If you have a greenhouse (or are thinking of setting one up ) and want to get the most out of it, you need more than just a few pots and good intentions: you need a clear plan of what to plant, when to plant it, and how to care for each crop in a protected environment. The goal isn't just to bring spring forward, but to make your greenhouse the heart of your year-round supply of vegetables, fruits, and herbs.
Throughout this guide, you'll find a month-by-month plan, organized by season, crop type, and even lunar phase , along with key maintenance tasks and plenty of practical tips for managing temperature, humidity, pests, and soil. It's a long and detailed article, perfect as a reference manual whether you're starting from scratch or have years of experience battling seedlings and treacherous frosts.
Why a growing calendar is your greenhouse's best ally
A greenhouse isn't just an indoor garden: it's a controlled microclimate where you decide on light, temperature, humidity, and the timing of your crops . Without a clear schedule, it's easy to miss planting dates, overcrowd the plants, deplete the soil, or end up with empty beds that could be producing.
With a well-thought-out annual plan, you can link sowing and transplanting to ensure there's always something growing and something harvesting , avoiding the typical peaks of abundance (mountains of zucchini all at once) followed by months of scarcity. Furthermore, a calendar allows you to organize crop rotations and companion plantings that protect the soil, reduce disease, and improve water and nutrient use. For ideas on how to organize the layout and make the most of your space, consult studies on horticultural crop distribution.
It's not about following a rigid scheme, but about using this framework as a guide and adapting it to your local climate, the size of your greenhouse and the type of gardener you want to be : more self-sufficient, more experimental or more practical and simple.
Types of greenhouses and their influence on what you can plant
Before you start planting, it's important to be clear about what type of structure you have , because this will determine how much you can extend the season, what crops it will best support, and what investment in heating or shading you will need.
Classic glass greenhouse
Glass greenhouses are the classic choice: plenty of natural light, high thermal inertia, and impeccable aesthetics . They are ideal for crops that require a lot of light (tomatoes, peppers, delicate flowers) and allow for more stable temperatures if properly sealed. However, they require more maintenance (cleaning the glass, checking the seals) and a higher initial investment.
Plastic Greenhouses
Structures with plastic coverings (polyethylene, polycarbonate, etc.) are the most common option because they offer good value for money and adapt to almost any space . Plastic retains heat well, although it can degrade and lose transparency over time, so the sheeting needs to be replaced when necessary. For most home gardens, a plastic tunnel or shed is more than enough to grow vegetables year-round.
Tunnel greenhouses
Growing tunnels are arched structures, usually made of metal, covered with flexible plastic. They are perfect for medium to large areas and for intensive vegetable crop rotations . They are relatively easy to assemble, the cost per square meter is low, and they allow for the mechanization of some tasks. However, good ventilation is essential , as they heat up quickly in spring and summer.
How to set up the greenhouse for crops to thrive
A beautiful structure that isn't properly managed becomes an oven in summer and a freezer in winter. Therefore, beyond the covering, it's crucial to place the greenhouse in the right location and equip it with basic climate control systems.
location and orientation
For most climates in Spain, the most common orientation for a greenhouse is east to west to make the most of the winter sun , although in some areas a north-south orientation is preferred to distribute the radiation to both sides. In any case, try to avoid permanent shadows from trees, walls, or buildings , especially in autumn and winter, when sunlight is most precious.
It's also important to consider the wind: a highly exposed facade can stress the structure and significantly increase heat loss in winter . A nearby hedge or windbreak helps considerably.
Temperature control
The key is to moderate the extremes. In winter you need to retain heat, and in summer you need to release it. At a basic level, there are three pillars: ventilation, shading, and, if necessary, heating.
- Large windows and doors on opposite sides to create airflow on hot days.
- Automatic openers of skylights or windows that open automatically when the temperature rises.
- Light heating (stove, heating cable on the floor, small electric radiators) in cold areas or for very delicate seedbeds.
- Use of thermal mass with water drums that absorb heat during the day and release it at night. See ideas about use of bottles and jerrycans in the garden to improve thermal inertia.
Irrigation and humidity
In a greenhouse, water can be either friend or foe: too much moisture and you'll have mold everywhere, too little and the plants will be stressed. Ideally, you should install a well-zoned drip or micro-sprinkler irrigation system to control water in each area according to the crops grown.
Drip irrigation systems allow you to water early in the morning or at dusk , wetting the soil and not the foliage, which reduces disease. A simple hygrometer will tell you if you're overwatering; if you see a lot of condensation on the plastic sheeting, you need to improve ventilation and perhaps water less frequently but more deeply.
A year in the greenhouse: what to do in each season
To organize the information in a manageable way, we'll first look at the year by seasons within the greenhouse, and then go into detail month by month and by crop type. Keep in mind that in a protected space, the dates are slightly earlier than in an open-air garden.
