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When to sow what seeds for seedlings? A guide for beginners

“When to preplant seedlings?”, “When is the best time to sow tomatoes and peppers?”, “When to put the seedlings outdoors?” – These questions are asked by every amateur gardener since January. In this article we explain when to sow what seeds, because properly grown seedlings are the key to a good harvest in the vegetable patch or a lush flowering in the garden.

Sowing seeds and preplanting: The growing cycle begins on the windowsill

sow seeds and grow seedlings on the windowsill

The number of warm days in our latitudes is pathetically low for the full vegetative cycle of any plant species. Therefore, we begin this cycle on the windowsill (by preplanting seedlings), rather than planting seeds directly in the garden soil. If the light there is insufficient, you can use artificial light sources. Plant lights, still called phytolamps, are perfectly suitable for this purpose.

The duration of the growing season depends on the rate of maturation of the variety. This varies not only between species, but also between varieties. For example, there are specially bred early-maturing varieties for growing in the conditions of a short northern summer (but those who are impatiently waiting for the first tomatoes, will also be delighted).

However, there are still plants that have a very long growing season, such as chabaud carnation (Dianthus caryophyllus var. schabaud), busy lily (Impatiens walleriana), lobelia (Lobelia), garden strawberry (Fragaria ananassa) and others. For them, you need to apply additional lighting, artificially increasing the light day to 15-16 hours.

sowing seeds correctly take into account the recommended depth

So when should you sow the seeds? And when should the young plants go out? The best time for sowing seeds varies depending on the stage of plant development. It is important to know how many days it will take for the seedlings to sprout, if and when they need to be harvested, and the recommended age for planting the seedlings. This information, as well as the total duration of the growing season, is usually listed on the seed bag – for the particular variety. So far, everything is clear, but what to do if this is your first gardening season? You have never sown tomatoes, and you do not know anything about their germination period and sowing? For your region, May 15 is early spring, but wouldn’t it already be too “late” for sowing ? Try to count the first year strictly by the calendar.

When to sow what seeds ?

When to sow what seeds

The average dates for the most popular vegetable crops are as follows:

(germination period / age of seedlings for sowing in the open ground).
Cucumber – 2-3 days; 25-30 days;
Tomato – 6-8 days; 45-60 days;
Bell bell pepper – 12-14 days; 65-75 days;
Eggplant – 10-12 days; 50-60 days;
Zucchini – 3-5 days; 25-30 days;
Squash – 3-5 days; 25-30 days;
Lettuce – 3-5 days; 35-45 days;
Celeriac – 12-18 days; 75-85 days;
Leeks – 12-15 days; 45-55 days;
White cabbage – 4-6 days; 40-50 days.

To determine when seedlings should be advanced, count from the expected date of planting in the ground: 80 days for peppers means sowing seeds in February, 60 for tomatoes = mid-March, 50 for cabbage = late March, and so on.

It is not also not a problem to be late

As spring approaches, the daylight hours are longer, which means seedlings get more natural light. It has long been observed that tomato and bell pepper seedlings planted later easily catch up and then overtake those sown earlier.

The age of seedlings is the most important factor for outdoor sowing. And it is better to plant seedlings slightly undergrown than overgrown. Overgrown seedlings are more difficult to transplant, root much worse and are more susceptible to disease during the adaptation process. This is one of the reasons why the timing of sowing for seedlings should be calculated individually.

What is the climate in your region?

growing seedlings from seeds on the windowsill

The time when seedlings can be planted in a permanent place depends on the climatic conditions in your region. Look for a period of consistently warm temperatures without renewed frost. Therefore, for any gardener it is important to know the number of warm days in the month. It is clear that they can change from year to year, but here we can only rely on weather forecasts, the accuracy of which, unfortunately, leaves much to be desired. Therefore, for sowing can first be guided by average values, which are based on long-term meteorological observations.

Where to plant seedlings?

growing seedlings in a greenhouse

There is a difference whether seedlings are planted outdoors, in a plastic tunnel, in a polycarbonate or glass greenhouse. The timing of planting seedlings and sowing seeds in the open ground and in the greenhouse usually differs by 30-45 days. The higher the bed, the earlier it warms up. Planting in raised beds can be 2-3 weeks earlier than in the open ground at ground level. As it turns out, peppers for seedlings in the greenhouse can be planted as early as January.

