Container gardening in a greenhouse works best with the right pot size, a light potting mix (never garden soil) and steady watering. Pots let you move plants to the best light, swap crops quickly and keep pests from spreading through the soil. With a few simple habits, almost any vegetable, herb or flower can thrive in a pot under glass.
ā Quick answer
- Pick pots with drainage holes. Don't put gravel in the bottom; it makes drainage worse.
- Use a soilless potting mix. Garden soil is too heavy for containers.
- Match pot size to the crop: a tomato needs at least a 5-gallon pot, lettuce only about 2 quarts.
- Check pots daily in warm weather. Water when the mix feels dry a couple of inches down.
- Feed regularly. Starter fertilizer in bagged mixes lasts only a couple of weeks.
We are a small, woman-owned greenhouse business in Georgia. Many of our customers grow almost everything in pots, especially in their first year. These are the tips we share with them most often, backed by university extension advice.
Why try container gardening in a greenhouse?
A greenhouse floor is valuable space. Containers help you use every inch of it, from the floor to the top shelf.
- You control the soil. Each pot gets fresh, clean mix, with no heavy clay or old soil diseases.
- Plants can move. Shift sun-lovers to the bright side and tender plants away from cold glass.
- Pests stay put. A sick plant can be isolated before the problem spreads.
- Easy crop changes. Swap winter greens for summer tomatoes without digging beds.
- Great on hard floors. Pots work on pavers, gravel or concrete, where beds can't.
- Better use of height. Shelves and hanging baskets add growing space above the floor.
There are trade-offs too. Pots dry out faster than the ground and need regular feeding. The tips below cover both.
What are the best containers for a greenhouse?
Any pot with drainage holes can work. The material changes how fast the mix dries and how heavy the pot is. NC State Extension groups containers into three types:
| Material | Holds water? | Weight | Good to know | Best for |
|---|---|---|---|---|
| Plastic | Well (non-porous) | Light | Cheap and easy to move; can fade in strong sun | Most vegetables and starts |
| Terracotta / clay | Dries fast (porous) | Heavy | Breathes well; can crack if wet pots freeze | Herbs, succulents, cacti |
| Glazed ceramic | Well | Heavy | Attractive; check for a drainage hole | Patio plants, citrus |
| Wood (cedar, redwood) | Medium | Medium | Cedar and redwood can last about 10 years unpainted | Large boxes, herbs |
| Fabric grow bags | Dries fast | Very light | Roots get plenty of air | Potatoes, tomatoes |
Fabric grow bags are not in the NC State groups; they behave like a very porous pot. Dark pots also soak up heat in summer, which can cook roots in a hot greenhouse.
š A myth worth dropping: many guides still say to put gravel or rocks in the bottom of a pot. NC State Extension says never to do this. Water collects in the mix just above the gravel, so the roots sit wetter, not drier.
What size pot do greenhouse vegetables need?
A pot that is too small dries out fast and stunts the plant. Here are minimum sizes from NC State Extension's container guide. Bigger is almost always better.
| Crop | Minimum pot | Plants per pot | Notes |
|---|---|---|---|
| Tomatoes | 5 gallons | 1 | 12 to 24 in deep |
| Eggplant | 5 gallons | 1 | 12 to 16 in deep |
| Peppers | 2 gallons | 1 | 12 to 16 in deep |
| Beans, peas | 2 gallons | A few | Peas about 12 in deep |
| Cucumbers | 1 gallon | 1 | Give them a trellis |
| Kale, collards | 3 gallons | 1 | Pick outer leaves often |
| Lettuce, chard, radishes | 2 quarts | Several | Great for shelves |
| Potatoes | 30 gallons | A few | Grow bags work well |
š” Our tip: a 2-gallon pepper pot fits neatly on most greenhouse shelves. Save the floor for big tomato and cucumber pots, which need room to climb.
What potting mix should I use in greenhouse containers?
Use a soilless potting mix. NC State Extension notes that field soil is no longer used in containers. It holds too much water, packs down and can carry weeds, insects and disease.
- Look for: peat moss or pine bark with perlite or vermiculite. These keep the mix light and airy.
- Compost: fine in moderation. Keep it to about 15 to 40 percent of the mix.
- Sand: only coarse builder's sand, never fine play sand.
- Fresh each year: repot healthy plants in new mix, ideally in early spring.
Homemade compost is a great add-in. Our Aerobin 400 composter is insulated, so it keeps working in cooler weather, and you never have to turn the pile.
How much potting mix will I need?
Pots are sold in gallons, but potting mix is sold in cubic feet or quarts. This quick formula converts between them.
š Potting mix formula
Cubic feet of mix = Total pot gallons Ć 0.134
Bags needed = Cubic feet Ć· Cubic feet per bag
1 gallon = 0.134 cubic feet Ā· Check the bag label for its size Ā· Buy about 10% extra for settling
š§® Worked example: filling pots for a Riga 4
- The Riga 4 has 135 sq ft of floor space, plus room for shelves along the sides.
- On the floor: 8 tomato plants in 5-gallon pots = 40 gallons.
- On the shelves: 10 pepper plants in 2-gallon pots = 20 gallons.
- Total: 60 gallons Ć 0.134 = about 8 cubic feet. Add 10% = about 8.8 cubic feet.