Winter: The quiet work that makes a difference (December – February)
While the outdoor garden seems dormant, the greenhouse becomes your headquarters for planning, propagation, and maintenance . Here, much of the harvest for the rest of the year is decided.
These months are the perfect time to sow long-cycle crops in seed trays (onions, leeks, celery, some perennials, and flowers) that need plenty of time to develop roots before being transplanted outdoors. Use heat mats or heating cables to keep the potting mix between 18 and 24°C, the range in which most vegetable seeds germinate.
If you planted cold-hardy vegetables in the fall (spinach, kale, winter lettuce, chard, claytonia, some brassicas), you'll continue to harvest fresh leaves for much of the winter, provided you protect against severe frosts with double protection (greenhouse + indoor thermal blanket). To protect the leaves, it's advisable to use techniques like those explained in how to protect leafy green crops.
These months are also ideal for thoroughly cleaning the structure : plastics or glass, fans, gutters, irrigation systems and, above all, for checking and improving the soil with compost, well-ripened manure or cut green manures.
Spring: the great acceleration (March – May)
With the increase in daylight hours, the greenhouse transforms into a seedling factory, ready to be transplanted outdoors or kept indoors to continue producing . It's the busiest time of year for trays, pots, and transplanting.
During this phase, you sow and transplant warm-weather summer crops such as tomatoes, peppers, eggplant, cucumbers, zucchini, and melons. At the same time, you can directly sow short-cycle, cool-weather vegetables (radishes, early carrots, beets, spinach, lettuce) that will be harvested before the summer crops take up all the space.
Ventilation becomes a daily necessity, because a sunny April day can bring the greenhouse to critically high temperatures if you don't open the doors and windows. It's also crucial to start staking and training tomatoes and cucumbers to gain vertical space and improve air circulation.
Summer: production explodes, heat stress increases (June – August)
In summer, the greenhouse experiences its most spectacular… and most delicate moment. Its structure is filled with vigorous plants laden with flowers and fruit ( tomatoes , peppers, eggplants, cucumbers, pole beans), but the heat can become a serious enemy.
Prolonged temperatures above 30-32°C cause many crops to abort flowers and drastically reduce yield . To prevent this, use various methods: 30-50% shade netting, cross ventilation, fans, drip irrigation, and, if you're in a very hot area, some evaporative cooling.
Even so, it is time to take advantage of the warm soil to sow the plants that will form the basis of autumn and even winter : broccoli, cauliflower, various cabbages, chard, late spinach, as well as a new round of lettuces.
Successive planting is recommended : as soon as an early crop (e.g., spring spinach) completes its cycle, remove the plants, add some compost and plant another crop (beans, a cover crop or an early brassica).
Autumn: second spring and preparation for winter (September – November)
With temperatures easing, the greenhouse is breathing again. It's a fantastic time to stock up on leafy greens, brassicas, and root vegetables that will keep the harvest going well into winter.
As the days get shorter, you take down shade netting, close vents earlier to retain heat, and start adding light insulation (bubble wrap on the north side, weatherstripping on doors and windows, etc.). It's also the time for a thorough cleaning of summer crop debris to eliminate breeding grounds for pests and fungi.
Many perennial herbs (rosemary, thyme, sage, oregano) and strawberries can be planted at this time to develop a strong root system before the onset of cold weather . Soil enriched with compost at this time will result in much healthier and more productive winter crops.
Monthly calendar of what to plant in a greenhouse
In addition to a seasonal approach, a quick outline of which crops are best suited to each month can be helpful if you have a greenhouse . The dates are approximate and based on a temperate climate; always adjust for your specific area.
- January: Swiss chard, onion, endive, carrot. It's best to protect them well from frost and use sheltered seedbeds.
- February: Spinach, lettuce, radish, cabbage. Ideal in seedbeds with moderate and controlled watering.
- March: Tomato, pepper, eggplant, zucchini. Sow in a heated seedbed or directly in a well-protected greenhouse, with an initial application of fertilizer.
- April: Cucumber, JewishSweet corn, melon. Transplant indoors or outdoors depending on the climate, watching for emerging pests.
- May: Watermelon, pumpkin, basil, early potatoes. Frequent watering, stakes ready, and extra fertilization.
- June: Celery, cauliflower, leek, and carrot for autumn. Be careful with the heat, mulch, and water deeply.
- July: Lettuce, spinach, chard, and radish for autumn harvest. Best with some partial shade and generous watering.
- August: Endive, broccoli, various cabbages, spinach. It can be sown directly, protecting it from strong sunlight.
- September: Broad beans, peasSwiss chard, winter lettuce. A good time to sow is late afternoon to prevent fungal growth.