Outdoor sowing of cold-resistant and slow-germinating plants (radishes, lettuce, carrots, parsley, dill, radish, cabbage, turnips) begins when the soil at a depth of 5-10 cm warms up to 8-10 degrees during the day. At the same time, the first seedlings of heat-loving plants such as peppers, tomatoes and cucumbers can be germinated in the greenhouse. Since most of Germany is in the cool temperate zone, this means roughly in the period between May 1 and 10. For the southern regions, early April to mid-March.

Tomatoes and seedlings of other heat-loving plants should be planted outdoors when the threat of renewed frost has passed and we have stable warm temperatures. Typically, that means June 10-15 for northern Germany, the first decade in May for central Germany, and the first decade in April for southern regions.

Tip: Search on Google for climate data for your city. Look at temperatures, based on data from recent years.

Sowing seeds: plan by the week.

make your own sowing calendar

Make a list of vegetable plants and annual flowers you want to plant this year. Immediately note which varieties you will grow and under what conditions, and include the expected planting dates. That way, you’ll know exactly when to plant your seedlings.

It’s handy to create a spreadsheet at the planning stage that includes the following information:

  • The name of the plant species and variety;
  • Planting location – outdoor or greenhouse (you can immediately plan the specific planting location and number of plants);
  • days for germination of the seedlings;
  • the age at which the seedlings were planted;
  • the best time to sow the seeds;
  • the dates for sowing the seedlings in the open field can now be easily calculated with the data you have in front of you.

Here is an example:

Germination period Age at the time for planting the seedlings. Best time to sow the seeds When to plant in the ground Number of true leaves at the time of planting
Eggplant 5-10 50-70 19.02-10.03 20.05 6-7
Sugar melon 3-7 25-35 20.03-1.04 20.05 3-4
White cabbage and cauliflower (early) 3-4 45-55 23.02-2.03 5.05 6-7
White cabbage, broccoli, Brussels sprouts, kohlrabi 3-4 35-50 14.03-29.03 25.05 4-6
Leek and onion 5-7 50-70 1.02-20.02 10.05 2-4
Cucumber 4-6 30-35 20.04-25.04 01.06 2-4
Peppers 7-12 50-60 10.03-15.03 25.05 6-8
Celeriac 10-16 60-70 23.02-03.03 15.05 4-5
Tomato 5-8 60-70 19.02-28.02 25.05 8-9

*This table is intended for mid-latitudes with moderate climate. If you live in the southern regions, you can start sowing and planting seedlings 5-7 days earlier, but in the northern regions – a week later.

It is also useful to have a separate column of expected fruiting (or flowering time for ornamentals). This can be calculated knowing the growing season of the particular variety. Sometimes the time of sowing seeds for seedlings is calculated based only on the time of fruiting.

Flowering and harvesting time is especially important for annual plants. After all, you grow them for this reason. To achieve a longer life, you can not only use varieties with different rates of flowering, but also vary the timing of sowing seedlings. By varying the age of the plants, fruiting will occur at different times. This will also help to correct the vagaries of the weather.

Also, do not overdo it. Remember that it is important to plant the seedlings in the open ground in time. Consider your options. How often are you willing to take the time to transplant seedlings? It is more convenient to do this in large quantities for different species and varieties. So it’s worth planning a few planting dates that fit the weather conditions and are convenient for you. Based on them, you can already calculate the dates for sowing seedlings, so that they mature in time for the planned planting dates.

Sowing seeds: Calculating sowing dates

sowing seeds in plastic containers

Now you can use the data entered in the table to calculate the sowing dates for seedlings. To do this, subtract the age of the seedlings and the number of days of germination from the planned planting date. If you need to separate seedlings, you should subtract an additional 4-5 days for seedling adjustment. This will give you a fairly accurate date for sowing your seeds. Considering the ambiguity of weather factors and different growing conditions, a variation of about 10 days is quite normal.

It would be optimal if you make your own calendar for sowing and planting seedlings. But in an average form for the cool temperate climate zone, the times will look like this:

Sow seeds: II decade of February – celery, chili, wild garlic, basil, oregano, parsley, mint, tarragon.
Sowing flower seeds: sweet peas (Lathyrus odoratus), levkojen (Matthiola), lobelia, bellflower (Campanula)

Sowing vegetable seeds: I. decade of March – early varieties of tomatoes for cultivation in a greenhouse, white cabbage, leeks, arugula, rhubarb.
II decade of March – late varieties (for cultivation in the open field) of tomatoes, peppers.
III decade of March – early varieties of tomatoes for cultivation in the open field, eggplants.

Sowing flower seeds: petunia, impatiens, marigold, larkspur, ornamental garlic, phlox.
Sowing herb seeds: watercress, dill

Sowing vegetable plants:
I. April decade – cucumbers for greenhouse cultivation, cauliflower, broccoli
III decade of April – zucchini, pumpkin, cucumber for cultivation in the open field, lettuce.

