plant. Seedlings should not be transplanted or pricked out until the first true leaves appear, but gardeners should use common sense and only move them when they are large enough to handle.
This could be before the true leaves have developed in the case of large seedlings; therefore, it is recommended to sow these plants separately in small pots.
It can be tricky to transfer tiny seedlings from the sowing container into trays filled with good universal compost. Never handle plants by their stems, which are prone to bruising, but always by their seed leaves, as this is the golden rule. To gently remove the seedlings without damaging their delicate roots, some people use a metal tool known as a widger or a sharpened or tapered piece of wood like an ice lolly stick.
Some seedlings will have to be sacrificed, given to friends, or put in the compost bin because there will always be more seedlings to transplant than trays can hold. Giving the transplanted seedlings enough space to grow into sturdy young plants is crucial. Allow approximately fifty seedlings for each full-size tray as a rough guide.
Before actually removing the seedlings from the sowing container, it is wise to prepare the planting holes in the trays of moistened compost. Simply position each seedling so that the roots fit neatly into the hole. Then, while still holding the seed leaf, gently press the compost into contact with the baby plant.
The pricked-out seedlings will get a good start in life with enough plant food in proprietary composts, but you can start feeding them with a diluted liquid fertiliser after about two weeks if you want.
Hardening off seedlings
Because they would be damaged by frost, strong winds, or cool growing conditions, half-hardy annuals, half-hardy perennials, and some vegetable seeds must be germinated indoors.
At the beginning of the year, they are sown in a warm room, propagator, greenhouse, or even the airing cupboard. The majority of seeds require a minimum temperature of 18C and can withstand overnight temperatures as low as 10C, with a few exceptions that are discussed separately.
The seedlings must receive ample light, but not direct sunlight, once they emerge until they are large enough to be pricked into trays.
The young plants are hardened off as the final step before being planted out. The idea is to gradually get the seedlings used to the more challenging environments of the great outdoors. Do this for at least ten days, preferably longer.
To begin, lower the temperature in the greenhouse or propagator for the remainder of the day and place the trays outdoors for two hours during daylight. Increase the amount of time the plants spend outside slowly so that, by the time the frosts are over, they are used to being outside. Remember that the trays need to be watered and protected from heavy rain.
It’s possible that even after the young plants have been moved to their flowering spots, they will still require some form of protection from the damaging effects of strong, cold winds.
A cold frame is an extremely helpful tool for successfully hardening off. It ought to be big enough to hold all of the seed trays, but it can be a simple, cheap structure. The lights, which are the plastic or glass cover over the frame’s walls, can be opened or taken out completely during the day; however, they must be put back in place overnight.