- October: Garlic, onion, spinach, winter carrots. Mulch for the cold and less frequent watering.
- November: Broad beans, peas, turnips, leeks. It provides good protection from the wind and offers some moderate fertilization.
- December: Garlic, endive, radish, early onion. In cold areas, it's best grown in a greenhouse with extra protection against frost.
Advanced planning: the garden month by month in detail
If, in addition to managing a greenhouse, you also have an outdoor vegetable garden, you'll want to get a general overview of what to plant and harvest each month, both indoors and outdoors . Below is a concise summary of the types of activities by month (oriented towards a temperate climate like that of much of Spain).
January and February: start of the cycle
In January the landscape may seem still, but in reality, this is when everything that follows is set in motion: orders and exchanges of seeds are made, potatoes are germinated, fruit trees are pruned, and protected seedbeds are prepared for garlic, onions, lettuce, asparagus, turnips, carrots, etc. In areas without severe frosts, some vegetables can even be sown directly.
February continues in the same vein, with increased activity in seedbeds for onions, cabbages, lettuce, leeks, tomatoes, and other nightshades . Radishes, carrots, spinach, and beets are also sown directly, and already established onions and lettuces are planted out with some protection in case of a late frost. In the greenhouse, it's a good time to add mineral amendments (rock flour) if the soil requires it.
March and April: sowing at full speed
With the arrival of March, the days lengthen and the grass begins to grow vigorously, as do the weeds in the vegetable garden. In sheltered areas and greenhouses, slugs and snails thrive , so it's advisable to use barriers of sand, basalt, or traps.
The seedlings of zucchini, cabbage, cauliflower, and fennel are started , and potatoes are planted for the early season. In April, the full summer arsenal is added: eggplant, peanuts, melon, peppers, cucumbers, watermelons… almost everything can be sown or planted, provided the risk of frost has passed or you have a greenhouse to protect it.
At this stage it is essential to have the irrigation system ready and the plots well aerated and weeded , because competition from weeds can be brutal just as the crops are starting up.
May and June: flowering, watering and the first big harvests
May is the month of flowers and weeds in full force. Weeding becomes routine, and watering becomes essential, both inside and outside the greenhouse. Summer vegetables continue to be sown and planted , and the harvest of early potatoes, lettuce, cauliflower, spring onions, and other vegetables begins.
In June, the landscape turns golden: the grain ripens and everything is prepared for the harvest. In the vegetable garden and greenhouse, all sorts of vegetables are picked (zucchini, cucumber, lettuce, potatoes, carrots, beets) , and corn and beans are sown for drying, among other crops. The meadows are also cut for hay, and alfalfa is dried, which will be essential for feeding the livestock throughout the rest of the year.
July and August: peak harvest and autumn forecast
July is marked by the grain harvest, straw baling, and grazing of stubble fields. In the greenhouse, the summer plants are thriving, but it's important not to get complacent: it's time to start sowing vegetables for autumn and winter (cabbage, broccoli, endive, spinach, etc.).
In August, although the heat is intense, the pace of autumn crop planting continues , the grain harvest and sorting are completed, a second hay cutting is made, and a large quantity of fruit is harvested (peaches, early apples, figs, early grapes, etc.). It's a good month to calmly review forecasts, seeds, and structures , taking advantage of the warmest hours for lighter tasks.
September, October and November: transition and preparation for the next cycle
In September, with the return to routine, sales of fresh produce usually pick up. It's time to sow spring garlic, cabbages, winter lettuces , and prepare the land for autumn cereals with fast-growing green manures.
October is a month of decisions: major crop rotations are defined, plots are prepared for winter and spring crops, and broad beans, peas, radishes, and leek and onion seedlings are sown. Roofs, chimneys, and storage sheds are also inspected, because winter is just around the corner.
In November, cereals (oats, barley, rye, wheat) are sown, and green manures are added to the plots that will be cultivated later. The vegetable garden is filled with carrots for spring, garlic for fresh consumption, cabbages, and spinach . Field margins and hedges are cleared, compost heaps are turned, and animal bedding is adjusted, carefully calculating forage and grain reserves.
December: relative pause and organization
December revolves around the house and its outbuildings: machinery and tools are repaired, firewood is chopped, fruit trees are pruned when the weather permits, and the threshing of legumes is completed. It's the time to take stock of the season, plan for the next, and ensure there are enough seeds and plants for the coming year . Compost can now be brought to the fields to facilitate spring fertilization.
Choosing the right spacing between plants and combining crops wisely
The success of a greenhouse depends not only on what you plant, but also on how you arrange each crop and what you plant alongside it . Proper plant density and companion planting reduce pests, improve nutrient uptake, and prevent plants from competing with each other.