Sowing flowers: nasturtium, zinnias, forget-me-nots, cosmea, marigold (calendula), decorative sunflowers (helianthus, gerbera)
Sowing herb seeds: thyme, sage

Plant seedlings outdoors or in a greenhouse:
I. May decade – cucumber, tomatoes in the greenhouse;
II May decade – leeks, white cabbage, peppers and eggplants in a greenhouse;
III May decade – cauliflower, cucumber, squash, zucchini, celery, cabbage.

Plant seedlings in the open ground:
I. June decade – tomatoes, peppers.

If you take the time to plan and calculate the optimal dates for sowing seeds and planting seedlings in the ground, you can get healthy plants that require less care and provide a stable harvest, extend the fruiting season and make gardening easier and more productive.

Grow cuttings from seed: Here are a few basic rules that you should know

growing cuttings from seed tips

Before you start sowing, calculate how many seedlings you need. You can always buy the missing specimens, borrow from a neighbor or plant another plant in the vacant place. But if there are too many seedlings, it is always difficult to find a place for them on the plot or in the raised bed. This is mainly due to the psychological inability to throw away a live plant. Don’t make extra work for yourself – less is better. Here are some tips on what else to look for when sowing seeds.

How many seedlings are needed?

growing seedlings on the balcony

If you know the size of the greenhouse, bed or flower bed and the minimum distance between plants, you can easily calculate the required number of seedlings. Increase this amount by about 30% to allow for unforeseen circumstances.

The second criterion for the number of seedlings is the area of the window sills and other suitable areas available to you for germination. After all, growing at home requires quite a lot of space.

The right light for seedlings

special growing lamp for seedlings

Growing seedlings at home requires sufficient light. Without it, seedlings do not develop properly and grow poorly. Weakened seedlings are susceptible to various diseases. Therefore, you can not expect a rich harvest or abundant flowering.

Normal incandescent bulbs are less suitable for supplementary lighting of seedlings, but daylight fluorescent lamps (from 5500 K) and growth lamps are. However, since the pinkish-purple glow of the latter is unusual and even harmful to the human eye, they should be used in a set with special specular reflectors and/or simultaneously with the fluorescent lamps.

The light source should be as close as possible to the plants, especially in the first days after sowing seeds. Therefore, when installing the lights, consider the possibility of slightly changing the mounting height.

What should seedlings grow in?

growing pots from cardboard or egg carton

In preparation for the sowing season, also take care of the containers for growing seedlings. These should meet a few important requirements. First, they must have holes in the bottom and a separate tray for draining excess water. Second, choose containers made of a sturdy but lightweight material (wood or plastic) so they can be transported from one place to another when needed. They also need to be cleaned and disinfected after use; plastic is better in this case.

The material of the container must have a low thermal conductivity, so that the roots of the plants do not suffer from temperature differences. Cardboard or egg carton growing pots are often used, but some gardeners report mold growth.

Note: Do not place boxes of seedlings directly on a windowsill. Choose a wooden or Styrofoam base. There are also growing trays on feet on the market.

Potting soil for seedlings

disinfect potting soil for seedlings with boiling water

Growing seedlings at home requires a sufficiently permeable, loose and moisture-absorbing soil, so that water seeps better when watering and quickly reaches the roots of the seedlings. Most varieties need neutral pH soil, but some plants (such as gentians, ferns, and conifers) prefer acidic soil – just as they do outdoors.

You can buy ready-made potting soil at specialty stores, or you can make the sowing soil yourself . The mixture usually consists of turf and leaf soil (leaf humus) and coarse sand. Some gardeners add hydrogel to increase moisture.

Purchased soil does not need to be pre-treated. The self-prepared soil mixture should be doused with boiling water or heated with steam to prevent fungal diseases in seedlings.

Sowing seeds: the right depth

grow seeds in a seed tray

When all the preparations are completed, you can start sowing seeds. Here you should strictly follow the cultivation technology – it is different for each culture. The seeds of some plants (heliotrope, lobelia, petunia, etc.) germinate only in the light, they are simply spread on the surface of moistened substrate. Most seeds are placed at a depth of 1 to 4 cm and covered with soil.

For all crops, two rules apply: Seeds should be sown in previously moistened soil, and after sowing they should be covered with glass or transparent film to retain moisture. Once the seedlings appear, the film is gradually removed.