- With 2-cubic-foot bags: 8.8 Ć· 2 = 4.4, so buy 5 bags.
Bag sizes vary, so always check the label before you buy.
How often should I water containers in a greenhouse?
There is no fixed schedule. A greenhouse warms up fast, so pots can dry out in a single sunny day. Check them, don't guess.
- Do the finger test. Push a finger a couple of inches into the mix. If it feels dry, water.
- Water deeply. Keep going until water runs from the drainage holes. NC State notes a dry 5-gallon pot can take 2Ā½ to 3 gallons to wet fully.
- Water in the morning. Leaves dry before evening, which helps prevent disease.
- Flush now and then. If a white crust forms on the mix, run water slowly through the pot for a few minutes to wash out salts.
- Expect more watering in summer. Large plants in hot weather may need water every day.
Busy schedule? The MONT Automatic Greenhouse Watering System hangs from the ceiling and runs on a commercial digital timer. For more on water needs, read our guide on how much water plants need in a greenhouse.
How do I feed plants growing in containers?
Every watering washes a little food out of the pot. That is why container plants need more regular feeding than plants in the ground.
- At planting: mix in a slow-release (controlled-release) fertilizer.
- During the season: top up with a liquid or granular feed as the label directs, since watering keeps washing nutrients out.
- Read the label: follow the product directions and don't overdo it. Too much fertilizer can burn roots.
How do I use shelves and space for container plants?
Height is free growing space. Benches, shelves and hanging baskets can nearly double what you grow in the same footprint.
- Top shelves: seedlings, herbs and lettuce in small pots. They get the most light.
- Lower shelves and floor: big pots and heavy plants like tomatoes and peppers.
- Slatted or vented shelves: let water drain and light pass to the plants below.
- Waist-high tables: easier on your back and keep pots off cold floors in winter.
Here are a few of the shelves and tables our customers use for pots:
| Product | Fits | Key detail | Approx. price* |
|---|---|---|---|
| Shelves for Riga Greenhouses | All Riga models | 10 in or 25 in deep | From about $319 |
| MONT Shelves and Workbenches | MONT 8 ft greenhouses | 24 in deep; 8x8 kit holds up to 600 lb | From about $400 |
| Eden Deep Root V-Shaped Garden Table | Any greenhouse or patio | Up to 16 in deep; sits almost 3 ft high | About $211 |
*Prices checked in October 2026. Prices can change and sales may apply, so click the model name to see today's price.
š About prices: manufacturers update their prices during the year, and we often run sales and promotions. The price on the product page is always the current one. Prices in this article are a guide from when we wrote it (October 2026), not a quote or guarantee. Found a lower price for the same model at an authorized retailer? We offer a Price Match Guarantee - please check the rules first. Call us and we will confirm today's price and any current deals.
For more ideas, see our guide to the best shelves for a greenhouse kit.
Which plants grow best in greenhouse containers?
Most compact crops do well in pots. Choose "patio" or "bush" varieties when you can; they are bred for containers.
- Vegetables: tomatoes, peppers, eggplant, cucumbers, bush beans, peas, kale and chard.
- Salad greens: lettuce, spinach and radishes in shallow pots or trays. Our guide to growing greens in winter shows how to keep them going through the cold months.
- Herbs: basil, parsley, chives and thyme.
- Flowers and succulents: geraniums, begonias, cacti and succulents, which like fast-drying clay pots.
- Fruit: figs need at least 10 gallons, and strawberries do well in pots about 8 inches deep.
What mistakes should I avoid?
- Pots without holes. Roots drown fast. If a pot has no hole, set a smaller pot with holes inside it.
- Garden soil in pots. It packs down and drains poorly.
- Pots that are too small. They dry out by afternoon and stunt growth.
- Leaving clay pots out in a freeze. Wet terracotta can crack when it freezes.
- Forgetting airflow. Crowded pots and still air invite mildew. Space plants and vent on warm days.
Frequently asked questions
Is it better to grow in pots or in the ground in a greenhouse?
Both work. Pots give you control over soil, easy crop changes and fewer soil pests. In-ground beds hold water longer and need less watering. Many growers use beds along the sides and pots on shelves.
What size pot does a greenhouse tomato need?
At least 5 gallons for one plant, according to NC State Extension. Bigger pots of 10 gallons or more hold more water and are easier to manage in summer.
Can I use garden soil in containers?
It's best not to. Garden soil is too heavy for pots, drains poorly and can carry weeds and disease. Use a light, soilless potting mix instead.
Should I put rocks in the bottom of my pots?
No. A gravel layer makes water collect in the mix above it, so roots stay wetter. Use pots with drainage holes and fill them with mix all the way down.
How often should I water greenhouse container plants?
Check daily in warm weather and water when the mix is dry a couple of inches down. Big plants in summer may need water every day.
Can I grow in containers in a greenhouse all winter?
Yes, with cold-hardy crops like lettuce, spinach and kale, or with heat for warm crops. Keep pots off cold floors on shelves or tables.
Setting up your container greenhouse?
We are a small, woman-owned business in Georgia, and we answer every question personally. Tell us what you want to grow, and we will help you choose the greenhouse, shelves and watering setup. We offer free shipping to the continental US and optional assembly crews.
