Hi, I live in Spain and I have a question about topdressing. It’s very hot here and the sun is very strong, which causes the topdressing to dry out very quickly. If I were to water every time it dries out, I’d spend the whole day watering, and I’m worried that doing so would lead to too much water accumulating below. What do you recommend—should I water every time the surface dries out, or should I wait?
Good question. I just came back from Madrid where I visited the collections of Luis Vallejo, David Benavente and the Royal Botanical Garden. I didn’t see a lot of green moss there. But still there were some trees planted on stone slates and their root ball was covered with moss. So it must be possible.
I have a similar problem where I live, in Berlin Germany. The sun isn’t as intense but the microclimate on my south facing balcony is very dry and hot as well. In my experience, moss only starts to grow under trees with a dense canopy that provides shade and keeps the moisture under it. Some plants growing in the understory of the tree help aswell.
I would adjust the watering to the needs of the tree, not that of the top dressing. So if you have maples, beeches, wisteria, etc., water them a lot. The top dressing will stay moist then and moss will eventually start to grow. But if we are talking about Aleppo Pines, Sabina Junipers, Evergreen Oaks, Olives, etc. you’ve got to let them dry out in between watering. I would probably not use any top dressing at all with those species as it doesnt’t make a lot of sense in Spanish climate. That’s what I’ve noticed in the collections I’ve seen in Madrid. It also fits better to the aesthetics of those species, as Olives with fluffy green moss under it seem a little odd whereas the bare soil fits better to their natural appearance.
Hope that helps.
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There is no easy answer to that because there are so many variables. Type of plant, type of soil, depth of pot, just to name a few. The one thing I will say is that the surface dressing or soil on the top of the pot is NOT a reliable indication of the rest of the pot, as it can dry out quickly in sun/wind while the rest of the pot might be totally saturated.
My suggestion would be to start out by inserting something like a chopstick into the soil to and see how much moisture there is in the lower/bottom level. Then use that combined with knowledge about the needs of the particular species (some need to dry out between waterings, some need to stay moist, and some plants transport water faster/slower than others) to decide if it should be watered. Pay close attention (take notes?) and eventually you will get a feel for what your trees need in various conditions and it becomes easier.
I live in Central Washington State (US) where we get close to 300 days of sun a year, it is very dry, and can be quite hot (>100F/38C) for several days in a row. Some of my plants LOVE this, while others (e.g. Dawn Redwood) if I don’t move them into shade during the summer would need to be watered ~4-5 times a day (and probably still not survive). [The sun can be so intense I had to put a shade covering over my 300 gal/1100L Koi pond!]
For the majority of my trees I water once a day (overhead sprinklers) and during the peak of summer I add a short afternoon watering into the schedule, mostly to cool the pots and increase the humidity. For really hot days I may go out and spot water some plants and/or just cool the pots or wet the ground around them to further increase humidity.
I hope this is helpful.
Thank you. I live in Madrid and I know perfectly David Benavente garden as I’m a member of his club. I agree with you in Madrid you cannot use top dressing as reference for watering. But, I wanted to confirm my thought.
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Thank you. You weather conditions are very similar to Madrid. Here the summer is very hot and dry. We can have days with 104F 40C and below 10% of humidity. I always have dificulties in my watering being the pines the more difficult ones. I have killed 2 of then for over watering. Now I learn and try to watering less even ai see the top dry.
I am in Eastern Washington and not quite as hot and dry as a couple of the posters, but close. I have a spray bottle that holds about 2 liters that I use to wet down the top dressing once or twice a day as I work in the garden. I am hoping that along with how I am doing my top dressing will allow me to get it established on more trees this year and keep it over the summer. I also use shade cloth for many trees.
I use a white shelf liner for kitchen cabinets, it is vinyl / rubber and perforated. There are two different types of perforations and I use the spacious one - large holes. A bonsai sales lady in Illinois recommended it for heat reflection. Bird, rodent prevention is an added benefit. I lift my pots to determine water needs. Weight and knowing the trees dry / wet Horticulture