Optimal temperature for seedlings

Optimal temperature for seedlings

For each culture there are optimal, minimum and maximum temperatures for germination and subsequent growth. For example, begonias and petunias germinate at + 22-24 °C, while the optimal temperature for cabbage is + 8-10°C. All the necessary information can be found on the Internet or in the specialized literature. In any case, after germination, you should reduce the temperature by 2-3°C, so that the plants can better take root and only then continue to grow.

Note that lower temperatures are desirable even at night. This is because photosynthesis and respiration of plants depend on temperature. Since photosynthesis stops at night, but plants continue to respire, there is less need for high temperatures. Even with low light, the less light, the lower the room temperature should be.

How should I water my seedlings?

watering seedlings with spray bottle

Watering is also directly related to the amount of light. On a hot, sunny day, sprouts, especially those with large leaves, should be watered in the morning and evening. If there are few daylight hours and the weather is cloudy with low air temperature, 2 to 3 waterings per week are sufficient. Make sure that the soil in the container remains moist but does not become waterlogged.

Watering should be done with tap water. At the beginning of growth seedlings and small seedlings should be watered with a spray bottle, so as not to damage the weak stems and leaves.

Pricking out cuttings

Separate seedlings to improve growth

Growing plants should be transplanted into individual cups so they do not compete for nutrients and light. With good care and adequate light, most plants are ready for singling as soon as two to three leaves are present.

Seedlings are easily transplanted with a table fork or special pricking fork by removing a few plants from the seed tray and gently pulling the roots apart. While doing this, you can also shorten the central root with scissors to help the lateral roots form. The branched root system allows the plant to absorb nutrients more intensively and over a larger area. In this way, the root system remains superficial. The plant needs frequent watering because the roots do not penetrate deep into the soil to supply themselves with moisture. Shortening is not recommended for plants with taproot system.

pricking out cuttings singling

And this is how pricking goes: On the bottom of the individual cup soil is poured and abundantly moistened. Now poke holes in the substrate with the pricking fork. These should be large enough and deep enough to fit the roots of the seedlings without bending them. Now the seedling is placed straight into the hole and covered with soil.

Sometimes the small seedlings are also transplanted “bouquet”, a few plants in a cup. In this way, the roots are less damaged, and the plants more quickly acquire a decorative appearance.

Transplanting is done on a cloudy day, and then the seedlings are shaded for a few days. This allows plants weakened by transplanting to acclimatize and begin to grow again.

Hardening off seedlings

hardening off seedlings before transplanting them outdoors

The growing technique calls for hardening off seedlings a few days before transplanting them outdoors – this acclimates them to outdoor conditions.

Hardening off seedlings is carried out in warm, cloudy, windless weather, placing them outdoors for the first time for 10-15 minutes. Gradually, the time spent outdoors is increased. At the end of the week, when the weather remains consistently warm, the seedlings can be left outside overnight so that they become accustomed to the daily temperature changes. To avoid sunburn, seed pots should be shaded and protected with cover material at night. Hardening off seedlings prepares them for transplanting.

Transplanting seedlings outdoors

Planting tomato seedling in raised bed

As a rule, heat-loving plants are grown by seedlings, so transplanting to the open ground is possible only when the danger of another frost has passed. The prepared hole is filled with the necessary fertilizers and abundantly watered. When the soil has already dried a little, the seedlings are carefully removed from the cup and lowered into the prepared hole together with clods of soil, covered with soil and compacted.

Overlong tomato seedlings can be planted at an angle and, after cutting off the lower leaves, cover with soil to a greater height than in the tray. Side roots will then form on the stem below the surface, and the plant itself will take an upright position after a few days. Other types of plants should preferably be placed at the same depth as in the cup. After transplanting, mulch the soil, shade the seedlings and leave them without watering for a few days to allow the roots to spread and grow in search of moisture.

A few more tips

cats like to eat fresh greenery

Of course, if you are not satisfied with the seedlings you have grown, you can buy ready-made ones. When buying them, pay attention to their appearance: The seedlings should be strong, have a deep green color, and show no external injuries or signs of disease.

Do not forget to mark the seedlings when sowing and transplanting, indicating the type of plant, variety and date of sowing. It is also worth recording this information in your sowing calendar.

If you grow seedlings at home, keep them away from cats and other pets. They all like fresh greens and will not miss the opportunity to explore the taste of the seedlings. So make sure you plant the seedlings in a place inaccessible to animals.

Some species can be transplanted during the flowering period, for example, wild pansy (Viola tricolor var. hortensis), petunias, marigolds and some others.

healthy seedlings in plastic cups