Some practical examples based on the experience of well-planned gardens:
- Tomato: Space rows about 60 cm apart and plants about 50 cm apart. It grows well with garlic, asparagus, basil, carrot, celery, corn, onion, parsley, pepper, leek and radish. It's best to avoid it near potatoes.peas, fennel or cucumbers.
- Cauliflower and broccoli: Rows 40 cm apart and plants 40-50 cm apart. They do well with beans, peas, lettuce, celery, tomatoes and potatoes, but do not do well with garlic, onions and strawberries.
- Curly lettuce: Rows 30 cm apart and plants 15-20 cm apart. Excellent companion for onions, beets, carrots, cabbages, cucumbers, beans, strawberries, turnips, leeks and peas; less so with endive and parsley.
- Carrot: rows about 20 cm apart and plants every 3-6 cm. It associates well with onions, leeks, radishes and peas; it is best not to mix it with beets, new potatoes, celery, fennel or parsley.
The general idea is to alternate botanical families and functions (leaf, root, fruit, flower) so that they do not always extract the same nutrients, take advantage of different root depths and break cycles of specific pests.
Tools and soil management, irrigation and indoor climate
A productive greenhouse needs a minimum of horticultural infrastructure: you don't have to go crazy, but you do need a small arsenal of efficient tools and well-maintained soil.
For tools, it's advisable to have a rototiller or hand hoe depending on the size, a shovel, rake, planters, wheelbarrow, tarps or baskets, weed barrier fabric if you use it, gloves, and a good, suitable irrigation system (hoses, spray guns, drip irrigation, etc.). All of this makes it easier to work with greater precision and less physical effort.
The soil is the foundation of the garden, and its health is maintained with mature compost, organic fertilizers, crop rotation, and green manures . Plant waste from the garden itself, mixed with well-rotted manure, is a treasure: it provides humus, improves soil structure, and enhances water retention.
Regarding indoor humidity and temperature management, the strategy is clear: ventilate to avoid excessive heat and condensation, water judiciously, and provide shade when necessary . Moderate but thorough watering, preferably at the end of the day, helps the water be better absorbed and prevents the development of diseases linked to excess humidity.
Lunar calendar and its practical use in the greenhouse
The topic of the moon in the garden generates endless debate. There is no absolute scientific consensus, but many gardeners notice differences when respecting lunar phases , especially in the quality of their harvests and the behavior of certain crops.
A practical way to apply this is to distinguish according to the part of the plant you are going to consume:
- Fruit: tomatoes, peppers, zucchini, cucumbers, melons, watermelons…
- Sheet: lettuce, cabbage, turnip greens, spinach, chard…
- Root: carrots, onions, garlic, turnips, beets…
- Flower: broccoli, cauliflower, artichoke…
Applying the most widely accepted theory:
- Full moon: The sap would tend to concentrate in the aerial part, so it is considered a favorable time for sow leafy vegetables (lettuce, spinach, etc.).
- last quarter: The force would be directed more towards the roots, a moment that is used to root vegetables (carrot, beetroot, onion…).
- First Quarter: The sap would rise again, and many gardeners take advantage of this to sow fruit crops (tomato, pepper, beans…).
- New Moon: usually reserved for tasks of maintenance, weeding and light pruningavoiding significant planting and harvesting.
If you're just starting out, don't get too hung up on it: focus on learning the basics of greenhouse management and, once you've got it under control, try coordinating some plantings with the lunar calendar for a year or two and draw your own conclusions.
Seeds or seedlings? How to combine both options
A very common question is whether it's better to sow everything from seed or buy already grown seedlings. Each option has its pros and cons, and in a greenhouse, the most sensible approach is usually to combine both.
Sowing seeds allows you to save money and choose specific varieties (heirloom, local, resistant), as well as enjoy watching the plant's entire life cycle. The problem is that some seeds are delicate to germinate and require very precise temperature and humidity conditions; if something goes wrong, you'll either have no plants or you'll be too late in the season.
Seedlings (transplants) make your life much easier because they have already passed the critical germination and first leaf stage . They shorten the cycle to harvest and save space in seedbeds, at the cost of a higher cost per unit and less variety available.
If you're just starting out, it's very practical to begin by transplanting key crops (tomatoes, peppers, spring lettuce) and reserving part of the greenhouse for experimenting with your own or purchased seeds . Over time, you'll gain experience and be able to rely much more on your own sowing.
Turning your greenhouse into a year-round productive space involves combining calendar planning, rotations, and companion planting with good control of the indoor climate, water, soil, and pests, mixing sowings from seed with purchased seedlings or those from your own nursery; with this balanced combination, your structure will go from being a simple shelter for four plants to a true engine of fresh vegetables, fruits, and herbs month after month.
