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While we might not be done with winter just yet, we are on the way out! This has been a relatively mild season on average, I don’t aim to discount the strange week long storms that popped up every now and again over the past few months. However, despite how much you enjoyed or didn’t enjoy the weather, we are all looking forward to the spring. Spring is the season of growth and rebirth, a beautiful time full of fragrant flowers and the return of outdoor activities. Sorry to get you excited prematurely, you still have to wait a bit for the warm weather and fields full of flowers, but March is a very important month if you want to ensure you have a bountiful spring in your greenhouse. This is the time of year where you can truly start growing without relying entirely on artificial light and heat. The sun begins to stick around a bit longer in the afternoon and the daily highs are generally a bit warmer. While many of the tips for growing in your greenhouse this month may be similar to those I’ve told you before, they are still useful. It’s almost like gardening in a controlled micro climate can be done in the same way all year round… Regardless, March is an important month for a whole lot of plants in your greenhouse and your real gardening work starts now!
March is generally a very windy month, according to historical adages, but this March is also expected to be rather wet. At least that’s the forecast in my neck of the woods, in the beautiful Pacific Northwest. With the upcoming wind and rain, you may want to check on your greenhouse and make sure everything is up to stuff. Check for any cracks or drafty areas in case the winter weather was less than friendly to older greenhouses. Aside from integrity checks, you will likely have a lot of cleaning to be done. If you were smart and/or active over the winter and kept your greenhouse in clean, working order, you can go ahead and skip the rest of this paragraph. Or keep reading, it’s your life. Cleaning can be a real pain, but vital. A cluttered and dirty greenhouse will be much less conducive to cultivating a healthy growing environment. Dirty spaces can aid in mold and fungal infection growth which can be harmful for your plants. Clutter is not only ugly but it can also take up precious growing space. The number one complaint, in fact the only complaint, I’ve heard from customers is that they didn’t buy a bigger greenhouse. So if you want to grow as many plants as possible, it’s a good idea to clean up and clean out your greenhouse before you start trying to grow anything.
Once you’ve finished your chores and are ready to plant, make sure you have either passed the last frost of the season, or are prepared to deal with it. Nighttime temperatures should be at a minimum of 45°F to make sure your plants don’t suffer from frost. If you are just starting plants, it’s less important to heat the entire greenhouse. Instead, focus your heating on the soil in which you are growing. There are a few ways to deal with this. A cheap way to deal with this using household items could be something like wrapping flower pots in old towels or blankets in an effort to insulate the soil. This can be effective if the nighttime temperatures are not getting below 45°F, but are generally sitting near that point. If the temperatures are going to get significantly colder, you may want to explore more energy intensive options. Soil heating cables are elegant solutions to your soil heating needs. These cables can be run through your planter of choice and will radiate heat into the soil around it. This way your soil maintains warm enough temperatures to promote seed germination without having to spend and arm and a leg on heating an entire greenhouse. Simply pour dirt into your planter of choice, lay the cable in a way that spreads it evenly atop the first layer of soil, then cover the cable in soil deep enough to allow the planting of seeds.
Not only is March a great month to start up new plants, it’s a time when you can keep up with plants you started on months ago. Orchids and other root bound perennials are ripe for repotting this month. Check on them and see how their growth is going, if they are getting too big for their current pot, it’s time to get a new one. Repot these plants to ensure they continue to grow and aren’t harmed or wanting for extra space. Flowering chrysanthemums should be about ready to repot in 5” to 6” pots by the end of the month. Once established, harden them off in a cold frame prior to planting outside for summer blooms. Tuberous begonias can be brought inside and placed in trays filled with peat. Once leaves begin to appear, go ahead and repot! This ensures you will have healthy and beautiful begonias for another year. Dahlia tubers similarly should be dealt with at this time. The difference being they want a mixture of sand and peat. Dahlias will then begin to root, which is great if you want some more plants! Simply cut the roots at points where each snippet contains one tuber with minimum one shoot coming out the top. These should then be planted in rich compost and voila, you’ve got yourself free plants!
If you’ve been maintaining your greenhouse garden year round, now is a great time to sow things like gloxinia and cineraria. Harvest your salad greens, mushrooms, radishes, chicory and any other produce you’ve been growing over the winter. Once harvested, many of these can be re-seeded for another harvest down the line. For seeds that were started last month, transplant them once their first pair of true leaves begin to form. This is when the rhizome really begins to form and the plants need more room.
As far as fruiting plants such as strawberries and melons, take some extra precautions. These types of flowering fruits require pollination and because of this, care must be taken during the early flowering stages. While flowers are forming, refrain from damping down your greenhouse. Too much excess moisture can block the pollination process and prevent fruit formation. Once the fruit has actually set, you can begin damping down your greenhouse once more. To “dampen down” your greenhouse, simply water the floor of your greenhouse with a garden hose or watering can. This can help cool off the greenhouse as well as aid in the formation of humidity. Both of these can help you in the growing process but should be monitored as you don’t want to overwater or create too much humidity.
Above all this month, pay attention to ventilation and watering! With the somewhat random temperature changes we can experience it is important to stay on top of venting your greenhouse and giving your plants the water they need. Wide fluctuations in temperatures can wreak havoc on your plants, so make sure the environment inside your greenhouse is as stable as possible. Try to keep the ambient temperature in the range of 45° F-65° F if you are keeping a cool growth greenhouse. Adjust accordingly if your chosen plants require warmer temperatures. Now that the sun is visiting us more frequently, once a week is better than never, make sure you are properly venting your greenhouse. Open the roof and side vents in the morning when you are expecting a lot of sun and open the front door around midday. Once the sun starts to drop, go ahead and close up the greenhouse to make sure you trap in as much heat as you can. With this being a time of starting new plants, you might want to invest in some shade fabric. Too much intense direct sun light can burn seedlings so making sure they are getting partial shade during the day is essential. Your greenhouse is likely set up in a place that optimizes sunlight so partially shading the glazing or creating a shady spot in which to hide some of your more sensitive plants will really help you out in the long run. Dampen down your greenhouse floor as needed. As mentioned earlier, some plants are more sensitive to excess water. Inversely, if you are using your greenhouse to continue the growth of mature plants, increasing access to water and fertilizer will help plants that are showing signs of active growth. While you do want to limit the amount of water you are giving younger plants, be sure that they are not drying out. More mature plants may be able to withstand a light drought but seedlings can be more sensitive.
While the beginning of March can be quite windy and still a little cold, the latter half of the month brings with it a generally calmer climate. The warmer, less intense weather towards the end of the month while pleasant, marks the start of pest season. Whitefly, aphids and red spider mites in particular are a big problem in the Pacific Northwest. Taking preventative measures at the start of the month can go a long way in pest control. Make sure you are limiting the amount of excess humidity and standing water in your greenhouse. Nothing is more welcoming to pests than a warm environment, safe from the outside weather, filled with tons of food and water. Stock up on things like Sluggo Plus and Neem Oil so you’re prepared in case of an outbreak. Loupe Magnifiers are also a great tool for identifying what exactly your pest problem is. It could be whitefly, it could be some cottonwood seeds that got in through the vent, sometimes you never know what it is. But one of these magnifiers will help you solve the case.
March is a busy month, there’s no doubt about that. There is a lot to do both inside your greenhouse and out. It’s a lot to keep up with! But you’re doing great, I'm sure of it! Just remember to breathe and take a look around at all the wonderful things you’ve done so far this year. Thanks again for reading, until next week!